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The combined effects of escape and magnetic field history at Mars
Abstract
Mars is thought to have hosted large amounts of water and carbon dioxide at primitive epochs. The morphological analysis of the surface of Mars shows that large bodies of water were probably present in the North hemisphere at late Noachian (3.7–4 Gyr ago). Was this water solid or liquid? For maintaining liquid water at this time, when the Sun was (likely) less bright than now, a CO2 atmosphere of typically 2 bars is required. Can sputtering, still presently acting at the top of the Martian atmosphere, have removed such a dense atmosphere over the last 3.5–4 Gyr? What was the fate of the 100–200 m global equivalent layer of water present at late Noachian? When did Martian magnetic dynamo vanish, initiating a long period of intense escape by sputtering? Because sputtering efficiency is highly non-linear with solar EUV flux, with a logarithmic slope of ≈7:Φsput≈ΦEUV7, resulting in enhanced levels of escape at primitive epochs, when the sun was several times more luminous than now in the EUV, there is a large uncertainty on the cumulated amount of volatiles removed to space. This amount depends primarily on two factors: (i) the exact value of the non-linearity exponent (≈7 from existing models, but this value is rather uncertain), (ii) the exact time when the dynamo collapsed, activating sputtering at epochs when intense EUV flux and solar wind activity prevailed in the solar system. Both parameters are only crudely known at the present time, due the lack of direct observation of sputtering from Martian orbit, and to the incomplete and insufficiently spatially resolved map of the crustal magnetic field. Precise timing of the past Martian dynamo can be investigated through the demagnetisation signature associated with impact craters. A designated mission to Mars would help in answering this crucial question: was water liquid at the surface of Mars at late Noachian? Such a mission would consist of a low periapsis (≈100 km) orbiter, equipped with a boom-mounted magnetometer, for mapping the magnetic field, as well as adequate in situ mass and energy spectrometers, for a full characterization of escape and of its response to solar activity variations. Surface based observations of atmospheric noble gas isotopic ratios, which keep the signatures of past escape processes, including sputtering for the lightest of them (Ne, Ar), would bring a key constraint for escape models extrapolated back to the past.
... Non-thermal escape can basically be divided into several different types (e.g., Shizgal and Arkos 1996;Chassefière and Leblanc 2004;Chassefière et al. 2007;Kulikov et al. 2007;Lammer et al. 2013;Catling and Kasting 2017), i.e. ...
... The numbers of , however, were later also corrected by to be lower, i.e. ∼ 6 × 10 24 s −1 for present-day, ∼ 3 × 10 25 s −1 for 3 EUV , and ∼ 8 × 10 25 s −1 for 6 EUV . The evolution of all relevant non-thermal escape processes from the present-day to ∼ 3.5 Gyr ago was studied by Chassefière and Leblanc (2004), and Chassefière et al. (2007). Similar to Luhmann et al. (1992) and , these studies also found a significant increase in ion pick-up escape for rising EUV fluxes. ...
... In these studies loss rates of O are generally higher than of C; ionospheric outflow seems further to be less important. A similar behaviour was found by Gillmann et al. (2011) who -based on the work of Chassefière et al. (2007) -also estimated non-thermal escape of C and O during the last ∼ 4 Gyr. It has to be noted, however, that Leblanc (2011a, 2011b) and Chassefière et al. (2013b) re-evaluated their earlier models and found significantly lower rates for sputtering at ∼ 3.5 Gyr ago of only > 10 25 s −1 compared to > 10 27 s −1 in their earlier studies (Chassefière and Leblanc 2004;Chassefière et al. 2007). ...
It is not yet entirely clear whether Mars began as a warm and wet planet that evolved towards the present-day cold and dry body or if it always was cold and dry with just some sporadic episodes of liquid water on its surface. An important clue into this question can be gained by studying the earliest evolution of the Martian atmosphere and whether it was dense and stable to maintain a warm and wet climate or tenuous and susceptible to strong atmospheric escape. We discuss relevant aspects for the evolution and stability of a potential early Martian atmosphere. This contains the solar EUV flux evolution, the formation timescale and volatile inventory of the planet including volcanic degassing, impact delivery and removal, the loss of a catastrophically outgassed steam atmosphere, atmosphere-surface interactions, and thermal and non-thermal escape processes affecting any secondary atmosphere. While early non-thermal escape at Mars before 4 billion years ago (Ga) is poorly understood, particularly in view of its ancient intrinsic magnetic field, research on thermal escape processes indicate that volatile delivery and volcanic degassing cannot counterbalance the strong thermal escape. Therefore, a catastrophically outgassed steam atmosphere of several bars of CO2 and H2O, or CO and H2 for reduced conditions, could have been lost within just a few million years (Myr). Thereafter, Mars likely could not build up a dense secondary atmosphere during its first ~400 Myr but might only have possessed an atmosphere sporadically during events of strong volcanic degassing, potentially also including SO2. This indicates that before ~4.1 Ga Mars indeed might have been cold and dry. A denser CO2- or CO-dominated atmosphere, however, might have built up afterwards but must have been lost later-on due to non-thermal escape processes and sequestration into the ground.
... Non-thermal escape can basically be divided into several different types (e.g., Shizgal and Arkos 1996;Chassefière and Leblanc 2004;Chassefière et al. 2007;Kulikov et al. 2007;Lammer et al. 2013;Catling and Kasting 2017), i.e. ...
... The numbers of , however, were later also corrected by to be lower, i.e. ∼ 6 × 10 24 s −1 for present-day, ∼ 3 × 10 25 s −1 for 3 EUV , and ∼ 8 × 10 25 s −1 for 6 EUV . The evolution of all relevant non-thermal escape processes from the present-day to ∼ 3.5 Gyr ago was studied by Chassefière and Leblanc (2004), and Chassefière et al. (2007). Similar to Luhmann et al. (1992) and , these studies also found a significant increase in ion pick-up escape for rising EUV fluxes. ...
... In these studies loss rates of O are generally higher than of C; ionospheric outflow seems further to be less important. A similar behaviour was found by Gillmann et al. (2011) who -based on the work of Chassefière et al. (2007) -also estimated non-thermal escape of C and O during the last ∼ 4 Gyr. It has to be noted, however, that Leblanc (2011a, 2011b) and Chassefière et al. (2013b) re-evaluated their earlier models and found significantly lower rates for sputtering at ∼ 3.5 Gyr ago of only > 10 25 s −1 compared to > 10 27 s −1 in their earlier studies (Chassefière and Leblanc 2004;Chassefière et al. 2007). ...
It is not yet entirely clear whether Mars began as a warm and wet planet that evolved towards the present-day cold and dry body or if it always was cold and dry with just some sporadic episodes of liquid water on its surface. An important clue into this question can be gained by studying the earliest evolution of the Martian atmosphere and whether it was dense and stable to maintain a warm and wet climate or tenuous and susceptible to strong atmospheric escape. In this review we therefore discuss relevant aspects for the evolution and stability of a potential early Martian atmosphere. This contains the EUV flux evolution of the young Sun, the formation timescale and volatile inventory of the planet including volcanic degassing, impact delivery and removal, the loss of the catastrophically outgassed steam atmosphere, atmosphere-surface interactions, as well as thermal and non-thermal escape processes affecting a potential secondary atmosphere at early Mars. While early non-thermal atmospheric escape at Mars before 4 billion years ago is poorly understood, in particular in view of its ancient intrinsic magnetic field, research on thermal escape processes and the stability of a CO2-dominated atmosphere around Mars against high EUV fluxes indicate that volatile delivery and volcanic degassing cannot counterbalance the strong atmospheric escape. Therefore, a catastrophically outgassed steam atmosphere of several bars of CO2 and H2O, or CO and H2 for reduced conditions, through solidification of the Martian magma ocean could have been lost within just a few million years. Thereafter, Mars likely could not build up a dense secondary atmosphere during its first ∼400 million years but might only have possessed an atmosphere sporadically during events of strong volcanic degassing, potentially also including SO2. This indicates that before ∼4.1 billion years ago Mars indeed might have been cold and dry with at maximum short and sporadic warmer periods. A denser CO2- or CO-dominated atmosphere, however, might have built up afterwards but must have been lost later-on due to non-thermal escape processes and sequestration into the ground.
... 4.1 Solar wind induced ion erosion of the martian CO 2 atmosphere Barabash et al. (2007) used Mars Express ASPERA-3 ion escape data for the investigation of the solar wind erosion of the martian CO 2 atmosphere related to the planet's history. This is also the time period where the martian magnetic dynamo stopped to work so that atmospheric escape of ionized particles could also work (e.g., Chassefière et al., 2007). Barabash et al. (2007) estimated the total CO + 2 solar wind erosion rates and found that Mars loses only a tiny amount at present in the order of ∼8 × 10 22 s −1 . ...
... By estimating this loss rate backward to the end of the Noachian one obtains a total loss equivalent to the surface pressure of about ∼0.2-4 mbar (Barabash 22 H. Lammer et al. et al., 2007). Such low values for the molecular ion loss are within the minimum and maximum values of theoretical studies which yield model depended amounts in the order of ∼0.8-100 mbar (e.g., Ma et al., 2004;Modolo et al., 2005;Chassefière et al., 2007;Lammer et al., 2008;Manning et al., 2010). ...
... One can see that, similar to the case of ion erosion, not much of the main CO 2 atmosphere escaped via this nonthermal loss process since the end of the Noachian. We agree with Chassefière et al. (2007) that it is important to know when the martian magnetic dynamo vanished. Because the sputtering efficiency is highly nonlinear with the solar XUV flux, a long period of intense escape by sputtering could have been initiated in case the martian magnetic dynamo stopped working before 4 Gyr ago. ...
... Brain and Jakosky, 1998;Haberle et al., 1994;Lammer et al., 2013;Manning et al., 2009). These mechanisms include, solar wind escape (also called nonthermal escape) (Chassefiére and Leblanc, 2011;Chassefiére et al., 2007;Lundin et al., 2007), erosion due to solar radiation (thermal escape) (Erkaev et al., 2013;Lundin et al., 2007;Tian et al., 2009), impacts (Ahrens, 1993;Cameron, 1983), volcanic outgassing Morschhauser et al., 2011) and storage of CO 2 into carbonates reservoirs (Haberle et al., 1994). No large carbonate reservoirs have been detected on Mars yet (Bibring et al., 2005;Chevrier et al., 2007), however, traces of carbonates on the surface (Bandfield et al., 2003;Morris et al., 2010), or in Martian meteorites (Bridges et al., 2001) suggest that sequestration of CO 2 into carbonate reservoirs could have taken place throughout the Noachian, Hesperian, and Amazonian periods Niles et al., 2010). ...
... In the baseline model presented in Section 3, impacts constitute a source of volatile rather than an escape mechanism and can deliver up to 2-3 bar of volatiles over the last 4.1 Gyr. Over the same period volcanism can deliver between 50 mbar and 0.5 bar of CO 2 Lammer et al., 2013;Morschhauser et al., 2011) whereas nonthermal escape mechanisms can remove maximum of 200 mbar (Chassefiére et al., 2007;Lammer et al., 2013) and minimum less than 10 mbar (Chassefiére and Leblanc, 2011;Lammer et al., 2013). Consequently, combination of impact erosion and non-thermal escape mechanisms cannot compensate the amount of volatiles delivered by impacts and volcanic outgassing. ...
... However, we computed this scenario with large nonthermal escape (about 200 mbar) while the most recent results only give a maximal of several millibar from these loss mechanisms. Following Chassefiére and Leblanc (2011) a loss of 200 mbar due to non-thermal escape, as estimated by Chassefiére et al. (2007), is too high since it does not take into account the creation of an induced magnetic field by solar wind which decreases the atmospheric loss to less than 10 mbar. If non-thermal escape is less efficient than estimated by Chassefiére et al. (2007), one has to decrease impactor volatile contents and maximal impactor mass even further to more unlikely values so that the final surface pressure could match the present Martian pressure. ...
Early in its history, Mars probably had a denser atmosphere and higher surface temperatures to sustain the presence of stable liquid water or saline solution at the surface. Impacts by asteroids and comets could affect the atmospheric evolution of a planet, by removing part of its atmosphere and by delivering into it material and volatiles. In this study we investigate the atmospheric loss and delivery of volatiles between the end of the Noachian and present, with the help of a semi-analytic model. Our results suggest that impacts alone can hardly remove a significant amount of atmospheric mass over this period. Contribution of additional factors such as outgassing and non-thermal escape processes can not explain neither the presence of surface pressure larger than few hundreds of mbars 3.9 Gyr ago, unless parameter values outside of their expected range are considered. Based on extreme case scenarios, maximum surface pressures at the end of the Noachian, could be as much as 0.25 bar or 1.9 bar, with and without CO2 storage into carbonate reservoirs, respectively.
... This episode of acid deterioration would also explain the absence of carbonates in great quantities on the surface of Mars (they were not detected to date by OMEGA, in spite of its capacity to detect them, even in small proportions), if they were ever formed. It is probable that Mars during Noachian had a dense atmosphere of CO 2 and liquid water circulated on its surface (Chassefière et al., 2007). The respective roles of the trapping in subsurface of water and CO 2 (in the form of carbonates) and the atmospheric exhaust (under the action of solar wind), to explain their disappearance, are not yet wellknown. ...
... The respective roles of the trapping in subsurface of water and CO 2 (in the form of carbonates) and the atmospheric exhaust (under the action of solar wind), to explain their disappearance, are not yet wellknown. Let us note that this question is itself related to the history of the internal activity of Mars and to the stop of its dynamo, the magnetic field that induces limitation of the erosion of atmosphere (Chassefière et al., 2007). ...
Being a first notice in Tunisia, this work opens the door for forthcoming studies shedding light on potential analogies between Tunisian terrestrial analogues and extraterrestrial bodies.
In the first chapter, we investigate models of formation and activity of spring mounds occurring in the Mechertate-Chrita-Sidi El Hani (MCSH) and Boujmal systems. These terrestrial analogues are the mirror of subsurface past terrestrial analogues dating back to the Trias and Messinian. We then use these models to further understand possible spring mounds formation on Mars. In the MCSH system, the genesis of the spring mounds is a direct consequence of groundwater upwelling, triggered by tectonics and/or hydraulics. Considered as fault spring mounds, they are organized along preferential orientations, probably inherited from current or past tectonic activity. This observation supports a tectonic influence in the formation of the spring mounds. On the
one hand, the hydraulic pressure generated by the convergence of aquifers towards the surface of the system allows their consideration as artesian spring mounds. In the case of the MCSH system, our geologic investigations presented here show that both models are worth to be analyzed, and we propose a hydro-tectonic combined model as the adequate formation mechanism of artesian-fault spring mounds. During their evolution
from the embryonic to the islet stages, spring mounds behaving as obstacles are also shaped by an accumulation of a wet aeolian sedimentation, which is enhanced by the induration process. On the other hand, the tectonic model is more candidate to control the formation of spring mounds at the terrestrial analogue of Boujmal. The wet aeolian sedimentology also advocates the accumulation of tephras layers allowing the application of tephrostratigraphy. Similarly, spring mounds may be relatively common in certain provinces on the martian surface, but their mode of formation is still a matter of debate. We propose here that the tectonic, hydraulic, and hydro-tectonic models describing the spring mounds at MCSH should be considered as relevant martian
analogues because: (i) the martian subsurface may be over pressured and this overpressure would originate spring mounds on the surface, (ii) the subsurface may be fractured in such a way that explains the lining up of the spring mounds along preferential orientations, (iii) and the wet aeolian sedimentation through the induration process is a common feature on Mars.
