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Interior structure of Earth, Mars and the Moon, with known phase transitions for Earth and possible phase transition locations for Mars

Interior structure of Earth, Mars and the Moon, with known phase transitions for Earth and possible phase transition locations for Mars

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The Interior exploration using Seismic Investigations, Geodesy, and Heat Transport (InSight) Mission will focus on Mars’ interior structure and evolution. The basic structure of crust, mantle, and core form soon after accretion. Understanding the early differentiation process on Mars and how it relates to bulk composition is key to improving our un...

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... the sweet spot for understanding early planetary formation. The Moon's diameter limits the phase transitions in the interior to those occurring at relative shallow depths on Earth ( Khan et al. 2013;Kuskov et al. 2014), thus limiting applicability to larger bodies. Mars is large enough to be in the same pressure regime as Earth's upper mantle ( Fig. 1), small enough to be geologically arrested enough to preserve its original crust. Mars' relatively small volume also means that it contains insufficient heat producing elements to maintain vigorous present day geologic activity, thus preserving much of its original crust. Additionally, there is a wealth of data for Mars, including from ...
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... Hellas, attract cold downwellings of mantle flow. Mantle plumes underneath Tharsis and Elysium are, of course, reasonable given the volcanic activity there that has lasted until recently (e.g., Werner 2009). The figure also illustrates how the amplitudes of the thermal anomalies decrease with depth (Fig. 8) to almost vanish near the CMB (Fig. ...
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... temperature variations may affect the seismic velocities in the shallowest layers of the planet up to 400-500 km depth and hence may be detected by the SEIS instrument. Figure 10a shows the reference temperature profile calculated from averaging over longitude and latitude at constant radial distance from the center in addition to profiles for the maximum and a minimum temperature anomaly cases introduced above. The models give the same surface heat flow value of about 24 mW/m 2 and a thermal lithosphere thickness of 450 to 600 km, respectively. ...
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... deviations from the adiabat, which are observed in Fig. 10a for temperature profiles obtained by 3D thermal evolution models, are typical for convection cases with a relatively low Rayleigh number between 10 4 -10 5 (values computed using the average viscosity at the base of the stagnant lid at present day) and for pressure dependent viscosity which results in a more sluggish convection in the ...
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... Fig. 10a, the model with the largest temperature variations defining a cold end-member model shows a thermal boundary layer at the CMB of about 150 km thickness with a temperature difference across of roughly 100 K and a core-mantle heat flow of 2.8 mW/m 2 . Lower thermal boundary layers are lacking for the reference and the hot end-member ...
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... we note that our maximum temperature model is close to the model of Zharkov et al. (2009) in the lower mantle but has significantly lower temperatures in part of the upper mantle and a thicker thermal lithosphere. Figure 10b gives the temperature variations in the 3D calculations from the average as a function of radial distance from the CMB for the reference and the end-member models. It can be easily seen that the hot end-member model has the smallest lateral temperature variations. ...
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... Vacher et al. (1998) algorithm is generally thermodynamically inconsistent, but provides additional flexibility to investigate non-equilibrium scenarios or the effects of chemical changes within individual mineral phases. Figures 11 and 12 show a comparison between the outputs produced by the two methods for the Dreibus-Wänke composition (Dreibus and Wänke 1985) and the hot end-member temperature profile of . As can be observed in Fig. 12, spikes are present in both density and seismic wavespeed differences and correspond to small differences in the location of phase transitions estimated by the two codes. ...
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... additional flexibility to investigate non-equilibrium scenarios or the effects of chemical changes within individual mineral phases. Figures 11 and 12 show a comparison between the outputs produced by the two methods for the Dreibus-Wänke composition (Dreibus and Wänke 1985) and the hot end-member temperature profile of . As can be observed in Fig. 12, spikes are present in both density and seismic wavespeed differences and correspond to small differences in the location of phase transitions estimated by the two codes. Aside from these spikes, though, the difference in density values computed with the two codes is less than 50 kg/m 3 and the wavespeed difference is less than 0.2 ...