In the second chapter, a multidisciplinary study of the watershed and depressions of the MCSH sabkha system shows that groundwater upwelling and/or seepage toward the modern surface is important in the shaping of its geomorphologic features and sediment outcrops. Along the watershed of the system, groundwater enriched sediment with evaporitic minerals. These minerals precipitate as cement to protect the outcropping sediment from aeolian erosion. The water table is the limiting control on erosion and deposition, and also influences the succession of sediment along the system. It determines the local base level, which controls the deposition within depressions. With increasing humidity at the limit of capillary fringe, the landscape of the evaporative system is organized according three sedimentary types: (1) unconsolidated sediment of aqueous or aeolian origin that is eroded and transported toward depressions (out of reach from groundwater involvement); (2) consolidated sediment is also aqueous or aeolian in origin and is consolidated due groundwater influence (protected from
aeolian erosion); and (3) sedimentary filling of depressions is located within accumulation zones. These sediments are organized along a lateral, basinward profile. Our study shows that during periods of relative water table fall, sediment from the watershed progrades to cover the sabkha basin fill. Applying key concepts of wet aeolian sequence stratigraphy, the rise and fall of the water table and the connected base level results in the deposition of genetically related progradational and retrogradational sequences. These genetic sabkha sequences are useful to interpret the sequence stratigraphy at three locations on Mars, which was controlled by direct groundwater influence. At Meridiani Planum, the deposition of Burns formation starts with a deposition of dry aeolian sediment derived from a former watershed. Then, due to the rise of the water table, wet sediment of a
sabkha rests atop the dry aeolian cycle to comprise a retrogradational sequence. At Terby and Gale craters, an opposite stratigraphic sequence starts with the wet deposition of the sabkha fill. Then, due to the fall of the water table, the dry aeolian sedimentation progrades atop to the sabkha fill to comprise a progradational sequence. We conclude that the various stratigraphic sequences at the MCSH system, described here, represent different possible analogue scenarios for diverse depositional sequences on Mars, in all cases involving groundwater activity.
In the third chapter, we discussed the chaology within the Sidi El Hani terrestrial analogue and Gale crater on Mars. Within natural systems, biologic activities and geologic conditions are linked by hierarchical
cause-effect relations gener g the organic matter within the discharge playa of Sidi El Hani, high percentages of different fractions seem abnormal in such a saline context. As it has been interpreted in previous works about Sahelarea, this maturated organic matter may be due to a human polluting activity. But this hypothesis seems less
convincing because this region is outside any polluting activity. Thus, this maturated organic matter should be
viewed in a widest context of a multidisciplinary study taking into account of the presence of petroleum
potentials in the subsurface, the converging hydrogeology and the tectonized region. For instance, the high
percentage of Aromatic Polycyclic Hydrocarbon (APH) may be hence the result of a hydrocarbons migration
rather than anthropogenic pollution. The hydrocarbon migration towards the surface of Sidi El Hani discharge
playa may be argued based on the model of fluid migration towards Mars surface. That is to say, based on what happens on Mars, we explain the case on terrestrial analogues.
Key Words: Terrestrial analogue, Mechertate-Chrita-Sidi El Hani and Boujmal systems, groundwater upwelling, spring mounds, wet aeolian sedimentation, tephrostratigraphy, wet aeolian sequence stratigraphy, Meridiani Planum, Terby crater, Gale crater, chaology, cyclostratigraphy, hydrocarbon migration, fluid migration on Mars.
... A planet's mass impacts planetary habitability in multiple ways. It provides radiogenic heating from long-lived radionuclides to drive internal heating and tectonics (Lenardic and Crowley 2012), as well as generation of a magnetic field (Driscoll and Barnes 2015), which is a key parameter that determines atmospheric retention (Chassefière et al. 2007;Lammer 2012;Egan et al. 2019). Planetary mass, via planetary gravity, also controls atmospheric scale height, which can change the rate the planet radiates to space, and modify its climate and the limits of the HZ . ...
... Magnetic fields are an important factor when considering the habitability of a planet, as they may protect planets from losing volatiles (such as water) through stellar wind interactions (Chassefière et al. 2007;Lundin et al. 2007;Lammer 2012;Driscoll and Bercovici 2013;do Nascimento et al. 2016;Driscoll 2018). However, this "magnetic umbrella" hypothesis is still debated, as the magnetic field may also increase the interaction area with the solar wind, which could drive increased escape (Brain et al. 2013;Egan et al. 2019). ...
Habitability is a measure of an environment's potential to support life, and a habitable exoplanet supports liquid water on its surface. However, a planet's success in maintaining liquid water on its surface is the end result of a complex set of interactions between planetary, stellar, planetary system and even Galactic characteristics and processes, operating over the planet's lifetime. In this chapter, we describe how we can now determine which exoplanets are most likely to be terrestrial, and the research needed to help define the habitable zone under different assumptions and planetary conditions. We then move beyond the habitable zone concept to explore a new framework that looks at far more characteristics and processes, and provide a comprehensive survey of their impacts on a planet's ability to acquire and maintain habitability over time. We are now entering an exciting era of terrestiral exoplanet atmospheric characterization, where initial observations to characterize planetary composition and constrain atmospheres is already underway, with more powerful observing capabilities planned for the near and far future. Understanding the processes that affect the habitability of a planet will guide us in discovering habitable, and potentially inhabited, planets.
... A planet's mass impacts planetary habitability in multiple ways. It provides radiogenic heating from long-lived radionuclides to drive internal heating and tectonics (Lenardic and Crowley 2012), as well as generation of a magnetic field (Driscoll and Barnes 2015), which is a key parameter that determines atmospheric retention (Chassefière et al. 2007;Lammer 2012;Egan et al. 2019). Planetary mass, via planetary gravity, also controls atmospheric scale height, which can change the rate the planet radiates to space, and modify its climate and the limits of the HZ . ...
... Magnetic fields are an important factor when considering the habitability of a planet, as they may protect planets from losing volatiles (such as water) through stellar wind interactions (Chassefière et al. 2007;Lundin et al. 2007;Lammer 2012;Driscoll and Bercovici 2013;do Nascimento et al. 2016;Driscoll 2018). However, this "magnetic umbrella" hypothesis is still debated, as the magnetic field may also increase the interaction area with the solar wind, which could drive increased escape (Brain et al. 2013;Egan et al. 2019). ...
We use a one-dimensional (1-D) cloud-free climate model to estimate habitable zone (HZ) boundaries for terrestrial planets of masses 0.1 M and 5 M around circumbinary stars of various spectral type combinations. Specifically, we consider binary systems with host spectral types F-F, F-G, F-K, F-M, G-G, G-K, G-M, K-K, K-M and M-M. Scaling the background N2 atmospheric pressure with the radius of the planet, we find that the inner edge of the HZ moves inwards towards the star for 5ME compared to 0.1ME planets for all spectral types. This is because the water-vapor column depth is smaller for larger planets and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. The outer edge of the HZ changes little due to competing effects of the albedo and greenhouse effect. While these results are broadly consistent with the trend of single star HZ results for different mass planets, there are significant differences between single star and binary star systems for the inner edge of the HZ. Interesting combinations of stellar pairs from our 1-D model results can be used to explore for in-depth climate studies with 3-D climate models. We identify a common HZ stellar flux domain for all circumbinary spectral types
... We list the atmospheric ion and photochemical escape rates in Table 1 and plot them in Figure 4; see also Figure 4 of Luhmann et al. (1992) and Chassefière et al. (2007) where similar calculations were undertaken based on less comprehensive methods. The calculated atmospheric escape rates in Table 1 are consistent with the density contour plots illustrated in Figures 2 and 3. ...
... The calculations do not include other potentially important loss processes such as sputtering; therefore, it provides a lower limit on the escape rates. Our result is more conservative compared to earlier studies (Zhang et al. 1993;Luhmann 1997;Chassefière et al. 2007;Valeille et al. 2010) that predicted ( ) 10 m of water was depleted over Martian history. ...
In this Letter, we make use of sophisticated 3D numerical simulations to assess the extent of atmospheric ion and photochemical losses from Mars over time. We demonstrate that the atmospheric ion escape rates were significantly higher (by more than two orders of magnitude) in the past at ∼4 Ga compared to the present-day value owing to the stronger solar wind and higher ultraviolet fluxes from the young Sun. We found that the photochemical loss of atomic hot oxygen dominates over the total ion loss at the current epoch, while the atmospheric ion loss is likely much more important at ancient times. We briefly discuss the ensuing implications of high atmospheric ion escape rates in the context of ancient Mars, and exoplanets with similar atmospheric compositions around young solar-type stars and M-dwarfs.
... We list the atmospheric ion and photochemical escape rates in Table 1 and plot them in Figure 4; see also Fig. 4 of Luhmann et al. (1992) and Chassefière et al. (2007) where similar calculations were undertaken based on less comprehensive methods. The calculated atmospheric escape rates in Table 1 are consistent with the density con- Table 1. ...
... The calculations do not include other potentially important loss processes such as sputtering; therefore, it provides a lower limit on the escape rates. Our result is more conservative compared to earlier studies (Zhang et al. 1993;Luhmann 1997;Chassefière et al. 2007;Valeille et al. 2010) that predicted O(10) m of water was depleted over Martian history. Before proceeding further, recall that our analytic estimates were expressible asṄ ∝ t −α andṄ O ∝ t −β with α ≈ 2.33 and β ≈ 1.19. ...
In this Letter, we make use of sophisticated 3D numerical simulations to assess the extent of atmospheric ion and photochemical losses from Mars over time. We demonstrate that the atmospheric ion escape rates were significantly higher (by more than two orders of magnitude) in the past at Ga compared to the present-day value owing to the stronger solar wind and higher ultraviolet fluxes from the young Sun. We found that the photochemical loss of atomic hot oxygen dominates over the total ion loss at the current epoch whilst the atmospheric ion loss is likely much more important at ancient times. We briefly discuss the ensuing implications of high atmospheric ion escape rates in the context of ancient Mars, and exoplanets with similar atmospheric compositions around young solar-type stars and M-dwarfs.
... (Weiss et al. 2002). More recent estimates based on crater counts overlap with the age range 4.1 ± 0.2 Ga (Chassefière et al. 2007) further supporting this conclusion. ...
... Rather, later interpretations invoke nonspecific mechanisms involving crustal recycling to explain the polarity variation (Whaler and Purucker 2005), yet they still assume age differences for differently magnetized areas of the crust. Cratering records seem to bear this out (Chassefière et al. 2007), as they do for the weak-to-absent crustal magnetization of the Northern hemispheric dichotomy and the Argyre and Hellas impact basins Whaler and Purucker 2005). Fig. 1 Feasibility of running a dynamo in a liquid silicate mantle in Mars as a function of mid-mantle heat flux Q m . ...
Crustal magnetization of rocks in regions of Mars surface testifies to an era of dynamo activity. I examine the possibility that the dynamo that operated then, in the first 400–600 Ma after Mars formed, was powered by a crystallizing subsurface magma ocean. Of the ways that a magma ocean dynamo could operate, on Mars only turbulent and magnetostrophic dynamos seem feasible; geostrophic dynamos do not seem so unless very high heat flows, 100–1000 times present, are invoked. Given the anticipated information from the future InSight lander mission, it will be difficult to assess where the dynamo originated unless an inner core is discovered, rendering the dynamo likely to have operated in the core.
... Une des conséquences d'un échappement intense d'hydrogène est l'entraînement des espèces plus lourdes présentes dans la haute atmosphère, l'oxygène et le carbone atomiques (Hunten 1973). Ce mécanisme, connu sous le nom d'échappement hydrodynamique, pourrait expliquer l'état actuel de l'atmosphère de Mars, son appauvrissement en volatile, ainsi que l'absence d'eau sur Vénus (Hunten 1993 ;Chassefière et al. 2007 ;Gilmann et al. 2009). Il ne peut cependant pas expliquer les rapports isotopiques du D/H dans l'atmosphère martienne car ne fractionne pas efficacement des espèces aussi légères (Hunten 1993). ...
... l'ionisation de l'exosphère par le rayonnement solaire suivi de l'accélération de ces nouveaux ions par le vent solaire (« pick-up ion », figure 4), l'échappement ionosphérique et des mécanismes photochimiques (section 2.1.1). Les modèles les plus récents montrent que ces mécanismes pourraient expliquer une perte massive d'éléments lourds comme l'oxygène et le carbone, entre il y a 4.1 milliards d'années (la fin de la dynamo) et aujourd'hui Chassefière et al. 2007). Mon premier travail sur les mécanismes d'échappement a donné lieu au développement du premier modèle 3D de l'interaction entre l'atmosphère martienne et les ions accélérés par le vent solaire et susceptibles de reimpacter l'atmosphère martienne (Luhmann et al. 1991 ;1992 ;Leblanc and Johnson 2001). ...
The exosphere of a planetary object is the transtion region between the environment dominated by this object (its atmosphere or its surface) and the environment dominated by any other object, that can be a planet or a star. My research, during these last ten years, was dedicated to model and to observe various exospheres of our solar system, in particular, Mars and Mercury exospheres. During this defense, I will illustrate what do we mean by exosphere, what can be learned from the exosphere on the evolution of a planetary object and what needs to be done in order to progress in this field, either theoretically or instrumentally.
... Exploring the physical processes that affect the volatiles in Martian atmosphere will help provide a better understanding of the water and CO 2 inventories on Mars [e.g., Carr, 1986;Pepin, 1994;Jakosky and Jones, 1997;McElroy, 1972]. Throughout the Martian history, the loss mechanisms and the escape rates of Martian atmosphere have changed [Chassefiére et al., 2007;Luhmann, 1992;Melosh and Vickery, 1989]. Observations from spacecraft and analyses of Martian geomorphology suggest that the early Martian atmosphere was much warmer, wetter, and abundant in water and CO 2 , which was substantially different from the current atmospheric condition [e.g., Chassefiére et al., 2007;Jakosky, 1991]. ...