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... the majority of silicate and oxide minerals relevant to Mars' mantle, the quasiharmonic approximation of Stixrude and Lithgow- Bertelloni (2005Bertelloni ( , 2011) provides a reasonable estimate of elastic seismic velocities. Jacobs et al. (2017) show that thermodynamic Fig. 11 Temperature, pressure, density and seismic velocities profiles in the Martian mantle for a Dreibus-Wänke composition (Dreibus and Wänke 1985) associated to the hot end-member temperature profile of and computed with the two Geophysics Mineralogical codes (Vacher for Vacher et al. 1998 andPerple_X for Connolly 2005) models described ...
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... models of Mars are qualitatively similar, although modeling methods differ. The current best estimate of the radius of the Martian core (∼ 1720-1810 km, see ) has increased substantially due to the increased value of k 2 ( Konopliv et al. 2006, Fig. 13 Core radius as a function core sulfur concentration for the hot (solid curves) and cold (dashed curves) mantle temperature profile. The blue shaded area represents the core radius range in agreement with the k 2 value of Konopliv et al. (2016) and Genova et al. (2016). The acronyms stand for the different mantle mineralogy models (DW: ...
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... 2003, MA: Morgan and Anders 1979. Models agree at 1-sigma with the average moment of inertia of Mars (MOI = 0.3639 ± 0.0001) ( Konopliv et al. 2016) 2011, 2016) in comparison with Yoder et al. (2003). Overall, one of the biggest sources of uncertainty in a priori modeling of Martian structure remains the tradeoff between core density and size (Fig. ...
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... Q (Dziewo´nskiDziewo´nski and Anderson 1981). This is shown for the difference a priori reference Mars models and associated temperature structures in Fig. 14. For depth less than 300 km, all Mars models suggest a mantle colder than Earth at the same pressure, and likely larger Q. But deeper than 300 km, the Earth mantle could in contrast be colder than Mars for the same pressure, and temperature effects will reduce ...
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... SEIS. In order to illustrate the dependence of these two observables on the CMB density jump, these parameters were estimated for a wide range of interior structure models, including the 14 a priori Mars models used in a recent blind test experiment for marsquake location . The FCN period is a good indicator of the density jump as illustrated in Fig. 15a (see also Hoolst et al. 2000). It increases almost linearly with decreasing density jump at the CMB with limited spread due to different mantle mineralogy, core composition and thermal state. As observed in Fig. 15b, for epicentral distance smaller than 90 • , the seismic body wave reflection coefficients are significant only for ScSH, ...
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... in a recent blind test experiment for marsquake location . The FCN period is a good indicator of the density jump as illustrated in Fig. 15a (see also Hoolst et al. 2000). It increases almost linearly with decreasing density jump at the CMB with limited spread due to different mantle mineralogy, core composition and thermal state. As observed in Fig. 15b, for epicentral distance smaller than 90 • , the seismic body wave reflection coefficients are significant only for ScSH, ScSV, ScP and PcP. The variability in these coefficients between various models is mainly controlled by the impedance ratio at CMB. A difficulty in the analysis of body wave amplitudes is the influence of source ...
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... is mainly controlled by the impedance ratio at CMB. A difficulty in the analysis of body wave amplitudes is the influence of source radiation on these parameters. In order to remove this influence, we suggest the use of ScP over ScSV amplitude ratios. These two phases experience approximately the same radiation at the source. As observed on Fig. 15c, this ratio is dependent on the density jump at CMB, in particular for epicentral distances larger than 50 • . Since the two methods are fully independent, combining the FCN frequency and body wave amplitude ratios can strongly constrain the CMB density jump. Fig. 15 (a) Relation between density jump at the core-mantle boundary and FCN ...
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... experience approximately the same radiation at the source. As observed on Fig. 15c, this ratio is dependent on the density jump at CMB, in particular for epicentral distances larger than 50 • . Since the two methods are fully independent, combining the FCN frequency and body wave amplitude ratios can strongly constrain the CMB density jump. Fig. 15 (a) Relation between density jump at the core-mantle boundary and FCN period for the hot (solid curves) and cold (dashed curves) mantle temperature profile. See Fig. 14 and Table 4 ...
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... distances larger than 50 • . Since the two methods are fully independent, combining the FCN frequency and body wave amplitude ratios can strongly constrain the CMB density jump. Fig. 15 (a) Relation between density jump at the core-mantle boundary and FCN period for the hot (solid curves) and cold (dashed curves) mantle temperature profile. See Fig. 14 and Table 4 ...
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... joint inversion of both k 2 and ScS travel time will therefore improve greatly the determination of both the mantle structure and depth of the CMB. Figure 16 shows the differences in core size of the Reference models, detailed in Sect. 3.4 and listed in Table 4. ...
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... a recent paper, Verhoeven and Vacher (2016) have shown that the small polaron conduction, associated with charge transfer between ferrous and ferric ions, dominates the conductivity at iron and water contents relevant to the Martian mantle. Figure 17 shows the electrical conductivity profiles computed using the modeling of Verhoeven and Vacher (2016) for compositions and temperature profiles of the Martian mantle associated with the MSS models of . The electrical conductivity for the laboratory-based composition model of Bertka and Fei (1997), along with the databased profile derived by Civet and Tarits (2014) from MGS magnetic field measurements are shown for comparison. ...
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... et al. 2014). Figure 18 shows receiver functions for several given models with various epicentral distances. ...
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... discussed in Sect. 3.2.4, there is an extensive history of development of reference models for the Martian interior constrained by geodesy data and a range of geochemical and thermal models. For the InSight mission, we have selected a range of reasonable models to serve as a representative range of models ( Fig. 19 and Table 4), similar to the range of models used for the recent blind test of Marsquake location methods ( ), modified to include models from . The models can be downloaded at https://doi.org/10.5281/zenodo.1478804. The range is not meant to be an exhaustive distribution of all possible models, but rather to serve as a representative ...
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... Dreibus and Wänke (1985) chemical model. The top crustal layer is an averaged transition from regolith to consolidated rocks. The profiles of density and seismic velocities in the lower crust correspond to the mineralogical models constructed by numerical thermodynamical modeling ( Babeiko and Zharkov 1998), while the mantle S.E. Smrekar et al. Fig. 19 The set of 1D reference models defined as the reference set. Panel A shows P velocity (solid line), S velocity (dashed line), and density (dotted line) for the set of reference 1D models with line color defined as in the legend in panel B. Panel B shows shear quality factor, while panel C zooms in on the mantle structure model relies ...
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... P is the pressure in GPa and the polynomia terms values are provided in Table 5. The perturbations to FeO content are shown on Fig. 21. These are documenting: (i) the depth shift of the seismic discontinuities associated with the mineralogical transformations translate into sharp peaks, narrower than 0.5-1 GPa, and (ii) the perturbations of density and seismic velocity within the stability field of minerals. An increase of FeO content increases the density and ...

Citations

... A vast volume of information about Mars has been obtained from orbiting and landed spacecraft (Mars Pathfinder, Mars Global Surveyor, Mars Odyssey, Mars Reconnaissance Orbiter and Mars Express), and from the geodetic Doppler ranging data (Bills et al., 2005;Genova et al., 2016;Jacobson and Lainey, 2014;Konopliv et al., 2006Konopliv et al., , 2011Konopliv et al., , 2016Lainey et al., 2007;Lainey et al., 2020;Yoder et al., 2003). The Mars InSight lander touched down on the planet on November 2018, carrying on board a suite of geophysical instruments, including a seismometer, a magnetometer, a radio science experiment, and a heat flow probe to explore the planet's interior Smrekar et al., 2019). Before the recent improvements in our knowledge of the interior structure of Mars owing to the seismic measurements provided by InSight Durán et al., 2022;Knapmeyer-Endrun et al., 2021;Stähler et al., 2021), geodetic measurements used to be the sole constraint on the Martian interior. ...