... Throughout the Martian history, the loss mechanisms and the escape rates of Martian atmosphere have changed [Chassefiére et al., 2007;Luhmann, 1992;Melosh and Vickery, 1989]. Observations from spacecraft and analyses of Martian geomorphology suggest that the early Martian atmosphere was much warmer, wetter, and abundant in water and CO 2 , which was substantially different from the current atmospheric condition [e.g., Chassefiére et al., 2007;Jakosky, 1991]. The deficiency of water and CO 2 in the current atmosphere raises questions as to the processes that led to the loss of volatiles and their subsequent fate. ...
Two important source reactions for hot atomic carbon on Mars are photodissociation of CO and dissociative recombination of CO+; both reactions are highly sensitive to solar activity and occur mostly deep in the dayside thermosphere. The production of energetic particles results in the formation of hot coronae that are made up of neutral atoms including hot carbon. Some of these atoms are on ballistic trajectories and return to the thermosphere and others escape. Understanding the physics in this region requires modeling that captures the complicated dynamics of hot atoms in 3D. This study evaluates the carbon atom inventory by investigating the production and distribution of energetic carbon atoms using the full 3D atmospheric input. The methodology and details of the hot atomic carbon model calculation are given, and the calculated total global escape of hot carbon from the assumed dominant photochemical processes at a fixed condition, equinox (Ls = 180°) and low solar activity (F10.7 = 70 at Earth), are presented. To investigate the dynamics of these energetic neutral atoms, we have coupled a self-consistent a 3D global kinetic model, the Adaptive Mesh Particle Simulator (AMPS), with a 3D thermosphere / ionosphere model, the Mars Thermosphere General Circulation Model (MTGCM) to provide a self-consistent global description of the hot carbon corona in the upper thermosphere and exosphere. The spatial distributions of density and temperature and atmospheric loss are simulated for the case considered.
... Many of these processes are understood from our own solar system. From studies of Mars, Chassefière et al. (2007) and Lundin et al. (2007) defined four primary nonthermal processes. ...
High-energy X-ray and ultraviolet (UV) radiation from young stars impacts planetary atmospheric chemistry and mass loss. The active ∼22 Myr M dwarf AU Mic hosts two exoplanets orbiting interior to its debris disk. Therefore, this system provides a unique opportunity to quantify the effects of stellar X-ray and UV irradiation on planetary atmospheres as a function of both age and orbital separation. In this paper, we present over 5 hr of far-UV (FUV) observations of AU Mic taken with the Cosmic Origins Spectrograph (COS; 1070-1360 Å) on the Hubble Space Telescope (HST). We provide an itemization of 120 emission features in the HST/COS FUV spectrum and quantify the flux contributions from formation temperatures ranging from 10 ⁴ to 10 ⁷ K. We detect 13 flares in the FUV white-light curve with energies ranging from 10 ²⁹ to 10 ³¹ erg s. The majority of the energy in each of these flares is released from the transition region between the chromosphere and the corona. There is a 100× increase in flux at continuum wavelengths λ < 1100 Å in each flare, which may be caused by thermal Bremsstrahlung emission. We calculate that the baseline atmospheric mass-loss rate for AU Mic b is ∼10 ⁸ g s ⁻¹ , although this rate can be as high as ∼10 ¹⁴ g s ⁻¹ during flares with L flare ≃ 10 33 erg s ⁻¹ . Finally, we model the transmission spectra for AU Mic b and c with a new panchromatic spectrum of AU Mic and motivate future JWST observations of these planets.
... Dynamo timing has been suggested to affect climate evolution on early Mars , linking interior and surface/atmospheric processes. The change in ancient climate conditions from a thick atmosphere that allowed liquid water to persist (at least temporarily or intermittently) on the martian surface to a much thinner atmosphere (e.g., Chassefière et al., 2007;Wordsworth et al., 2015), could suggest a causal relation between atmospheric escape and a global dynamo field. However, this notion has been questioned (Brain et al., 2013(Brain et al., , 2016. ...
Mars’ crustal magnetic field holds information on the planet’s interior evolution and exterior processes that have modified the crust. Crustal magnetization records an ancient dynamo field that indicates very different interior conditions in the past, possibly linked to the presence of a thicker early atmosphere. Current data sets have provided a wealth of information on the ancient magnetic field, and on the acquisition and modification of magnetization in the crust. However, many puzzles remain regarding the nature and origin of crustal magnetization, and the timing and characteristics of the past dynamo. Here we use recent advances in understanding martian magnetism to highlight open questions, and ways in which they can be addressed through laboratory analysis, modeling and new data sets. Many of the outstanding key issues require data sets that close the gap in spatial resolution between available global satellite and local surface magnetic field measurements. Future missions such as a helicopter, balloon or airplane can provide areal high resolution coverage of the magnetic field, vital to major advances in understanding planetary crustal magnetic fields.
... The detection of hydrated minerals on the surface of Mars may also constitute evidence that water was present in the liquid state during the Noachian period (Section I.2.3.2) During the Hesperian period, liquid water flows become rarer due to the escape of atmospheric molecules under the action of the sun, associated with the precipitation of CO2 into carbonates and the trapping of water in the subsurface, by serpentinization, or in the form of water ice (Chassefière, et al. 2007;Lammer, et al. 2013). However, catastrophic flow morphologies from this period are observed in the northern hemisphere and attest to the presence of liquid water during the Hesperian. ...
The question of if terrestrial life is alone in the universe is a philosophical and scientific question that has captivated humanity since ancient times. This thesis approaches its science and technical questions from the idea that life is composed of, and generates, organic matter. This thesis focuses on the search for organic matter on the surface of Mars by gas chromatography-mass spectrometry (GC-MS) onboard the Viking Lander, the future ExoMars Mars Organic Molecule Analyser (MOMA) experiment, and with applications to the Sample Analysis at Mars (SAM) experiment onboard the Mars Science Laboratory (MSL). In this thesis, the Viking GC-MS data sets have been reexamined and evidence is presented for the presence of chlorobenzene, a potential reaction product of martian carbon and martian chlorine during pyrolysis. The performance of the ExoMars MOMA integrated chromatographic system is assessed by experiments carried out with a laboratory setup that reproduces the flight configuration and mimics in situ operating conditions. Results demonstrate the ability of the GC subsystem to identify a wide range of organic and inorganic volatile compounds, including biomolecular signatures, within the constrained operating conditions of MOMA. Next, the MOMA GC-MS pyrolysis and wet chemistry protocol is explored with a more complex set of samples in which organic compounds are adsorbed to amontmorillonite mineral matrix across concentrations and with or without the addition of magnesium perchlorate. This study shows that the MOMA GC-MS package enables detection of each target organic molecule or its products in the presence of the clay mineral. Finally, perspectives are presented on the specific complexities to more complex natural samples (e.g., suites of species, trace organics) and to space experimentation (e.g., complex gas processing systems, adsorption/desorption trapping) that can present unique challenges for Mars surface experiments in the strict identification of target compounds such as amino acids. The results presented in this thesis reevaluate the interpretation of past Mars GC-MS mission data and will collectively aid in the implementation of Mars surface operations and the interpretation of potential data obtained by ExoMars’s MOMA experiment. In addition, this thesis offers results and discussion that can be applied to the interpretation of the SAM GC-MS analysis currently operating on Mars.
... A rough chronology has been established by crater counting, and was corroborated by in situ radiometric dating performed by Curiosity (Farley et al., 2014). The early shutdown of Mars's core magnetic dynamo exposed the atmosphere to sputtering by solar radiation and allowed charged particles to escape along solar magnetic field lines (Chassefière et al., 2007). The bulk of the atmosphere was thus lost over time, causing surface pressure, temperature, and habitability to decline ~4-3 Ga ago (Jakosky et al., 2017). ...
Astrobiology seeks to understand the origin, evolution, distribution, and future of life in the universe and thus to integrate biology with planetary science, astronomy, cosmology, and the other physical sciences. The discipline emerged in the late 20th century, partly in response to the development of space exploration programs in the United States, Russia, and elsewhere. Many astrobiologists are now involved in the search for life on Mars, Europa, Enceladus, and beyond. However, research in astrobiology does not presume the existence of extraterrestrial life, for which there is no compelling evidence; indeed, it includes the study of life on Earth in its astronomical and cosmic context. Moreover, the absence of observed life from all other planetary bodies requires a scientific explanation, and suggests several hypotheses amenable to further observational, theoretical, and experimental investigation under the aegis of astrobiology. Despite the apparent uniqueness of Earth’s biosphere— the “n = 1 problem”—astrobiology is increasingly driven by large quantities of data. Such data have been provided by the robotic exploration of the Solar System, the first observations of extrasolar planets, laboratory experiments into prebiotic chemistry, spectroscopic measurements of organic molecules in extraterrestrial environments, analytical advances in the biogeochemistry and paleobiology of very ancient rocks, surveys of Earth’s microbial diversity and ecology, and experiments to delimit the capacity of organisms to survive and thrive in extreme conditions.
... Phillips et al. (2001) suggest that the growth of Tharsis may have contributed up to 1.5 bar of CO 2 ; however, depending on Martian mantle redox state, outgassed CO 2 may not have been sufficient to make a significant difference to atmospheric pressure (Stanley et al., 2011). The possible major sinks for the atmosphere are escape to space (Chassefière et al., 2007;Dong et al., 2018;Jakosky et al., 2018), impact erosion of the atmosphere (Pham & Karatekin, 2016;Schlichting et al., 2015), carbonate formation (Stephens & Stevenson, 1990;Wray et al., 2016), surface weathering (Baker, 2017), transport of CO 2 into the subsurface (Kurahashi- Nakamura & Tajika, 2006;Manning et al., 2019), and condensation into ice caps (Bierson et al., 2016). Ion escape, sputtering, and photochemical loss mechanisms such as dissociative recombination are all strongly dependent on solar EUV flux and solar wind mass flux (e.g., Ayres, 1997;Brain et al., 2016;Chassefière & Leblanc, 2004) which have both decreased over geologic time (e.g., Dorren & Guinan, 1994;Tu et al., 2015). ...
Mars' climate history depends in part on its atmospheric pressure evolution, but most existing constraints on atmospheric pressure are indirect. Thin atmospheres allow small objects to reach the surface and form impact craters; therefore, ancient impact craters can constrain past atmospheric pressure. To identify ancient craters preserved in sedimentary rocks and exhumed by wind erosion, we use HiRISE orthoimages, anaglyphs, and digital terrain models (DTMs). We compare measured crater populations from two sites to predictions from an atmosphere‐impactor interaction model for atmospheres of different pressures. Our upper limits on continuous atmospheric pressure are 1.9±0.1 bar around 4 Ga and 1.5±0.1 bar at 3.8±0.2 Ga. We demonstrate that atmospheric pressure cannot have been continuously above these upper limits. During the interval 3.8±0.2 Ga, our crater counts require that atmospheric pressure was less than 5% of Earth's modern pressure for at least 10⁴ yrs, or at higher pressure for a correspondingly longer duration of time (at least 10⁵−10⁶ years at 1.5 bar for our Mawrth phyllosilicates and Meridiani Planum data, respectively). Therefore, atmospheric pressure around 4 Ga was either continuously 1.9±0.1 bar or varied between higher (>1.9 bar) and lower (<1.9 bar) pressures. Similarly, atmospheric pressure at 3.8±0.2 Ga was either continuously 1.5±0.1 bar, or varied between higher (>1.5 bar) and lower (<1.5 bar) pressures. Finally, we synthesize all available paleopressure estimates for early Mars to constrain a 2‐component model of Mars' long‐term atmospheric pressure evolution. In our model, atmospheric pressures <1 bar early in Mars' history best fit existing paleopressure constraints.
... Our results suggest -in agreement with previous studies -that the main loss of atomic carbon at present Mars is due to photodissociation of CO. According to the present simulations, the total carbon loss is about 0.8 and 3.2 × 10 24 s −1 for low and high solar activity (Table 13) , respectively, which is ∼ 5 − 15 times higher compared to the estimated average atmospheric sputtering of C atoms (Chassefière et al., 2007) and up to ∼ 40 times higher compared to the estimated CO + 2 molecular ion escape from ASPERA-3 (Barabash et al., 2007). The present results are in accord with the suggestion of Lammer et al. (2013) that the escape of photochemically produced suprathermal C atoms, which originate from the dissociation of CO + 2 , CO + and CO are the most efficient processes for the loss of the martian CO 2 atmosphere at present. ...
The escape of hot O and C atoms from the present martian atmosphere during low and high solar activity conditions has been studied with a Monte-Carlo model. The model includes the initial energy distribution of hot atoms, elastic, inelastic, and quenching collisions between the suprathermal atoms and the ambient cooler neutral atmosphere, and applies energy dependent total and differential cross sections for the determination of the collision probability and the scattering angles. The results yield a total loss rate of hot oxygen of during low and high solar activity conditions and is mainly due to dissociative recombination of O and CO. The total loss rates of carbon are found to be 0.8 and for low and high solar activity, respectively, with photodissociation of CO being the main source. Depending on solar activity, the obtained carbon loss rates are up to times higher than the CO ion loss rate inferred from Mars Express ASPERA-3 observations. Finally, collisional effects above the exobase reduce the escape rates by about with respect to a collionless exophere.
... Most nonthermal escape processes are associated with the presence of ions and their behavior in the electric and magnetic field. Photochemical escape is a nonthermal escape process important for Mars (e.g., McElroy 1972;Ip 1988;Nagy and Cravens 1988;Lammer and Bauer 1991;Fox and Hać 2009;Krestyanikova and Shematovich 2006;Chassefière et al. 2007;Chaufray et al. 2007;Gröller et al. 2014) but is unlikely to be an efficient escape mechanism on Venus Gröller et al. 2010), Earth or super Earths because the maximum kinetic energy an oxygen atom can obtain from dissociative recombination reaction of O + 2 is fixed and lower than the escape energies of planets more massive than Mars. Neutral atoms and molecules in the atmosphere of the planet may be ionized through photoionization, impact ionization, or charge exchange with solar wind ions. ...
... Fig. 4 shows an early Mars with the hypothesized northern ocean residing at its highest level beginning in the Early Noachian; a period of evolving surface conditions, including heightened impact rates, volatile redistribution, surface precipitation and standing bodies of water. Figs. 5 and 6 depict the subsequent evolution of this environment through the end of the Noachian, when climate begins to change to conditions resembling those of today, most likely resulting from the extinction of the planet's magnetic dynamo, progressive freezing, sublimation, and cold-trapping of water in an evolving cryosphere and at higher latitudes (Clifford et al., 2010), as well as loss to space of volatiles through impact and solar wind erosion (Jakosky, 1990;Chassefiere et al., 2006;Stanley et al., 2008;Tian et al., 2009). The result of these combined processes was a global decline in ocean levels at the end of the Noachian and into the Hesperian, when environmental conditions suitable to maintain surface water ceased to exist. ...