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Solid body tides provide key information on the interior structure, evolution, and origin of the planetary bodies. Our Solar system harbours a very diverse population of planetary bodies, including those composed of rock, ice, gas, or a mixture of all. While a rich arsenal of geophysical methods has been developed over several years to infer knowledge about the interior of the Earth, the inventory of tools to investigate the interiors of other Solar-system bodies remains limited. With seismic data only available for the Earth, the Moon, and Mars, geodetic measurements, including the observation of the tidal response, have become especially valuable and therefore, has played an important role in understanding the interior and history of several Solar system bodies. To use tidal response measurements as a means to obtain constraints on the interior structure of planetary bodies, appropriate understanding of the viscoelastic reaction of the materials from which the planets are formed is needed. Here, we review the fundamental aspects of the tidal modeling and the information on the present-day interior properties and evolution of several planets and moons based on studying their tidal response. We begin with an outline of the theory of viscoelasticity and tidal response. Next, we proceed by discussing the information on the tidal response and the inferred structure of Mercury, Venus, Mars and its moons, the Moon, and the largest satellites of giant planets, obtained from the analysis of the data that has been provided by space missions. We also summarise the upcoming possibilities offered by the currently planned missions.
... Exploration is made for Q S ranging from 160 and 670 with step of 25 (equivalent to Q P ranging from 360 to 1500, with step of 57). It includes the effective Q~300 proposed by Giardini et al (2020) for LF events at distances ranging from 25 to 45 ∘ as well as Mars a priori Q μ (Smrekar et al, 2018;Lognonné and Mosser, 1993). ...
Article
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Since early 2019, the InSight mission has proven that Mars is seismically active, with more than 900 seismic events recorded. Among them, several events have characteristics close to terrestrial tectonic earthquakes. Most of these events are located on the major graben system of Cerberus Fossae and, a little further north, on the secondary system of Grjotá Valles. In this study, we invert the seismic moment tensors for nine of these tectonic marsquakes characterized by high quality data. Seven of them are located on Cerberus Fossae/Grjotá Valles and two of them are located near the Martian dichotomy. The moment tensors allow us to interpret the nature and depth of the seismic sources at the origin of these events. In our approach, we invert the P and S body waveforms, the PP, SS, PPP and SSS secondary phase maximum amplitudes and we look for solutions with surface waves weaker than the Martian noise. From our results on moment tensors, we determine that all our events have been triggered at moderate depths of 15-36 km. We deduce that the seven events located on Cerberus Fossae have geometries similar to the fractures and are generated by tectonics. This activity is supposed to result from the reactivation of previous faults and fractures, which would have been initially induced by the propagation of volcanic dikes at depth. The two dichotomy events are due to deep compressive fracturing of the Martian lowlands. They are therefore triggered by the planetary thermal contraction. Our results are in strong agreement with recent studies on the event depths and on the previous moment tensors calculated for two events.
... An indication that substantial magnetization is carried at these smaller spatial scales is the surface field strength at the InSight landing site: the measured~2000 nT ( Figure 3), is about an order of magnitude larger than predictions from models based on satellite data (Mittelholz et al., 2018a;Smrekar et al., 2018;Johnson et al., 2020). Even comparisons among data from different satellite altitudes show the effect of resolving shorter wavelength structure. ...
Article
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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.
... We consider the 1-dimensional density profiles of the mantle and core of Mars that were developed in Smrekar et al. (2019) and later expanded upon in Knapmeyer-Endrun et al. (2021). Our approach does not make use of the predicted density profile in the crust from these models, and the exact value of the core radius has little impact on our global crustal thickness models. ...
... We thus neglected a few models that differ only in how they treat the crust, and we chose that model whose core radius was closest to the InSight core radius of Stähler et al. (2021). Following the procedure described in Smrekar et al. (2019), we also constructed a model that is based on the best-fitting bulk silicate composition of Khan et al. (2022), the core radius of Stähler et al. (2021), and the temperature profile of Knapmeyer-Endrun et al. (2021). Unlike the other 1-dimensional models that assumed a bulk silicate composition based on Martian meteorite data, this model (henceforth referred to as Khan2022) was developed to satisfy the InSight seismic constraints with only limited cosmochemical assumptions. ...
... Without such a filter, either noise in the gravity field or imperfect modeling of the contributions in Equation A5 would give rise to unrealistic oscillations of the function h. This filter is designed to have an amplitude of 0.5 at degree 50, which is a choice used by previous investigations (e.g., Baratoux et al., 2014;Smrekar et al., 2019;Wieczorek et al., 2019). ...
Article
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Analyses of seismic data from the InSight mission have provided the first in situ constraints on the thickness of the crust of Mars. These crustal thickness constraints are currently limited to beneath the lander that is located in the northern lowlands, and we use gravity and topography data to construct global crustal thickness models that satisfy the seismic data. These models consider a range of possible mantle and core density profiles, a range of crustal densities, a low‐density surface layer, and the possibility that the crustal density of the northern lowlands is greater than that of the southern highlands. Using the preferred InSight three‐layer seismic model of the crust, the average crustal thickness of the planet is found to lie between 30 and 72 km. Depending on the choice of the upper mantle density, the maximum permissible density of the northern lowlands and southern highlands crust is constrained to be between 2,850 and 3,100 kg m⁻³. These crustal densities are lower than typical Martian basaltic materials and are consistent with a crust that is on average more felsic than the materials found at the surface. We argue that a substantial portion of the crust of Mars is a primary crust that formed during the initial differentiation of the planet. Various hypotheses for the origin of the observed intracrustal seisimic layers are assessed, with our preferred interpretation including thick volcanic deposits, ejecta from the Utopia basin, porosity closure, and differentiation products of a Borealis impact melt sheet.
... B efore NASA's InSight mission 1 , Mars' size, mass, and moment of inertia provided initial estimates of its internal structure 2,3 . Additional constraints on Martian crustal and mantle structure have been available from meteorites, satellite probes, and direct sampling from the surface probes [4][5][6] . ...
Article
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Marsquakes excite seismic wavefield, allowing the Martian interior structures to be probed. However, the Martian seismic data recorded by InSight have a low signal-to-noise ratio, making the identification of marsquakes challenging. Here we use the Matched Filter technique and Benford’s Law to detect hitherto undetected events. Based on nine marsquake templates, we report 47 newly detected events, >90% of which are associated with the two high-quality events located beneath Cerberus Fossae. They occurred at all times of the Martian day, thus excluding the tidal modulation (e.g., Phobos) as their cause. We attribute the newly discovered, low-frequency, repetitive events to magma movement associated with volcanic activity in the upper mantle beneath Cerberus Fossae. The continuous seismicity suggests that Cerberus Fossae is seismically highly active and that the Martian mantle is mobile.
... The average surface heat flow on Mars has been estimated to be not much more than 25 mW=m 2 (e.g., Grott et al., 2012;Plesa et al., 2016Plesa et al., , 2018Smrekar et al., 2018). For a thermal conductivity of the order of 10 À2 W=mK, the expected temperature gradient will then be not more than a few Kelvin per meter. ...
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The NASA InSight lander mission to Mars payload includes the Heat Flow and Physical Properties Package HP³ to measure the surface heat flow. The package was designed to use a small penetrator - nicknamed the mole - to implement a vertical string of temperature sensors in the soil to a depth of 5 m. The mole itself is equipped with sensors to measure a thermal conductivity- depth profile as it proceeds to depth. The heat flow is calculated from the product of the temperature gradient and the thermal conductivity. To avoid the perturbation caused by annual surface temperature variations, the measurements need to be taken at a depth between 3 m and 5 m. The mole is designed to penetrate cohesionless soil similar in rheology to quartz sand which is expected to provide a good analogue material for Martian sand. The sand would provide friction to the buried mole hull to balance the remaining recoil of the mole hammer mechanism that drives the mole forward. Unfortunately, the mole did not penetrate more than roughly a mole length of 40 cm. The failure to penetrate deeper is largely due to a cohesive duricrust of a few tens of centimeter thickness that failed to provide the required friction. Although a suppressor mass and spring as part of the mole hammer mechanism absorb much of the recoil, the available mass did not allow designing a system that fully eliminated the recoil. The mole penetrated to 40 cm depth benefiting from friction provided by springs in the support structure from which it was deployed and from friction and direct support provided by the InSight Instrument Deployment Arm. In addition, the Martian soil provided unexpected levels of penetration resistance that would have motivated designing a more powerful mole. The low weight of the mole support structure was not sufficient to guide the mole penetrating vertically. Roughly doubling the overall mass of the instrument package would have allowed to design a more robust system with little or no recoil, more energy of the mole hammer mechanism and a more massive support structure. In addition, to cope with duricrust a mechanism to support the mole to a depth of about two mole lengths should be considered.