The evolution of Mars as a water-bearing body is of considerable interest for the understanding of its early history and evolution. The principles of terrestrial sequence stratigraphy provide a useful conceptual framework to hypothesize about the stratigraphic history of the planets northern plains. We present a model based on the hypothesized presence of an early ocean and the accumulation of lowland sediments eroded from highland terrain during the time of the valley networks and later outflow channels. Ancient, global environmental changes, induced by a progressively cooling climate would have led to a protracted loss of surface and near surface water from low-latitudes and eventual cold-trapping at higher latitudes -- resulting in a unique and prolonged, perpetual forced regression within basins and lowland depositional environments. The Messinian Salinity Crisis (MSC) serves as a potential terrestrial analogue of the depositional and environmental consequences relating to the progressive removal of large standing bodies of water. We suggest that the evolution of similar conditions on Mars would have led to the emplacement of diagnostic sequences of deposits and regional scale unconformities, consistent with intermittent resurfacing of the northern plains and the progressive loss of an early ocean by the end of the Hesperian era.
... Our model is capable of connecting the atmospheric escape modeling with geochemical records (isotopic data). The atmospheric escape rates from early Mars remain uncertain; the estimates on the sputtering rate vary in the previous studies (e.g., Luhmann et al. 1992;Chassefière et al. 2007;Chassefière and Leblanc 2011). The ongoing MAVEN mission (Jakosky et al. 2015) will provide better understanding of escape mechanisms and estimates on the escape rates from early Mars by observing the response of the Martian atmosphere to solar activity. ...
We examine the history of the loss and replenishment of the Martian atmosphere using elemental and isotopic compositions of nitrogen and noble gases. The evolution of the atmosphere is calculated by taking into consideration various processes: impact erosion and replenishment by asteroids and comets, atmospheric escape induced by solar radiation and wind, volcanic degassing, and gas deposition by interplanetary dust particles. Our model reproduces the elemental and isotopic compositions of N and noble gases (except for Xe) in the Martian atmosphere, as inferred from exploration missions and analyses of Martian meteorites. Other processes such as ionization-induced fractionation, which are not included in our model, are likely to make a large contribution in producing the current Xe isotope composition. Since intense impacts during the heavy bombardment period greatly affect the atmospheric mass, the atmospheric pressure evolves stochastically. Whereas a dense atmosphere preserves primitive isotopic compositions, a thin atmosphere on early Mars is severely influenced by stochastic impact events and following escape-induced fractionation. The onset of fractionation following the decrease in atmospheric pressure is explained by shorter timescales of isotopic fractionation under a lower atmospheric pressure. The comparison of our numerical results with the less fractionated N (N/N) and Ar (Ar/Ar) isotope compositions of the ancient atmosphere recorded in the Martian meteorite Allan Hills 84001 provides a lower limit of the atmospheric pressure in 4 Ga to preserve the primitive isotopic compositions. We conclude that the atmospheric pressure was higher than approximately 0.5 bar at 4 Ga.
... Most nonthermal escape processes are associated with the presence of ions and their behavior in the electric and magnetic field. Photochemical escape is a nonthermal escape process important for Mars (e.g., McElroy 1972;Ip 1988;Nagy and Cravens 1988;Lammer and Bauer 1991;Fox and Hać 2009;Krestyanikova and Shematovich 2006;Chassefière et al. 2007;Chaufray et al. 2007;Gröller et al. 2014) but is unlikely to be an efficient escape mechanism on Venus Gröller et al. 2010), Earth or super Earths because the maximum kinetic energy an oxygen atom can obtain from dissociative recombination reaction of O + 2 is fixed and lower than the escape energies of planets more massive than Mars. Neutral atoms and molecules in the atmosphere of the planet may be ionized through photoionization, impact ionization, or charge exchange with solar wind ions. ...
The origin and evolution of planetary protoatmospheres in relation to the protoplanetary disk is discussed. The initial atmospheres of planets can mainly be related via two formation scenarios. If a protoplanetary core accretes mass and grows inside the gas disk, it can capture H2, He and other gases from the disk. When the gas of the disk evaporates, the core that is surrounded by the H2/He gas envelope is exposed to the high X-ray and extreme ultraviolet flux and stellar wind of the young host star. This period can be considered as the onset of atmospheric escape. It is shown that lower mass bodies accrete less gas and depending on the host stars radiation environment can therefore lose the gaseous envelope after tens or hundreds of million years. Massive cores may never get rid of their captured hydrogen envelopes and remain as sub-Neptunes, Neptunes or gas giants for their whole life time. Terrestrial planets which may have lost the captured gas envelope by thermal atmospheric escape, or which accreted after the protoplanetary nebula vanished will produce catastrophically outgassed steam atmospheres during the magma ocean solidification process. These steam atmospheres consist mainly of water and CO2 that was incorporated into the protoplanet during its accretion. Planets, which are formed in the habitable zone, solidify within several million years. In such cases the outgassed steam atmospheres cool fast, which leads to the condensation of water and the formation of liquid oceans. On the other hand, magma oceans are sustained for longer if planets form inside a critical distance, even if they outgassed a larger initial amount of water. In such cases the steam atmosphere could remain 100 million years or for even longer. Hydrodynamic atmospheric escape will then desiccate these planets during the slow solidification process.
... On the other hand, ion outflow in the form of polar wind and auroral processes are likely to be stronger due to the concentrating effects of the polar cusp region (Chassefière and Leblanc 2004). The combined result of these effects have not been thoroughly studied for Mars; though it is generally assumed that loss rates were higher without a dynamo present (Chassefière et al. 2007), other work suggests that a weak dipolar field (∼ 10 nT at the surface) may cause maximal atmospheric loss (Kallio and Barabash 2012;). In any case, it is clear that the history of the Mars dynamo is inextricably linked to the history of atmospheric loss. ...
Two of the primary goals of the MAVEN mission are to determine how the rate of escape of Martian atmospheric gas to space at the current epoch depends upon solar influences and planetary parameters and to estimate the total mass of atmosphere lost to space over the history of the planet. Along with MAVEN’s suite of nine science instruments, a collection of complementary models of the neutral and plasma environments of Mars’ upper atmosphere and near-space environment are an indispensable part of the MAVEN toolkit, for three primary reasons. First, escaping neutrals will not be directly measured by MAVEN and so neutral escape rates must be derived, via models, from in situ measurements of plasma temperatures and neutral and plasma densities and by remote measurements of the extended exosphere. Second, although escaping ions will be directly measured, all MAVEN measurements are limited in spatial coverage, so global models are needed for intelligent interpolation over spherical surfaces to calculate global escape rates. Third, MAVEN measurements will lead to multidimensional parameterizations of global escape rates for a range of solar and planetary parameters, but further global models informed by MAVEN data will be required to extend these parameterizations to the more extreme conditions that likely prevailed in the early solar system, which is essential for determining total integrated atmospheric loss. We describe these modeling tools and the strategies for using them in concert with MAVEN measurements to greater constrain the history of atmospheric loss on Mars.
... Cependant, le CO 2 a probablement été libéré graduellement par le volcanisme tout au long de l'histoire de Mars, si bien que des conditions avec une atmosphère plus dense qu'aujourd'hui aurait pu persister sur des temps courts, notamment lorsque le flux UV du jeune Soleil a commencé à décroître (il ne valait plus que 10 fois sa valeur actuelle il y a 3.7 Ga). L'importance précise de l'échappement de l'atmosphère primitive de Mars reste encore mal connue, et dépend notamment de l'état magnétique de la planète dans sa jeunesse (Chassefière et al., 2007). La nouvelle mission MAVEN de la NASA, arrivée en septembre 2014 en orbite autour de Mars, devrait apporter plus de contraintes sur les processus d'érosion spatiale des atmosphères planétaires. ...
This thesis work is devoted to the physical characterization of the Martian surface and to the study of dynamic processes modifying it. Two aspects are addressed. The first concerns the thermo-physical properties which are a mean to putting constraints on to the erosive and sedimentary actions summed over the geologic history. The second is the hydration of the Martian surface which plays, as a planetary reservoir of water, an important role on the Martian climate.In order to characterize these two physical parameters of the Martian surface, we have combined the orbital view which allows a global coverage with in situ measurements, which provides a robust local interpretation, and we have used tools allowing numerical simulations of physical processes. Data from OMEGA, an imaging spectrometer onboard Mars Express orbiting Mars since 2004, and from the ground temperature sensor of the REMS instrument onboard Curiosity have been analyzed in details. Surface temperature measurements from these two instruments have been inverted using a climate model for characterizing the thermo-physical properties of the Martian surface. We present the first global map of the Martian surface thermal inertia constructed from OMEGA data and we directly highlight for the first time some thermal behavior caused by heterogeneous mixtures or neglected physical processes at the surface of Mars.Information regarding the hydration of the Martian surface have been extracted from OMEGA data using a large set of laboratory experiments. This information has been interpreted together with scientific results from multiple mission orbiting or at the surface of Mars and with numerical simulations of the Martian water cycle in order to reconstruct the history of this hydration. We find that the hydration remains stable throughout the whole Martian year and that it increases with latitude with an asymetry between the two hemispheres. The spatial distribution of the hydration fits areas that are in regular contact with water frost, which therefore seems to be involved in the process of water implementation in the Martian regolith.
... In the same way as for surface interacting with the solar wind, this interaction can lead to the ejection of matter above the atmosphere, populating the exosphere (). In the case of Mars, this interaction could have led to a significant erosion of Mars' atmosphere during the early solar system (Chassefière et al. 2007) (see Sect. 6.2.2). ...
Space weather has become a mature discipline for the Earth space environment. With increasing efforts in space exploration, it is becoming more and more necessary to understand the space environments of bodies other than Earth. This is the background for an emerging aspect of the space weather discipline: planetary space weather. In this article, we explore what characterizes planetary space weather, using some examples throughout the solar system. We consider energy sources and timescales, the characteristics of solar system objects and interaction processes. We discuss several developments of space weather interactions including the effects on planetary radiation belts, atmospheric escape, habitability and effects on space systems. We discuss future considerations and conclude that planetary space weather will be of increasing importance for future planetary missions.
... The study of Martian exosphere is important for understanding the escape of Mars' atmosphere, which is linked to the loss of thick atmosphere Mars had in the past and its impact on Mars' climate change [16]. [14]. ...
Despite several missions including flyby, orbiters, and landers, the Martian upper atmosphere-exosphere, region above 400 km from surface, still remains unexplored in-situ in terms of its neutral density distribution and composition. The first vertical profiling of the atmospheric composition of Mars was conducted by the Viking 1 and 2 Landers [1-3], where the altitudinal profiles of the atmospheric composition and density were studied from 200 to 120 km range. In addition to the Viking missions, there have been attempts to derive the atmospheric densities by radio tracking methods (Mars Odyssey [4]; MARSIS of Mars Express, Mars Reconnaissance Orbiter) and spacecraft drag (Mars Global Surveyor [5]) measurements as well as detection of few species through remote sensing of their spectroscopic emissions in Mariner 6, 7, 9 missions [6-8], and SPICAM and PFS in Mars Express [9, 10, 11]. Recent remote sensing observations made by ALICE-FUV imaging spectrometer aboard ROSETTA mission during February 2007 [12] suggest an extended Martian H corona up to several tens of 1000 km from the surface. However, there is no in-situ observation on the atmospheric composition and density in the exosphere of Mars, i.e., beyond 400 km from Martian surface. In order to fill this gap in our understanding, we propose to fly a quadrupole mass spectrometry-based Neutral Mass Spectrometer, working in the 1-300 amu mass range, called " MENCA " (Mars Exospheric Neutral Composition Analyser) in a Mars orbiter. MENCA will explore the Martian exospheric neutral density and composition from ~500 km and beyond. The visualization of the MENCA instrument is shown in Figure 1.
... For example, Venus and Mars are believed to have lost the majority of their atmospheres. Evidence of the presence of large amounts of water flowing on Mars (e.g., Chassefière et al. 2007) contrasts with the small amounts of water that are observed on it now. Similarly, if Venus had the same amount of volatiles as Earth in its atmosphere after its creation and if no significant atmospheric erosion had occurred, its atmosphere would contain much more O 2 and H 2 O than what is currently observed. ...
Characterizing Earth- and Venus-like exoplanets' atmospheres to determine if they are habitable and how they are evolving (e.g., equilibrium or strong erosion) is a challenge. For that endeavor, a key element is the retrieval of the exospheric temperature, which is a marker of some of the processes occurring in the lower layers and controls a large part of the atmospheric escape. We describe a method to determine the exospheric temperature of an O2- and/or CO2-rich transiting exoplanet, and we simulate the respective spectra of such a planet in hydrostatic equilibrium and hydrodynamic escape. The observation of hydrodynamically escaping atmospheres in young planets may help constrain and improve our understanding of the evolution of the solar system's terrestrial planets' atmospheres. We use the dependency of the absorption spectra of the O2 and CO2 molecules on the temperature to estimate the temperature independently of the total absorption of the planet. Combining two observables (two parts of the UV spectra that have a different temperature dependency) with the model, we are able to determine the thermospheric density profile and temperature. If the slope of the density profile is inconsistent with the temperature, then we infer the hydrodynamic escape. We address the question of the possible biases in the application of the method to future observations, and we show that the flare activity should be cautiously monitored to avoid large biases.
... According to the present simulations, by dividing through the martian hemispheric surface at 400 km altitude. Density [cm -3 ] 0 Altitude [km] total CO + h ν CO + e Table 13), respectively, which is $ 5–15 times higher compared to the estimated average atmospheric sputtering of C atoms (Chassefière et al., 2007) and up to $ 40 times higher compared to the estimated CO 2 þ molecular ion escape from ASPERA-3 (Barabash et al., 2007). The present results are in accord with the suggestion of Lammer et al. (2013) that the escape of photochemically produced suprathermal C atoms, which originate from the dissociation of CO 2 þ , CO þ and CO are the most efficient processes for the loss of the martian CO 2 atmosphere at present. ...
The escape of hot O and C atoms from the present martian atmosphere
during low and high solar activity conditions has been studied with a
Monte-Carlo model. The model includes the initial energy distribution of
hot atoms, elastic, inelastic, and quenching collisions between the
suprathermal atoms and the ambient cooler neutral atmosphere, and
applies energy dependent total and differential cross sections for the
determination of the collision probability and the scattering angles.