... Most recently, Mars has been the target of a dedicated geophysical observatory mission, InSight , that placed an extremely sensitive seismometer with broadband and short period sensors on the surface of the planet. It also enabled highly accurate measurements of the rotation axis, of the local-small scale-magnetic field and its time variation and of atmosphere pressure, temperature and wind speed (Banfield et al. 2019;Folkner et al. 2018;Lognonne et al. 2019) and of the thermal and mechanical properties of the Martian soil Spohn et al. 2021a) and interior (Lognonne et al. 2020;Giardini et al. 2020;Knappmeyer-Endrun et al. 2021;Khan et al. 2021;Stähler et al. 2021. Unfortunately, attempts to emplace thermal sensors at the required depth of 3-5 m were not successful and the goal of measuring for the first time the heat flow from another terrestrial planet had to be abandoned. ...
... They can be resonant with a rotational normal mode related to an internal global fluid layer and therefore their observation can be used to infer the existence and properties of such a fluid layer. This is particularly relevant for Mars, for which nutation observations by the InSight and ExoMars 2022 missions will constrain the core radius and density and inform on the existence of an inner core (e.g., Dehant et al. 2000Dehant et al. , 2020Smrekar et al. 2019). For bodies in a spin-orbit resonance, dissipation drives the spin axis to an equilibrium orientation in which the angle between the spin pole and the orbit normal, the obliquity, is nearly constant and determined by a balance between the precession of the orbit and precessional reaction of the planet or satellite (Williams et al. 2001;Bills 2005). ...
... Most recently, in January 2019, the InSight mission ) installed a highly sophisticated seismometer on Mars with ultra-sensitive short period and broad band three component sensors (Lognonne et al. 2019;Lognonne et al. 2020). As a single station, the InSight seismometer cannot uniquely locate seismic events. ...
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The Earth-like planets and moons in our solar system have iron-rich cores, silicate mantles, and a basaltic crust. Differentiated icy moons can have a core and a mantle and an outer water–ice layer. Indirect evidence for several icy moons suggests that this ice is underlain by or includes a water-rich ocean. Similar processes are at work in the interiors of these planets and moons, including heat transport by conduction and convection, melting and volcanism, and magnetic field generation. There are significant differences in detail, though, in both bulk chemical compositions and relative volume of metal, rock and ice reservoirs. For example, the Moon has a small core [~ 0.2 planetary radii ( R P )], whereas Mercury’s is large (~ 0.8 R P ). Planetary heat engines can operate in somewhat different ways affecting the evolution of the planetary bodies. Mercury and Ganymede have a present-day magnetic field while the core dynamo ceased to operate billions of years ago in the Moon and Mars. Planets and moons differ in tectonic style, from plate-tectonics on Earth to bodies having a stagnant outer lid and possibly solid-state convection underneath, with implications for their magmatic and atmosphere evolution. Knowledge about their deep interiors has improved considerably thanks to a multitude of planetary space missions but, in comparison with Earth, the data base is still limited. We describe methods (including experimental approaches and numerical modeling) and data (e.g., gravity field, rotational state, seismic signals, magnetic field, heat flux, and chemical compositions) used from missions and ground-based observations to explore the deep interiors, their dynamics and evolution and describe as examples Mercury, Venus, Moon, Mars, Ganymede and Enceladus.
... Satellite missions to Mars have resulted in several orbital models of the global magnetic field, reviewed recently by Smrekar et al. (2018). Here, we use the most recent one of Langlais et al. (2019), which has resolution around 150 km. ...