The results indicate that dissociative recombination of O^+_2 and CO^+_2
are the major sources for the loss of hot oxygen giving loss rates of
about 3×10^25 s^-1 during low and high solar activity
conditions, whereas the loss of atomic carbon is mainly due to
photodissociation of CO with escape rates of about 1 × 10^24
s^-1 and 3 × 10^24 s^-1 for low and high solar
activity, respectively. Depending on solar activity, the obtained carbon
loss rates are up to ∼ 35 times higher than the CO^+2 ion loss rate
inferred from Mars Express ASPERA-3 observations.
... When the dynamo-driven global magnetic field disappeared, the early Mars atmosphere was thereafter exposed directly to the solar wind, which was likely substantially stronger than in recent times [Wood et al., 2005]. Thus, the rate of atmospheric erosion likely increased significantly [Chassefiere et al., 2007] from that time onward. It is therefore important to determine whether this occurred in the early Hesperian (model age of~3.7-3.8 ...
[1] Large impacts simultaneously reset both the surface age and the magnetization of the entire depth of crust over areas comparable to the final size of the resulting craters. These properties make large impact craters (>300 km in diameter) ideal “magnetic markers” for constraining the history of the Martian core dynamo. However, the relationship between crustal magnetization and magnetic field measured in orbit is nonunique, making the measured magnetic field signature of an impact crater only a proxy for the magnetization (or lack thereof) below. Using Monte Carlo Fourier domain modeling of subsurface magnetization, we calculate probability distributions of the magnetic field signatures of partially and completely demagnetized craters. We compare these distributions to measured magnetic field signatures of 41 old impact craters on Mars larger than 300 km in diameter and calculate probabilities of their magnetization state. We compare these probabilities to cratering densities and absolute model ages and in this manner arrive at a robust time history of Martian large-crater magnetization and hence of the Martian dynamo. We conclude that the most likely scenario was a Mars dynamo active when the oldest detectable basins formed, ceasing before the Hellas and Utopia impacts, between 4.0 and 4.1 Ga (in model age) and not thereafter restarting. The Mars atmosphere was thereafter exposed directly to erosion by the solar wind, significantly altering the path of climate evolution. Further improvements to the history of the Martian dynamo will require better crater age estimates and lower altitude magnetic field data.
... According to the present simulations, Table 14 Escape fluxes of hot atomic carbon obtained in previous studies. Altitude [km] total CO + h ν CO + e Table 13), respectively, which is $ 5-15 times higher compared to the estimated average atmospheric sputtering of C atoms ( Chassefière et al., 2007) and up to $ 40 times higher compared to the estimated CO 2 þ molecular ion escape from ASPERA-3 ( Barabash et al., 2007). The present results are in accord with the suggestion of Lammer et al. (2013) that the escape of photochemically produced suprathermal C atoms, which originate from the dissociation of CO 2 þ , CO þ and CO are the most efficient processes for the loss of the martian CO 2 atmosphere at present. ...
... This initial pressure varies between 5050 Pa with a constant temperature and 5400 Pa with a changing temperature. How does this compare to Mars? Keeping in mind that Daisy's atmosphere is much simpler than Mars'one, the computed pressure and the estimated values of the martian ground pressure after the late heavy bombardment at Mars (Chassefière et al., 2007) are of the same order of magnitude: the ground pressure 3.5 Gy ago must have been about 6000 Pa. After this period, several mechanisms which are not taken into account in this study took place such as the sputtering, volcanism, solar wind effects, etc. ...
In the recent years, the presence of dications in the atmospheres of
Mars, Venus, Earth and Titan has been modeled and assessed. These
studies also suggested that these ions could participate to the escape
of the planetary atmospheres because a large fraction of them is
unstable and highly ener- getic. When they dissociate, their internal
energy is transformed into kinetic energy which may be larger than the
escape energy. This study assesses the impact of the doubly-charged ions
in the escape of CO2-dominated planetary atmospheres and to compare it
to the escape of thermal photo-ions.We solve a Boltzmann transport
equation at daytime taking into account the dissociative states of CO++
for a simplified single constituent atmosphere of a 2 case-study planet.
We compute the escape of fast ions using a Beer-Lambert approach. We
study three test-cases. On a Mars-analog planet in today's conditions,
we retrieve the measured electron escape flux. When comparing the two
mechanisms (i.e. excluding solar wind effects, sputtering ...), the
escape due to the fast ions issuing from the dissociation of dications
may account for up to 6% of the total and the escape of thermal ions for
the remaining. We show that these two mechanisms cannot explain the
escape of the atmosphere since the magnetic field vanished but
complement the other processes and allow writing the scenario of the
Mars escape. We show that the atmosphere of a Mars analog planet would
empty in another giga years and a half. At Venus orbit, the contribution
of the dications in the escape rate is negligible.When simulating the
hot Jupiter HD209458b, the two processes cannot explain the measured
escape flux of C+.
... [41] The climatic history of Mars based on geomorphological evidence provides clues to the cessation of the dynamo since an internally generated magnetic field can help prevent atmospheric constituents from escape, as discussed by Chassefière et al. [2007]. Sandu and Kiefer [2012] included the effects of magmatic degassing in thermal evolution models and presented plausible initial conditions that end dynamo activity 500-800 million years after the formation of Mars. ...
The lack of magnetic anomalies within the major impact basins (Hellas,
Argyre, and Isidis) has led many investigators to the conclusion that
Mars' dynamo shut down prior to the time when these basins formed
(∼4.0 Ga). We test this hypothesis by analyzing gravity and magnetic
anomalies in the regions surrounding Tyrrhenus Mons and Syrtis Major,
two volcanoes that were active during the late Noachian and Hesperian.
We model magnetic anomalies that are associated with gravity anomalies
and generally find that sources located below Noachian surface units
tend to favor paleopoles near the equator and sources located below
Hesperian surface features favor paleopoles near the geographical poles,
suggesting polar wander during the Noachian-Hesperian. Both paleopole
clusters have positive and negative polarities, indicating reversals of
the field during the Noachian and Hesperian. Magnetization of sources
below Hesperian surfaces is evidence that the dynamo persisted beyond
the formation of the major impact basins. The demagnetization associated
with the volcanic construct of Syrtis Major implies dynamo cessation
occurred while it was geologically active approximately 3.6 billion
years ago. Timing of dynamo activity is fundamentally linked to Mars'
climate via the stability of its atmosphere, and is coupled to the
extent and duration of surface geologic activity. Thus, the dynamo
history is key for understanding both when Mars was most geologically
active and when it may have been most hospitable to life.
This chapter studies the thermodynamic parameters of the external geodynamics of Mars. As matter of fact, the thermodynamics on Mars surface are basically controlled by the solar forcing and the internal geodynamics of the planet. In relation to the physical and chemical characteristics of water on Mars, we can build the Martian chronology. First, the Phyllosian is the phyllosilicates thermodynamics era. Second, the Theiikian is the age of sulfate thermodynamics. Third, the Siderikian, according to siderikos (ferric in Greek), is the era of anhydrous ferric oxides thermodynamics. The Martian chronology may be also built on catering. So, the meteoritic bombardment is linked to increasing disorder in the solar systems. That is to say, it is quite linked to the thermodynamics of the solar system. As direct repercussions of variable thermodynamics during the Mars history, the authors investigate the sedimentology and stratigraphy in different localities on Mars: Arabia Terra, Meridiani Planum, Terby Crater, and Gale Crater.
We provide a comprehensive update of photochemical escape rates of atomic carbon from the present-day Martian atmosphere using a one-dimensional photochemical model and a Monte Carlo escape model. The photochemical model incorporates new results relevant to carbon photochemistry at Mars, including new cross sections for photodissociation of CO2 into C and O2 (Lu et al. 2014) and electron impact dissociation of CO (Ajello et al. 2019). We find the newly included channel of CO2 photodissociation to be the largest contributor to C escape, at 34%–58%. CO photodissociation and CO+ dissociative recombination, which have been discussed extensively in the literature, also show up as significant sources of hot C atoms, with respective contributions of 15%–23% and 7%–10%. Electron impact dissociation of CO2 (11%–15%) and photoionization of CO (6%–20%) are also important channels. Overall, escape rates vary over 3–11×1023 s⁻¹, with an increase of 70% at perihelion compared to aphelion, and a much larger increase of 133% at solar maximum compared to solar minimum. While these present escape rates give a total integrated escape of only 1.3 mbar of CO2 when multiplied by 3.6 billion years, the better characterization of carbon photochemistry and escape from this study will enable us to more reliably extrapolate backwards in time to when conditions of the Martian atmosphere were significantly different from those of today.
While devoid of an active magnetic dynamo field today, Mars possesses a remanent magnetic field that may reach several thousand nanoteslas locally. The exact origin and the events that have shaped the crustal magnetization remain largely enigmatic. Three magnetic field data sets from two spacecraft collected over 13 cumulative years have sampled the Martian magnetic field over a range of altitudes from 90 up to 6,000 km: (a) Mars Global Surveyor (MGS) magnetometer (1997–2006), (b) MGS Electron Reflectometer (1999–2006), and (c) Mars Atmosphere and Volatile EvolutioN (MAVEN) magnetometer (2014 to today). In this paper we combine these complementary data sets for the first time to build a new model of the Martian internal magnetic field. This new model improves upon previous ones in several aspects: comprehensive data coverage, refined data selection scheme, modified modeling scheme, discrete‐to‐continuous transformation of the model, and increased model resolution. The new model has a spatial resolution of ∼160 km at the surface, corresponding to spherical harmonic degree 134. It shows small scales and well‐defined features, which can now be associated with geological signatures.
It is believed that Mars underwent drastic climate change, changing its environment from warm and wet to cold and dry. This gives rise to the idea that Mars may have hosted life in the past and, indeed, may do so even today. Atmospheric evolution is thus an important key to understanding the history of Martian habitability. However, precise estimates of past atmospheric inventories including water, and their loss mechanisms, are difficult to be obtained. Recent studies have highlighted various interesting facts related to (i) the efficiency of mass transport from the lower to upper atmospheric reservoir and (ii) the deep energetic particle precipitation into the atmosphere from space. These new insights tell us that Mars is a mutually coupled system comprising the planet’s surface, lower and upper atmospheres, and the surrounding space environment. These relationships potentially imply an upward revision of the estimate of total atmospheric loss to space. Another relevant issue relates to the indirect signs of life in the Martian atmosphere. Scientists are particularly intrigued by clear evidence of a biological/geological signature, such as methane (CH4) in the Martian atmosphere. Although the presence of CH4 is still under debate because of large measurement uncertainties, the forthcoming ESA-Roscosmos mission, which employs the Trace Gas Orbiter (TGO), will settle questions on the existence of this gas and its origin.
Habitability is a measure of an environment’s potential to support life, and for exoplanets this is tied to the presence of surface liquid water. Whether or not an exoplanet is able to maintain liquid water on its surface is due to a complex interplay of planetary, stellar, and planetary system characteristics over the planet’s lifetime. Although a planet’s habitability depends critically on the effect of stellar type and planetary semimajor axis on climate balance, many additional factors can also impact habitability. Processes which can modify a habitable planet’s environment include photochemistry; stellar effects on climate balance; atmospheric loss; gravitational interactions with the star, moons, other planets and minor bodies; and galactic phenomena. Here we briefly review characteristics and processes that can impact exoplanet habitability. Ultimately, understanding these processes will enable identification of those exoplanets that are most likely to be habitable and will illuminate global characteristics of habitable planets that may be observable.
We address the problem of the dissipation (escape) of planetary atmospheres and discuss the physical mechanisms controlling the nature of the relevant processes and review the mathematical models and numerical methods used in the analy-sis of this phenomenon, taking the limitations imposed by available experimental data into account. The structural and dynamic features of the aeronomy of Earth and terrestrial planets are discussed in detail; they are key in determining the energy absorption rate and the atmosphere escape rate. A kinetic Monte Carlo method developed by the authors for investigating the thermal and nonthermal processes of atmo-spheric escape is presented. Using this approach and spacecraft data, atomic loss rates from the Venusian and Martian atmo-spheres via a variety of escape processes are estimated, and their role at the current and early evolutionary stages of these planets is discussed. The discovery of exosolar planets, model studies of the dissipation of their gas envelopes, and the likely impact of the dissipation mechanisms on the planetary atmosphere and climate evolution have stimulated the study of this field and made it a topical research subject.
The history of Mars’ atmosphere is important for understanding the geological evolution and potential habitability of the planet. We determine the amount of gas lost to space through time using measurements of the upper-atmospheric structure made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. We derive the structure of ³⁸Ar/³⁶Ar between the homopause and exobase altitudes. Fractionation of argon occurs as a result of loss of gas to space by pickup-ion sputtering, which preferentially removes the lighter atom. The measurements require that 66% of the atmospheric argon has been lost to space. Thus, a large fraction of Mars’ atmospheric gas has been lost to space, contributing to the transition in climate from an early, warm, wet environment to today’s cold, dry atmosphere.
Aeronomy is a description of the physics and chemistry of the upper atmospheres and ionospheres of planetary bodies. In this chapter we consider those processes occurring in the upper atmosphere that determine the structure of the corona and lead to molecular escape.
Recent measurements of the present-day Ar abundance and isotopic ratios in the Martian atmosphere by the SAM instrument suite onboard the Curiosity rover can be used to constrain the atmospheric and volatile evolution. We have examined the role of volcanic outgassing, escape to space via sputtering, crustal erosion, impact delivery, and impact erosion in reproducing the Ar isotope ratios from an initial state 4.4 billion years ago. To investigate the effects of each of these processes, their timing, and their intensity we have modeled exchanges of Ar isotopes between various reservoirs (mantle, crust, atmosphere, etc.) throughout Mars’ history. Furthermore, we use present-day atmospheric measurements to determine the parameter space consistent with observations. We find that significant loss to space (at least 48% of atmospheric 36Ar) is required to match the observed 36Ar/38Ar ratio. Our estimates of volcanic outgassing do not supply sufficient 40Ar to the atmosphere to match observations, so in our model at least 31% of 40Ar produced in the crust must have also been released to the atmosphere. Of the total 40Ar introduced into the atmosphere about 25% must have been lost to space. By adding the present-day isotopic abundances with our results of total integrated Ar loss we find a “restored” value of atmospheric 40Ar/36Ar, which represents what that ratio would be if the total integrated Ar loss had remained in the atmosphere. We determine the restored value to be ∼ 900–1500 – below the present Martian atmospheric value (1900 ± 300), but 3–5 times greater than the terrestrial value.
Generation of gravity waves by convection was studied using a nonlinear two-dimensional model. A boundary-layer convection forced by a horizontally-uniform heating and a plume forced by a localized heating representing a local dust storm were tested. The results suggest that vigorous convection occurs due to the low density of the martian atmosphere and that short-period waves having frequencies near the buoyancy frequency can be preferentially generated. The propagation of those gravity waves to thermospheric heights was studied using a linearized one-dimensional model. Because of the fast vertical propagation the waves attain large amplitudes in the lower thermosphere, being consistent with Mars Global Surveyor and Mars Odyssey’s accelerometer measurements and MAVEN’s neutral and ion measurements. The heating and cooling caused by the waves are expected to be significant in the energy budget of the thermosphere, and the vertical mixing induced by those gravity waves should influence the homopause height. Since the thermospheric densities of light, minor species increase with the lowering of the homopause, a lower homopause may have enhanced the escape of such species to space for early Mars, where slower, weaker gravity waves should dominate.
Since 2004, the twin rovers Spirit and Opportunity of the MER (Mars Exploration Rover) mission have been investigating their respective landing sites at Gusev Crater and Meridiani Planum. This PhD thesis deals with the analysis and the interpretation of the data from the APXS (Alpha-Particle X-ray Spectrometer) instrument located on the robotic arm of each rover and whose role is to determine the chemical composition of Martian rocks and soils by X-ray spectrometry. Thanks to their extraordinary longevity, Spirit and Opportunity have been able to reach distances several km from their initial landing sites and the APXS instruments have analyzed numerous samples, yielding clues about the role that water could have played in the Martian past. In a first time, I chose to investigate this diversity of samples thanks to a multidimensional analysis technique. This allowed me to perform a classification of samples and to highlight the petrogenetic relationships between rocks and soils from Gusev and Meridiani. I will present the main results obtained with this method and their connections with the spatial and stratigraphic organisation of the samples. Then I will show how these results led me to explore a numerical geochemical model of SO3 acid fog alteration of Martian basalts. I will describe the hypotheses of this model before comparing its results with MER data. We will finally see what are the implications about the geology of the sites of Gusev and Meridiani, and more generally about the geological history of Mars and the conditions that prevailed at its surface in the past.
The extreme radiation and plasma environments during the period of the young active Sun/Stars have important implications for the evolution of planetary atmospheres and may be responsible that planets with a low gravity like early Mars most likely could never build up a dense atmosphere during the first few 100 Myr after their origin. On the other hand more massive planets such as super-Earths even in orbits within the habitable zone of their host stars might not lose their initial protoatmospheres completely. These planets could end up as water worlds with CO and hydrogen- or O-rich upper atmospheres. If an atmosphere of a terrestrial planet evolves to an N-dominated atmosphere too early in its lifetime, the atmosphere may escape to space. By comparing the escape related atmospheric evolution between Venus, the Earth, and Mars, one finds that the initial conditions set up by the planetary formation processes and the interaction between the early atmospheres with the young Sun’s or host star’s X-ray and EUV flux as well as the plasma environment (e.g., winds, CMEs, etc.) influence strongly the factors to which a planet may evolve to an Earth-like class I habitat.
We present the temporal variability of the atomic and molecular hydrogen density derived from a 3D General Circulation Model describing the Martian atmosphere from the surface to the exobase. A kinetic exospheric model is used to compute the hydrogen density above the exobase. We use these models to study the diurnal and seasonal variations of the hydrogen density and the Jeans escape rate as well as their variations with solar activity, assuming a classic dust scenario. We find that the diurnal variations of the hydrogen density are important with a peak in the dawn region during equinoxes and a peak on the nightside during solstices. These features result from the dynamics of the Martian upper atmosphere. The variations of the atomic hydrogen Jeans escape with seasons and solar activity are in the range 1.3x1025 s-1 – 4.4x1026 s-1. A factor ∼8 is due to the seasonal variations with a maximum during the winter solstice in the northern hemisphere and a minimum during the summer solstice in the northern hemisphere that we attribute to the variation of the Mars-Sun distance. A factor ∼5 is due to the solar cycle with a maximum escape rate at high solar activity. The variations of the molecular hydrogen Jeans escape with seasons and solar activity are in the range 3x1022 s-1 – 6x1024 s-1. A factor ∼10 is due to the seasonal variations with a maximum during the winter solstice in the northern hemisphere and a minimum during the summer solstice in the northern hemisphere. A factor ∼20 is due to the solar cycle with a maximum escape rate at high solar activity. If Jeans escape is the major escape channel for hydrogen, the hydrogen escape is never limited by diffusion. The hydrogen density above 10,000 km presents seasonal and solar cycle variations similar to the Jeans escape rate at all latitudes and local times. This 3D temporal model of the hydrogen thermosphere/exosphere will be useful to interpret future MAVEN observations and the consequences of the hydrogen corona variability on the Martian plasma environment.
The fate of water which was present on early Mars remains enigmatic. We
propose a simple model based on serpentinization, a hydrothermal
alteration process which may produce magnetite and store water. Our
model invokes serpentinization during about 500 to 800 Myr, while a
dynamo is active, which may have continued after the formation of the
crustal dichotomy. We show that the present magnetic field measured by
Mars Global Surveyor in the southern hemisphere is consistent with a
~500 m thick Global Equivalent Layer (GEL) of water trapped in
serpentine. Serpentinization results in the release of H2.
The released H atoms are lost to space through thermal escape,
increasing the D/H ratio in water reservoirs exchanging with atmosphere.
We show that the value of the D/H ratio in the present atmosphere (~5)
is also consistent with the serpentinization of a ~500 m thick water
GEL. We reassess the role of nonthermal escape in removing water from
the planet. By considering an updated solar wind-ionosphere interaction
representation, we show that the contribution of oxygen escape to H
isotopic fractionation is negligible. Our results suggest that
significant amounts of water (up to a ~330-1030 m thick GEL) present at
the surface during the Noachian, similar to the quantity inferred from
the morphological analysis of valley networks, could be stored today in
subsurface serpentine.
Several mechanisms have been invoked in the past to explain the Mars atmospheric escape, ranging from thermal to non-thermal. Most of them rely on the solar energy inputs through solar wind and EUV emission variations. In the present paper, we propose a new mechanism also linked to the solar EUV flux. This additional source of atmospheric escape is from the doubly charged molecular ions. We show that this source can account to 8 to 15% of the total escape and may trigger other mechanisms.
The discovery of high concentrations of water-ice just below the Martian surface polar areas made by Mars Odyssey has strengthened the debate about the search for life on Mars. Generally it is believed that life on Earth emerged in liquid water from the processing of organic molecules. Thus, the possible origin of life on early Mars should have been related to the evolution of the planetary water inventory, consequently it is important to know the amount of water-ice stored below the planetary surface. The search and mapping of the present subsurface water and ice reservoirs will be carried out experimentally by Mars Express with its Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) ground-penetrating radar in the near future. We estimate the present and past water-ice reservoirs, which are and were in exchange with the atmosphere by using the observed D/H ratio in the atmospheric water vapour, measured D/H ratios in Martian SNC meteorites and D/H isotope ratios based on a study by Lunine etal. (2003) regarding asteroid and cometary water delivery to early Mars. Using the results of this study with initial D/H ratios of about 1.215 m. By assuming that hydrodynamic escape fractionated the D/H ratio to a value that is stored in the old Martian SNC meteorites with a measured average enrichment of about 2.3 times the TSW ratio we estimate a present water-ice reservoir equivalent to a global layer with a thickness of about 11–27 m. From the obtained range of the estimated present water-ice deposit, we estimate a water-ice reservoir exchangeable with the atmosphere on Mars 3.5 Ga equivalent to a global ocean with a thickness of between 17 and 61 m. All the estimated reservoirs depend on the escape of water from Mars since 3.5 Ga equivalent to a global ocean with a thickness of about 14 m (minimum) to 34 m (maximum). The main uncertainties in the estimate of the minimal and maximal water-ice reservoir is related to the present uncertainties in the efficiency of atmospheric escape rates triggered by plasma instabilities and momentum transfer effects between the solar wind and the ionosphere. However, these uncertainties will be reduced in the near future, since both loss processes will be studied in detail by the Automatic Space Plasma Experiment with a Rotating Analyzer (ASPERA-3) on-board Mars Express. The obtained results combined with the discovery of the present water-ice subsurface reservoirs by the MARSIS radar and isotope studies as presented in this work, will also give us an idea of how enriched the atmosphere was in D compared with H after the heavy bombardment corresponding to a better understanding of the efficiency of the hydrodynamic escape process due to the young Sun.
The consequences of an early epoch of plate tectonics on Mars followed by single-plate tectonics with stagnant lid mantle convection on both crust production and magnetic field generation have been studied with parameterized mantle convection models. Thermal history models with parameterized mantle convection, not being dynamo models, can provide necessary, but not sufficient, conditions for dynamo action. It is difficult to find early plate tectonics models that can reasonably explain crust formation, as is required by geological and geophysical observations, and allow an early magnetic field that is widely accepted as the cause for the observed magnetic anomalies. Dating of crust provinces and topography and gravity data suggest a crust production rate monotonically declining through the Noachian and Hesperian and a present-day crust thickness of more than 50 km. Plate tectonics cools the mantle and core efficiently, and the core may easily generate an early magnetic field. Given a sufficiently weak mantle rheology, plate tectonics can explain a field even if the core is not initially superheated with respect to the mantle. Because the crust production rate is proportional to temperature, however, an early efficient cooling will frustrate later crust production and therefore cannot explain, for example, the absence of prominent magnetic anomalies in the northern crustal province and the northern volcanic plains in the Early Hesperian. Voluminous crust formation following plate tectonics is possible if plate tectonics heat transfer is inefficient but then the crust growth rate has a late peak (about 2 Ga b.p.), which is not observed. These models also require a substantial initial superheating of the core to allow a dynamo. If one accepts the initial superheating, then, as we will show, a simple thermal evolution model with monotonic cooling of the planet due to stagnant lid mantle convection underneath a single plate throughout the evolution can better reconcile early crust formation and magnetic field generation.
Large (diameter greater than ~500 km) Martian impact basins are associated with observed magnetic fields which are statistically distinct from, and smaller than, fields associated with smaller craters. We suggest that this effect arises because impacts cause shock, heating, and excavation, reducing the magnetization of previously magnetized crust. For a simple, uniformly magnetized model the magnetic field at 100 km altitude is reduced by ~50% when a crater-shaped demagnetization zone reaches the base of the magnetized layer. By analogy with terrestrial data, we assume that in Martian craters the zone of demagnetization extends to a depth of 0.04-0.15 crater diameters. On the basis of this assumption, the data suggest that the depth to the base of the magnetized layer on Mars, if uniform, is ~35 km, with lower and upper bounds of 10 and 100 km, respectively. These bounds imply magnetizations of 5-40 Am-1 and are consistent with likely Mars geotherms at 4 Gyr B.P.
The martian atmospheric D/H value of 5.2 times terrestrial is
significantly higher than any found on Earth, and has been ascribed to
preferential loss of H relative to D from the atmosphere through Jeans
escape over time. Here, based on ion microprobe analyses of apatite
grains from martian meteorite QUE94201, it is shown that the pre-Jeans
escape martian water reservoir has a D/H value ˜twice that of
terrestrial water, rather than the “terrestrial” value that
has been assumed in prior work. The data support a two-stage history for
martian volatiles in which early hydrodynamic escape enriched martian
water to ˜2x terrestrial D/H values. Subsequent Jeans escape to
produce the current atmospheric values has thus been responsible for
less D-enrichment than previously thought. A martian crust containing
2-3 times more water than previously proposed is implied by the
results.
1] We present the results of the first three-dimensional (3-D) simulation of the water isotope HDO in the Martian atmosphere. This deuterated isotope of water has long been used on both Earth and Mars as a proxy to understand the climatic evolutions of these planets. On Mars, the current enrichment in deuterium concentration in the atmosphere is believed to be indirect evidence of a wetter climate in the past. Due to its vapor pressure being lower than that of H 2 O, HDO gets fractionated at condensation and therefore concentrates in the Martian water ice clouds. Our study aims at understanding the latitudinal, vertical, and temporal variations of this species under current Martian climate. Our results indicate that the globally averaged D/H ratio in the Martian atmosphere should vary modestly with season, with changes on the order of 2%. Locally, however, this same ratio exhibits large annual changes (by a factor of 2) in the high-latitude regions. These fluctuations are controlled by the Polar Hood water ice clouds, within which HDO gets heavily fractionated. Due to the combined action of summer clouds above the north polar cap and to the cold-trapping effect of the south residual cap, the global atmospheric deuterium concentration is predicted to be more than 15% lower than the concentration in the north permanent cap ice. We thus extrapolate by suggesting that the ''true'' D/H ratio of Martian water may exceed 6.5 (wrt. SMOW), rather than the 5.6 inferred from atmospheric probing. The globally and annually averaged vertical distribution of HDO exhibits a mild decline with altitude, a result in significant contrast with previous 1-D studies. These results will help constrain more accurately the photochemical models aimed at understanding the observed low concentration of deuterium at high altitudes and thus the process of water escape to space.
There are several reasons to believe that Mars could have become an
Earth like planet rather than the present dry and cold planet. In
particular, many elements suggest the presence of liquid water at the
Martian surface during a relatively short period at an early stage of
its history. Since liquid water may have been the birthplace for life on
Earth, the fate of Martian water is one of the major key and yet
unanswered question to be solved. Mars Escape and Magnetic Orbiter
(MEMO) is a low periapsis orbiter of Mars devoted to the measurement of
present escape and the characterization of the fossil magnetic field of
Mars. The use of a low periapsis altitude orbit (120-150 km) is required
to detect and quantify all populations of atoms and molecules involved
in escape. It is also required to measure the magnetic field of Mars
with an unprecedented spatial resolution that would allow getting a more
precise timing of the dynamo and its disappearance. Achieving a full
characterization of atmospheric escape, and extrapolating it back to the
past requires: (i) to measure escape fluxes of neutral and ion species,
and characterize the dynamics and chemistry of the regions of the
atmosphere where escape occurs (thermosphere, ionosphere, exosphere), as
well as their responses to solar activity, and (ii) to characterize the
lateral variations of the magnetic field of lithospheric origin, and by
extension, the timing of the Martian dynamo. Of particular interest is
the extinction of the dynamo that is thought to have enhanced the
atmospheric escape processes still operating today. The proposed
low-periapsis orbiter will consist of the following elements: • An
"Escape Package" to characterize by both in-situ and remote measurements
the thermosphere, ionosphere, exosphere and solar wind interaction
regions (from one hundred to several thousand km), including thermal,
suprathermal 1 and energetic particles. • A "Magnetic Field
Package", to characterize the magnetization of the lithosphere, and in
particular the contrasts between magnetized and demagnetized areas,
which cannot be accomplished with the present MGS coverage. This package
will also serve for the characterization of escape processes. • A
"Preparing to Aero-assistance Package", to measure atmospheric and
meteorological parameters (density, temperature, wind) in the
aerocapture region (which extends down to about 40 km altitude), to
allow physical 3-D fields of parameters from the middle atmosphere up to
the high thermosphere to be built. A mission like MEMO would ideally
complete the present European program for the exploration of Mars by
contributing to our understanding of what has made the Earth suitable
for life and not Mars. 2
Mars is thought to have possessed a dynamo that ceased similar to0.5 b.y. after the formation of the planet. A possible, but ad hoc, explanation is an early episode of plate tectonics, which drove core convection by rapid cooling of the mantle. We present an alternative explanation: that the Martian core was initially hotter than the mantle after core formation, providing an initial high heat flux out of the core. A core initially 150 K hotter than the mantle can explain the early dynamo without requiring plate tectonics. Recent experimental results suggest that potassium is likely to partition into the Martian core, potentially providing an extra source of energy to power a dynamo. We find that the radioactive decay of K-40 cannot explain the inferred dynamo history without the presence of a hot core. Our results also suggest that core solidification is unlikely to have occurred, because this process would have generated a long-lived (>1 b.y.) dynamo. If, as we conclude, the core is entirely liquid, it must contain at least similar to5 wt% sulfur. An initially hot core is consistent with geochemical evidence for rapid core formation and incomplete thermal equilibration with the mantle. Thus, the early history of planetary dynamos provides constraints on the processes of accretion and differentiation.