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Plain Language Summary Four billion years ago Mars had a magnetic field generated by a dynamo operating in its liquid core, as Earth has today. It cooled faster than Earth and dynamo action ceased but not before it had magnetized the planet's crust. This study is made topical by the arrival of the Chinese rover Zhurong, which is capable of carrying out a ground magnetic survey. The lander InSight recorded a magnetic field some 10 times stronger than expected from measurements made by satellite in orbit. Here we use a relatively new technique to separate proposed magnetic structures into their “invisible” and “visible” parts. We show this while the magnetic field is stronger in the Southern Hemisphere than the North, this does not imply one hemisphere is more strongly magnetized than the other. Strong ground measurements can be explained by a strongly magnetized, invisible, shell that has been broken up into smaller, visible, fragments. Larger impact craters have no magnetic anomaly, an observation often attributed to removal of the original magnetized material; we show the anomaly remains if the surrounding crust is strongly magnetized and propose the source of the anomalies lies deeper than the bottom of these craters.
... The average surface heat flow on Mars has been estimated to be not much more than 25 / % (e.g., Grott et al., 2012;Plesa et al., 2016Plesa et al., , 2018Smrekar et al., 2018). For a thermal conductivity of the order of 10 &% ⁄ , the expected temperature gradient will then be not more than a few Kelvin per meter. ...
Preprint
The NASA InSight mission payload includes the Heat Flow and Physical Properties Package HP^3 to measure the surface heat flow. The package was designed to use a small penetrator - nicknamed the mole - to implement a string of temperature sensors in the soil to a depth of 5m. The mole itself is equipped with sensors to measure a thermal conductivity as it proceeds to depth. The heat flow would be calculated from the product of the temperature gradient and the thermal conductivity. To avoid the perturbation caused by annual surface temperature variations, the measurements would be taken at a depth between 3 m and 5 m. The mole was designed to penetrate cohesionless soil similar to Quartz sand which was expected to provide a good analogue material for Martian sand. The sand would provide friction to the buried mole hull to balance the remaining recoil of the mole hammer mechanism that drives the mole forward. Unfortunately, the mole did not penetrate more than a mole length of 40 cm. The failure to penetrate deeper was largely due to a few tens of centimeter thick cohesive duricrust that failed to provide the required friction. Although a suppressor mass and spring in the hammer mechanism absorbed much of the recoil, the available mass did not allow a system that would have eliminated the recoil. The mole penetrated to 40 cm depth benefiting from friction provided by springs in the support structure from which it was deployed. It was found in addition that the Martian soil provided unexpected levels of penetration resistance that would have motivated to designing a more powerful mole. It is concluded that more mass would have allowed to design a more robust system with little or no recoil, more energy of the mole hammer mechanism and a more massive support structure.
... The experimental results along the areotherm Case 12 are also compared to mantle velocity models (Smrekar et al., 2019) computed along the same areotherm using the thermodynamic approach detailed above (Figure 3a). Several bulk chemistry compositions proposed for the mantle of Mars are considered here-MA: Morgan & Anders, 1979;LF: Lodders & Fegley, 1997;EH45 and EH70: Sanloup et al., 1999;MM: Mohapatra & Murty, 2003;TA: Taylor, 2013;and YO: Yoshizaki & McDonough, 2020; together with the bulk chemistry of our starting material (Table 1). ...
Article
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Plain Language Summary The InSight mission operating on Mars is currently monitoring the planet's seismic activity. The recorded marsquakes can be used to obtain information on Mars' internal composition. However, the interpretation of these observations requires knowledge of the physical properties of the minerals expected to compose the Martian mantle at the relevant conditions. In this study we report: (1) experiments investigating the nature and abundance of the mineral phases stable at Martian mantle conditions; (2) sound velocity and density measurements on these rocks over a pressure and temperature range directly relevant for Mars' mantle, providing information that can be directly compared to the seismological findings from the InSight mission. Our results reveal the stability of small amounts of magnetite, an Fe³⁺‐rich mineral not reported in previous studies but a likely candidate in Mars' oxidized mantle environment. Moreover, measured wave velocities indicate the existence of a region between 150 and 350 km depth where, due to large temperature‐induced reduction, shear wave velocities decrease with depth as opposed to an expected increase. This finding is consistent with recent observations from the InSight mission on Mars.