9 [1] The equivalent source dipole technique is used to model the three components of 10 the Martian lithospheric magnetic field. We use magnetic field measurements made on 11 board the Mars Global Surveyor spacecraft. Different input dipole meshes are presented 12 and evaluated. Because there is no global, Earth-like, inducing magnetic field, the 13 magnetization directions are solved for together with the magnetization intensity. A first 14 class of models is computed using either low-altitude or high-altitude measurements, 15 giving some statistical information about the depth of the dipoles. Then, a second class of 16 models is derived on the basis of measurements made between 80 and 430 km altitude. 17 The 4840 dipoles are placed 20 km below the surface, with a mean spacing of 2.92° 18 (173 km). Residual rms values between observations and predictions are as low as 15 nT 19 for the total field, with associated correlation coefficient equal to 0.97. The resulting 20 model is used to predict the magnetic field at 200-km constant altitude. We present the 21 maps of the magnetic field and of the magnetization. Downward continuation of a 22 spherical harmonic model derived from our equivalent source solution suggests that 23 intermediate-scale lithospheric fields at the surface probably exceed 5000 nT. Given an 24 assumed 40-km-thick magnetized layer, with a mean volume per dipole equal to 3.6.10 6 25 km 3 , the magnetization components range between ±12 A/m. We also present apparent 26 correlations between some impact craters (!300-km diameter) and magnetization 27 contrasts. Finally, we discuss the implications of the directional information and possible 28 magnetic carriers.
Recent observations of deuterium atoms at Lyman alpha with the Hubble Space Telescope have shown the puzzling result of a D/H ratio in the upper atmosphere of Mars to be 11 times smaller than the D/H ratio in HDO and H 2 O of the lower atmosphere [Krasnopolsky et al., 1998]. One factor to explain this vertical variation was proposed: the photo-induced fractionation effect (PHIFE), due to a lower absorption cross section of solar UV of HDO compared to H 2 O [Cheng et al., 1999]. Here we suggest that in addition to PHIFE, this vertical variation of D/H ratio is also the result of preferred condensation of HDO in rising air, a process already documented in the Earth's upper stratosphere. Results of a cloud model, including condensation, sedimentation, and sublimation of icy particles in the atmosphere of Mars, are presented, supporting the efficiency of the condensation/evaporation fractionation effect (CEFE) as an important factor controlling the D/H ratio in the upper atmosphere of Mars. For a typical H 2 O profile, PHIFE provides a depletion factor of 2.5, while CEFE induces a factor of 3.5. The combined effects of PHIFE and CEFE (depletion factor of 9.5) can explain the paucity of D atoms in the upper atmosphere of Mars, implying a very low escape rate of deuterium at present and in the past and, correspondingly, a smaller quantity of H 2 O in the past.
1] We present the results of model calculations, using our new, four-species, spherical MHD model. Our results are compared with the relevant and limited available data. The resulting comparisons help us to increase our understanding of the interaction processes between the solar wind and the Martian atmosphere/ionosphere. This new model with a spherical grid structure allowed us to use small (140 km, are also consistent with the appropriate Mars Global Surveyor radio occultation electron densities. Both the calculated solar cycle maximum and solar cycle minimum total transterminator and escape fluxes are significantly smaller than our previously published values. This decrease is due to the improved temperature values used for the recombination rates in this new model, which in turn results in lower ion densities and lower fluxes.
Techniques developed for the reduction and analysis of terrestrial satellite magnetic field data are used to better understand the magnetic field observations made by Mars Global Surveyor. A global distribution of radial (Br) magnetic field observations and associated uncertainties is inverted for an equivalent source magnetization distribution and then used to generate an altitude-normalized map of Br at 200 km. The observations are well-represented by a potential function of crustal origin, consistent with a rema-nent origin for the Martian magnetic features. The correla-tion between the 40546 Br observations and Br calculated from the magnetization solution at observation locations is 0.978. For a magnetization distribution confined to a 50 km layer, calculated magnetizations range from -22 to +17 A/m. We see correlations with tectonics that were only hinted at in earlier maps. Magnetic features appear to be truncated against Valles Marineris and Ganges Chasma, suggestive of a major change in crustal properties associated with fault-ing.
This study focuses on topographic characterization of ice-associated north polar region impact craters and several enigmatic polar craterforms using new information from the Mars Orbiter Laser Altimeter (MOLA), an instrument aboard the Mars Global Surveyor (MGS) orbiter. We find that, for ice-associated craters, the topography reveals several surprising results not previously appar-ent from orbital images alone. First, geometric properties for several impact craters associated with ice and frost deposits suggest that cavity infill is as high as 80% of reconstructed, preerosion levels. Second, craters associated with ice also demonstrate unique cav-ity geometries relative to their nonpolar counterparts. Finally, in some cases, ice-associated impact features are anomalously deep, on the basis of depths modeled from the best available scaling laws. We suggest that burial of these impact features by either episodic advance of the polar cap margin or by continuous deposition at the highest rates previously estimated for the north polar region of Mars has occurred. Subsequent stripping has exhumed the features, leaving behind cavity infill deposits, and a few of these display topo-graphic levels above the surrounding preimpact surface. In at least one case, cavity interior deposits show layering with a typical thick-ness of ∼10 m, suggesting episodic deposition and ablation of ma-terials as in the polar layered terrain. In addition to ice-associated craters, we investigated the topography of several enigmatic polar craterforms. In particular, a few craterforms within ∼150 km of the permanent north polar cap appear to resemble simple, effusive lava shield volcanoes found on Earth. Their geometric properties cannot be reconciled with previous suggestions that they were manifesta-tions of martian hydromagmatic processes (i.e., maar volcanism). MOLA's initial measurements of impact craters and other crater-forms in the north polar latitudes of Mars support the concept of a geologically recent surface, with evidence of effusive volcanism and enhanced sedimentation. In addition, the measured impact crater depths for ice-associated craters suggest at least a few cases of en-hanced excavation and thus a possibly weaker target relative to the typical northern hemisphere plains.
A potential function using spherical harmonics up to degree and order 90
was derived from a selection of Mars Global Surveyor vector data. These
included all three components of those taken below 200 km altitude
during the two aerobraking phases (AB1 and AB2), the Science Phase
Orbits (SPO), and the higher-altitude (367-435 km) data taken on the
nightside during the Mapping Phase Orbits (MPO). The merger of these
sets of data provided total global coverage. The technique used was a
least squares minimization developed for Earth field analysis whereby
the relative weighting of each data source was determined by the width
of a Gaussian fit to the residual distribution about the potential
function. Also, data selection by area and area weight functions were
used to improve normalization. The residual misfit distributions for the
vertical component for different data sources are (nT) AB1, 6.5; AB2 (in
shadow), 6.7; AB2 (sunlit), 10.3; SPO, 6.4; and MPO, 5.9. The horizontal
component misfits are about the same for MPO and AB2 in shadow, but for
data taken in sunlight the scatter of horizontal component residuals
increases by 50% for AB1, a factor of two for SPO, and 30% for AB2. The
energy density spectrum evaluated at 3535 km radius (the mean altitude
of the AB and SPO data) decreased from a high of 0.2 J/km3
near n = 20 to an order of magnitude less at n = 90. Most of the power
in the spectrum lies between n = 15 and n = 40. The dipole moment was
only 8 × 1016 A . m2, which is likely close
to the noise of the coefficients. This spectrum is 40 times greater than
that of Earth at the scale sizes represented by values of n from 20 to
40. Comparisons with other published maps and models for Mars show
general agreement with the field representations at MPO altitudes, but
disagreements up to several hundred nT in components calculated for
areodetic altitudes below 200 km.
DYNAMO is a small Mars orbiter planned to be launched in 2005 or 2007, in the frame of the NASA/ CNES Mars exploration program. It is aimed at improving gravity and magnetic field resolution, in order to better understand the magnetic, geologic and thermal history of Mars, and at characterizing current atmospheric escape, which is still poorly constrained. These objectives are achieved by using a low periapsis orbit, similar to the one used by the Mars Global Surveyor spacecraft during its aerobraking phases. The proposed periapsis altitude for DYNAMO of 120–130 km, coupled with the global distribution of periapses to be obtained during one Martian year of operation, through about 5000 low passes, will produce a magnetic/gravity field data set with approximately five times the spatial resolution of MGS. Additional data on the internal structure will be obtained by mapping the electric conductivity. Low periapsis provides a unique opportunity to investigate the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, therefore atmospheric escape, which may have played a crucial role in removing atmosphere and water from the planet.
On Mars, the strong magnetization in the highland crust of the southern hemisphere and the absence of magnetic anomalies at the Hellas and Argyre impact basins have been taken as signs that the core dynamo that once drove the planet's magnetic field turned off more than 4 billion years (Gyr) ago. Here, we argue instead that the Martian dynamo turned on less than 4 Gyr ago and turned off at an unknown time since then. High spatial resolution magnetometry in both Martian hemispheres is needed to reveal the true history of the Martian dynamo.
Noble Gas Geochemistry gives a comprehensive description of the physical chemistry and cosmochemistry of noble gases, before leading on to applications for problem-solving in the earth and planetary sciences. There have been many developments in the use of the noble gases since publication of the first edition of this book in 1983. This second edition has been fully revised and updated. The book will be invaluable to graduate students and researchers in the earth and planetary sciences who use noble gas geochemistry techniques.
Using two Monte Carlo models, we have calculated the ejection of O atoms from an atomic oxygen thermosphere which is bombarded by energetic O+. In these calculations, incident oxygen ions strike atmospheric O, heating the atmosphere and setting O atoms on escape trajectories. For those ion fluxes most relevant to atmospheric sputtering at Mars, the full Monte Carlo model (DSMC model) is found to give the same sputtering yield as the Monte Carlo model in which the atmospheric structure is ignored and only the energetic atoms are tracked. In both models the sputtering yield is reduced by the electronic energy loss by the ions. The yield depends weakly on the details of the interaction potential if the relative amounts of forwardscattering to backscattering are realistic. The ejected atom energy spectra for the mean incident angle 55° are shown to be harder than the standard collision cascade distribution, close to the so-called ``incomplete cascade distribution.'' Yields for grazing incidence and for a thin atmosphere such as Europa's are given, and the analytic models used earlier are tested. Because the isotope ratios at Mars are likely to have been determined by atmospheric sputtering, Ar and Ne are included as constituents to verify the analytic models for the sputtering of trace species. The yields calculated here for an atomic O thermosphere can be used to estimate the sputtering of an atmosphere having molecules at the exobase. For Mars, ignoring feedback processes and using the ion fluxes listed by Johnson and Luhmann [1998], the loss is ~0.45 bar, of which ~0.15 bar is CO2 with the largest uncertainty for atmospheric loss being the incident ion flux.
Crustal magnetic fields on Mars are inhomogeneously distributed with the strongest fields occurring over the southern highlands in a longitude sector between approximately 130°E and 240°E. Using analytic approximations and empirical scaling laws, it is estimated that much of the weakly magnetized southern highlands (i.e., that between 110°W and 130°E) was shocked to pressures exceeding 1–2 GPa during the Hellas and Argyre impacts. Possible primary remanence carriers in the martian crust include iron oxides and iron sulfides (pyrrhotite). If pyrrhotite is the main remanence carrier, extensive demagnetization of crustal regions (∼90%) may occur at shock pressures of 2 GPa or more. Thus, at least for this remanence carrier, impact shock demagnetization can potentially explain the distribution of crustal fields in the southern highlands.
Emission phase function (EPF) observations taken in 1999–2001 by Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) support the broadest study of Martian aerosol properties to date. TES solar band and infrared (IR) spectral EPF sequences are analyzed to obtain first-time seasonal/latitudinal distributions of visible optical depths, particle sizes, and single scattering phase functions. This combined angular and wavelength coverage enables identification of two distinct ice cloud types over 45°S–45°N. Type 1 ice clouds exhibit small particle sizes (reff = 1–2 μm) and a distinctive backscattering increase. They are most prevalent in the southern hemisphere during aphelion, but also appear more widely distributed in season and latitude as topographic and high-altitude (≥20 km) ice hazes. Type 2 ice clouds exhibit larger particle sizes (reff = 3–4 μm), a distinct side-scattering minimum at 90–100° phase angles (characteristic of a change in particle shape relative to the type 1), and appear most prominently in the northern subtropical aphelion cloud belt. The majority of retrieved dust visible-to-IR optical depth ratios are indicative of reff = 1.5 ± 0.1 μm, consistent with Pathfinder and Viking/Mariner 9 reanalyses. However, increased ratios (2.7 versus 1.7) appear frequently in the northern hemisphere over LS = 50–200°, indicating substantially smaller dust particles sizes (reff = 1.0 ± 0.2 μm) at this time. In addition, larger (reff = 1.8–2.5 μm) dust particles were observed locally in the southern hemisphere during the peak of the 2001 global dust storm. Detailed spectral modeling of the TES visible band pass indicates agreement of EPF-derived dust single scattering albedos (0.92–0.94) with the spectrally resolved results from Pathfinder observations.
CO2+ dissociative recombination has been assumed in the past to proceed overwhelmingly by the channel that produces CO + O. Although the channel that leads to the products C + O2 is energetically possible, the significant rearrangement of bonds that is required has led to the belief that this channel contributes minimally. Seiersen et al. [2003] have recently measured the branching ratio for the latter channel, and they have reported a value of ∼9% of the total. We have constructed both low and high solar activity models of the Martian thermosphere, and we have tested the effect of including the C + O2 channel on the production of both thermal and escaping C atoms in the Martian atmosphere. We find that dissociative recombination of CO2+ is by far the dominant source of atomic carbon in both models, and its inclusion leads to larger densities of ambient C. The contribution of the source to the escape flux of C, however, is found to be small, both because the altitude profile of the production rate falls off rapidly near the exobase and because the O2 molecule is probably produced with considerable internal energy. A calculation of the statistical energy partitioning into vibrational and rotational energy of the product O2 molecule and the translational energy of the products of the reaction indicates that the C atom is produced with translational energy exceeding the escape energy only 3.7% of the time. The models predict that photodissociation of CO is the most important source of escaping C, as have other recent investigations. The computed escape fluxes for the minor sources, however, differ considerably from those of previous models. We find that the second most important source of escaping C is electron impact dissociation of CO, followed by dissociative recombination of CO+. The total predicted escape fluxes are comparable to those of previous models at high solar activity and are a factor of 2 larger at low solar activity.
Conjugate gradient and sparse matrix techniques are utilized in the
solution of a geomagnetic inverse problem. Global crustal data sets
collected from low-earth orbit are quickly inverted (using a design
matrix approach) or continued to a common altitude (using a normal
matrix approach) even when using parameterizations of 10,000 or more
dipoles. The sparsity results from the rapid decay of the magnetic field
with distance from the dipole. Iterative techniques such as the
conjugate gradient save computer time and space when compared to more
direct approaches using the Householder transformation, thus allowing
problems that were intractable to all but the largest supercomputers to
be performed on workstations of only moderate power.
The immense amount of the mapping-phase Mars Global Surveyor (MGS) magnetic data allows us to derive a highly accurate magnetic map of Mars. The data acquired at nighttimes within the first ~3 years of the mapping phase are divided into two almost equal parts, and each part is expressed in spherical harmonics of degree up to 90. The two models are almost identical over harmonics of degree up to 62 but show appreciable differences over higher-degree harmonics, indicating that the higher-degree harmonic coefficients have appreciable noncrustal contribution. The most repeatable components of the two models are combined to produce an accurate 62-degree harmonic model of the magnetic field of the Martian crust. It is further demonstrated that the altitude of MGS is the major limiting factor of the resolution of the mapping-phase data. The small-scale features of the data, with wavelengths shorter than ~400 km, have significant contribution from noncrustal sources. They are not useful for delineating the details of the magnetic source bodies in the crust.
The huge amount of data acquired by Mars Global Surveyor during its mapping period provides a unique opportunity to reassess the paleomagnetic pole positions of Mars previously determined on the basis of the limited low-altitude magnetic data. We identify nine small and isolated magnetic anomalies on the basis of the global magnetic maps and model each anomaly using a vertical prism of elliptical cross section. Both high-altitude (360-430 km) and low-altitude (100-200 km) magnetic data are used simultaneously. We calculate a paleomagnetic pole position assuming that the body is magnetized by a dipole core field. Although the new pole positions do not cluster as closely as the old ones, the new cluster overlaps the older cluster. The clustering suggests that Mars' rotation axis has likely wandered by ~50°-60° in the last ~4 Gyr. The number of north and south poles in the cluster suggests at least one reversal of the core field during the time the source bodies acquired magnetization.
The high-amplitude magnetic anomalies observed by the Mars Global
Surveyor imply the presence of a large intensity of magnetization in the
Martian crust. We investigate the mathematical question of determining
the distribution of magnetization that has the smallest possible
intensity, without any assumptions about the direction of magnetization.
The greatest lower bound on intensity found in this way depends on an
assumed layer thickness. An analytical expression is discovered for the
optimal magnetization, and numerical methods are described for solving
the equations that determine the distribution. Some relatively small
scale numerical calculations illustrate the theory. These calculations
enable us to conclude, for example, that if the magnetization of Mars is
confined to a 50-km thick layer, it must be magnetized with an intensity
of at least 4.76 A/m.
This paper presents a new approach for calculating the sputtering of an atmosphere by impacting particles when there are molecular species at the exobase. We couple a test particle Monte Carlo approach with a molecular dynamic model to describe the collisions between hot particles and cold molecules in the Martian atmosphere. It is shown that both the heating efficiency and sputtering by pickup ions are reduced from that in an atomic thermosphere. The yields are given for three different ratios of atoms to molecules at the exobase and are used to obtain a better estimate of the total loss of atmosphere due to the pickup ion sputtering. Using the pickup ion fluxes of Zhang et al. [1993], ~120 mbar of O and ~60 mbar of CO2 are lost. The loss of O if associated with H2O would be equivalent to ~4 m averaged over the Mars surface.
All major volcanic constructs including many Paterae and Tholi have been covered in the first period of the mission. This provides a new opportunity to better characterize most of the volcanoes in the Tharsis and Elysium region and highland volcanoes geomorphologically and chrono-stratigraphically.
The radioactive decay of 40K provides an extra source of energy to power an early dynamo; its short half-life (1.25 G.y.) ensures that the dynamo will stop early in the planet's history.
Pickup-ion-induced sputtering, a potentially important nonthermal loss mechanism for the atmosphere of Mars, will also increase the content of the oxygen corona. This atmospheric sputtering process is shown to provide a small fraction of the corona in the present epoch but is equivalent to or dominates the dissociative recombination contribution for the earlier epochs modeled by Zhang et al. (1993). The addition of sputtered atoms to the corona initiates feedback processes which can enhance the atmospheric sputtering rate in the present epoch but limits it in the earliest epoch considered. It is also shown that the sputter contribution to the corona has the same dependence on altitude as the dissociative recombination component and it may be a significant contribution during contemporary solar maximum conditions. The possible detection of the sputter-produced component of atomic O in the corona during solar maximum conditions may be the most promising way of confirming the significance of this nonthermal loss mechanism at Mars.
We have carried out Monte Carlo calculations of the velocity distributions and escape fractions for 14N and 15N released in dissociative recombination of 28N +2 and 29N +2, respectively, for a range of ion temperatures (T i) and electron temperatures (T e) appropriate to the Martian exosphere. Separate calculations were carried out for each vibrational level of N +2 for 0 ≤ v ≤ 6. We have taken into account the variation in the dissociative recombination cross section with relative velocity of the ion and electron, and the differences in the vibrational and rotational energy levels of 28N +2and 29N +2 Thè escape probabilities and ratios are found to be quite sensitive to the temperature of the N +2ions, but less so to the electron temperature or to the assumed rotational distribution. The escape probabilities for N +2 (v = 0), with T i = 400 K and T e= 2000 K and an assumed escape velocity of 4.877 kms -1, are 0.391 and 0.669 for 15N and 14N, respectively. The ratio of the escape fractions, which is a measure of the isotope differentiation effect, is 0.58. This value is close to the ratio 0.51 computed by Wallis [1978], but the individual escape fractions are smaller than his values by about a third. Sample calculations are carried out of the time evolution of the N 2 abundance and of the isotope enhancement ratio to illustrate the effect of the new computed escape probabilities. It is found that the N isotopes are still predicted to be overfractionated over the last 3.8 Gyr, but the requirements on the mechanism assumed to reduce the escape, such as the existence of a dense, early atmosphere, are reduced over those required by calculations that employ the escape fractions of Wallis.
Deuterium on Mars has been detected by the resolution of several Doppler-shifted lines ofHDO near 3.7 micrometers in the planet's
spectrum. The ratio of deuterium to hydrogen is (9 ± 4) x 10-4; the abundance of H20 was derived from lines near 1.1 micrometers. This ratio is enriched on Mars over the teiluric value by a factor of6 ± 3.
The enrichment implies that hydrogen escaped more rapidly from Mars in the past than it does now, consistent with a dense
and warm ancient atmosphere on the planet.
The most precise estimates of the elemental and isotopic composition of the martian atmosphere come from martian meteorites, in particular EETA79001. These meteorites also provide substantial evidence for at least one additional component, presumably associated with the martian interior. This evidence includes noble gases within Chassigny that are isotopically and elementally distinct from either the terrestrial or martian atmospheres, and low‐δ15N and low 40Ar/36Ar components within EETA79001. Much of the martian meteorite data can be explained by simple mixing of these two components, with some elemental fractionation generated by adsorption processes. There is no compelling evidence for additional components, although there are several hints within the data. © 1995 American Institute of Physics.
The detection of a trapped Martian atmosphere-like component in the
shergottite EETA 79001 provides the most conclusive evidence that
Shergottites, Nakhlites and Chassigny SNC meteorites are rocks from
Mars. If it is assumed that the parent body of the SNC meteorites is
indeed Mars, these meteorites can be used to estimate the abundance of
volatile elements on Mars. It is found that Mars contains a number of
volatile elements in concentrations exceeding those of the earth. The
low abundancee of primordial rare gases on Mars is explained by drastic
depletion during the escape of the early Martian atmosphere.
Zhang et al. [1993] describe some calculations of the hot atomic oxygen corona density around Mars for several solar EUV flux levels, with evolutionary effects in mind. As a part of this calculation, they used thermal upper atmosphere and photochemical equilibrium ionosphere models as input to the two-stream nonthermal exosphere computation developed by Nagy and Banks [1970]. The code results include information on the upgoing flux and energy spectrum of superthermal oxygen atoms produced by the dissociative recombination of ionospheric 02 + . Prom these, altitude profiles of the atomic oxygen corona are obtained, as are estimates of the escaping "hot" oxygen flux. The total hot oxygen escape flux can be derived by integrating the upgoing spectrum at the exobase over the energy range above the ~2 eV energy at which atomic oxygen has the escape velocity from Mars. While the altitude profiles of the coronal densities and the upgoing oxygen spectra in Figure 6 of Zhang et al. [1993] are as calculated, the results of the integrations of the escape fluxes of the atoms mentioned in the text and shown in Figure 8 are incorrect. The correct values are ,-, 6 x 1024 S -1 for the ix present EUV case, ,-, 3 x 1025 s-1 for the 3x present EUV case, and ,-, 8 x 102 for the 6x present EUV case. A corrected version of Figure 8 is given below. Of perhaps greatest concern is the impact of these revised numbers on the evolutionary calculations of Luhmann et al. [1992], who had used the erroneous values. Since the only quantity involved is the neutral atomic oxygen escape flux, no result relating to the loss from direct ion pickup from the bulk upper atmosphere including the associated ion pickup sputtering rates is affected. Moreover, because the evolutionary escape rates are heavily weighted by the latter losses in the early epoch of strongest solar EUV flux, it is estimated that the total escape rate over time obtained by Luhmann et al. [1992] is only of the order of ~15-30% larger than it should be. It is considered that this amount is much smaller than other errors inherent in the calcula
The fluxes and energy spectra of picked-up planetary O(+) ions incident on the dayside atmospheres of Venus and Mars are calculated. Maps of precipitating ion number flux and energy flux are presented which show the asymmetrical distribution of dayside energy deposition expected from this source. Although the associated heating of the atmosphere and ionosphere is found to be negligible compared to that from the usual sources, backscattered or sputtered neutral oxygen atoms are produced at energies which exceed that needed for escape from the gravitational fields of both planets. These neutral 'winds', driven by pickup ion precipitation, represent a possibly significant loss of atmospheric constituents over the age of the solar system.
Differences in chemical composition can be adduced from the different
densities of the terrestrial planets, which according to the
two-component model can be described as mixtures of a highly reduced,
volatile-free component A and an oxidized, volatiles-containing
component B. An A:B mixing ratio of 60:40 estimated for Mars compares
with an 85:15 ratio for the earth. Due to Mars' homogeneous accretion,
virtually all H2O added from component B reacted with the metallic iron
content of component A and was reduced to H2, which then escaped while
accelerating the extraction of gaseous species from the planet's
interior. Large portions of Venus and earth, but not Mars, became at
least partially molten to great depth to form vigorously convecting
mantles; gases temporarily present in the early atmospheres entered
these melts and were carried into the deep interiors.
The behavior of water and other volatiles on Mars is key to understanding the evolution of the climate. The early climate played a fundamental role in producing the observed surface morphology and possibly in enabling the existence of an early biosphere. Geochemical and isotopic data can be used to infer the history of volatiles. On the basis of the isotopic data from the atmosphere and from components of the surface (as measured in meteorites that come from Mars), there appear to be at least two reservoirs of volatiles, one that has undergone exchange with the atmosphere and has been isotopically fractionated, and a second that is unfractionated and may represent juvenile gases. The fractionation of the atmospheric component has occurred primarily through the escape of gas to space. In addition, the atmospheric gases have mixed substantially with crustal reservoirs of volatiles. Such exchange may have occurred in aqueous or hydrothermal environments. The history of escape to space, as driven by the properties of the Sun through time, is consistent with the surface geomorphology. Together, they suggest an early environment that was substantially different from the present one and the evolution through time to a colder, dryer climate.
BEFORE the Phobos mission, the magnetosphere of Mars was relatively unexplored. Basically all data on the charged-particle environment of Mars had come from the Soviet Mars missions (Mars 2, 3, 4 and 5). Here we report the results of an ion-composition experiment on board the Soviet Phobos 2 spacecraft which allowed us to determine the loss of plasma from the ionosphere of Mars. Because Mars has a very small intrinsic magnetic field, the ion outflow had been expected to be similar to that of Venus. Surprisingly, there were many similarities between the ionospheric outflow from Mars and the Earth. The ion loss from Mars results from both ion pick-up that results from mass-loading of the solar wind in the Martian boundary layer and ionospheric O+ beams of energies up to several keV, possibly from upward acceleration processes similar to those observed above the Earth's auroral oval. A preliminary estimate of the ionospheric outflow from Mars indicates that the planet is losing oxygen at a rate of ~3 x 1025 ions s-1. This corresponds to an evacuation of its present total atmospheric oxygen content (contained in CO2 and O2) in less than 100 million years.
This tutorial deals with the question of atmospheric escape on Mars. After a brief introduction describing the general context of Mars escape studies, we will present in Section 2 a simplified theory of thermal escape, of both Jeans and hydrodynamic types. The phenomenon of hydrodynamic escape, still hypothetical and not proved to have ever existed on terrestrial planets, will be treated with the help of two well known examples: (i) the isotopic fractionation of xenon in Mars and Earth atmospheres, (ii) the paradox of missing oxygen in Venus atmosphere. In Section 3, a simplified approach of non-thermal escape will be developed, treating in a specific way the different kinds of escape (photochemical escape, ion sputtering, ion escape and ionospheric outflow). As a matter of illustration, some calculations of the relative contributions of these mechanisms, and of their time evolutions, will be given, and the magnitude of the total amount of atmosphere lost by non-thermal escape will be estimated. Section 4 will present the state of knowledge concerning the constraints derived from Mars isotopic geochemistry in terms of past escape and evolution. Finally, a few conclusions, which are more interrogations, will be proposed.