M Godolt

German Aerospace Center (DLR), Köln, North Rhine-Westphalia, Germany

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Publications (78)64.18 Total impact

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    ABSTRACT: Motivation: The most likely places for finding life outside the Solar System are rocky planets, some of which may have surface conditions allowing for liquid water, one of the major prerequisites for life. Greenhouse gases, such as carbon dioxide (CO2), play an important role for the surface temperature and, thus, the habitability of an extrasolar planet. The amount of greenhouse gases in the atmosphere is in part determined by their outgassing from the interior. Method: We use a two-dimensional convection model to calculate partial melting and the amount of CO2 outgassed for Earth-sized stagnant-lid planets. By varying the planetary mass, we investigate the evolution of a secondary atmosphere dependent on the interior structure (different ratio of planetary to core radius). We further study the likelihood for plate tectonics depend on the interior structure and investigate the influence of plate tectonics on outgassing. Results: We find that for stagnant-lid planets the relative size of the iron core has a large impact on the production of partial melt because a variation in the interior structure changes the pressure gradient and thereby the melting temperature of silicate rocks with depth. As a consequence, for planets with a large core (a radius of at least 70%–75% of the planet's radius), outgassing from the interior is strongly reduced in comparision to a planet with the same radius but a small core. This finding suggests that the outer edge of the habitable zone of a star not only depends on the distance from the star and thus the solar influx but is further limited by small outgassing for stagnant-lid planets with a high average density, indicating a high iron content (e.g. Mercury and the recently detected exoplanets Kepler-10b and CoRoT-7b). This contradicts previous model that have assumed CO2 reservoirs being in principle unlimited for all planets. If plate tectonics is initiated, several tens of bars of CO2 can be outgassed in a short period of time – even for planets with a large iron core – and the outer boundary of the habitable zone is not influenced by the interior structure. It is, however, more difficult for planets with a thin mantle (in our test case, with a thickness of 10% of the planet's radius) to initiate plate tectonics. Our results indicate that the interior structure may strongly influence the amount of CO2 in planetary atmospheres and, thereby, the habitability of rocky planets. To obtain better constraints on the interior structure accurate measurements of size and mass are necessary.
    Planetary and Space Science 01/2014; · 2.11 Impact Factor
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    ABSTRACT: PLATO 2.0 is a mission candidate for ESA's M3 launch opportunity (2022/24). It addresses fundamental questions such as: How do planetary systems form and evolve? Are there other systems with planets like ours, able to develop life? The PLATO 2.0 instrument consists of 34 small aperture telescopes providing a wide field-of-view and a large photometric magnitude range. It targets bright stars in wide fields to detect and characterize planets down to Earth-size by photometric transits, whose masses can then be determined by ground-based radial-velocity follow-up measurements. Asteroseismology will be performed for stars <=11mag to obtain highly accurate stellar parameters, including masses and ages. The combination of bright targets and asteroseismology results in high accuracy for the bulk planet parameters: 2%, 4-10% and 10% for planet radii, masses and ages, respectively. The foreseen baseline observing strategy includes two long pointings (2-3 years) to detect and bulk characterize planets reaching into the habitable zone (HZ) of solar-like stars and an additional step-and-stare phase to cover in total about 50% of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect and characterize hundreds of small planets, and thousands of planets in the Neptune to gas giant regime out to the HZ. It will therefore provide the first large-scale catalogue of bulk characterized planets with accurate radii, masses, mean densities and ages. This catalogue will include Earth-like planets at intermediate orbital distances, where surface temperatures are moderate. Coverage of this parameter range with statistical numbers of bulk characterized planets is unique to PLATO 2.0. ...
    Experimental Astronomy 10/2013; Submitted. · 2.97 Impact Factor
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    ABSTRACT: Abstract Spectral characterization of super-Earth atmospheres for planets orbiting in the habitable zone of M dwarf stars is a key focus in exoplanet science. A central challenge is to understand and predict the expected spectral signals of atmospheric biosignatures (species associated with life). Our work applies a global-mean radiative-convective-photochemical column model assuming a planet with an Earth-like biomass and planetary development. We investigated planets with gravities of 1g and 3g and a surface pressure of 1 bar around central stars with spectral classes from M0 to M7. The spectral signals of the calculated planetary scenarios have been presented by in an earlier work by Rauer and colleagues. The main motivation of the present work is to perform a deeper analysis of the chemical processes in the planetary atmospheres. We apply a diagnostic tool, the Pathway Analysis Program, to shed light on the photochemical pathways that form and destroy biosignature species. Ozone is a potential biosignature for complex life. An important result of our analysis is a shift in the ozone photochemistry from mainly Chapman production (which dominates in Earth's stratosphere) to smog-dominated ozone production for planets in the habitable zone of cooler (M5-M7)-class dwarf stars. This result is associated with a lower energy flux in the UVB wavelength range from the central star, hence slower planetary atmospheric photolysis of molecular oxygen, which slows the Chapman ozone production. This is important for future atmospheric characterization missions because it provides an indication of different chemical environments that can lead to very different responses of ozone, for example, cosmic rays. Nitrous oxide, a biosignature for simple bacterial life, is favored for low stratospheric UV conditions, that is, on planets orbiting cooler stars. Transport of this species from its surface source to the stratosphere where it is destroyed can also be a key process. Comparing 1g with 3g scenarios, our analysis suggests it is important to include the effects of interactive chemistry. Key Words: Exoplanets-Earth-like-M-dwarf-Photochemistry-Biosignatures. Astrobiology 13, 415-438.
    Astrobiology 05/2013; 13(5):415-438. · 2.80 Impact Factor
  • 6th Alliance Week; 04/2013
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    ABSTRACT: The most interesting planetary bodies outside the Solar System regarding the search for life are potentially rocky extrasolar planets. Some of them may feature surface conditions that allow for liquid water, which is the elementary prerequisite for life as we know it. The amount of greenhouse gases, like e.g. carbon dioxide (CO2), plays an important role for the determination of the surface temperature, hence the habitability of an extrasolar planet. The amount of greenhouse gases is strongly influenced by their outgassing from the interior. In this study, we investigate under which conditions the planetary interior structure and dynamics allow for the build-up of planetary atmospheres which may lead to habitable surface conditions. We investigate the evolution of a secondary atmosphere for Earth-sized planets with different interior structures (i.e. iron-silicate mixing ratios) by applying a two-dimensional model of interior dynamics [1], which allows for the calculation of the production of partial melt [2]. From this, we estimate the amount of CO2 outgassing for Earth-sized planets with different core and mantle radii after adapting the total CO2 outgassing in 4.5 Gyr for a Venus reference simulation to the present-day atmosphere of Venus. We furthermore investigate the possible influence of plate tectonics on outgassing and the likelihood of plate tectonics depending on the interior structure of the planet. We find that the size of the iron core has a large impact on the production of partial melt, hence on the possible outgassing of CO2, which is due to the pressure-dependence of the melting temperature of silicate rocks: for planets with a large core the planetary mass is larger than for a planet with a small iron core, leading to larger melting temperatures in the upper mantle. Therefore only little outgassing from the interior can be expected. However, for the determination of the outer edge of the habitable zone it is typically assumed that enough greenhouse gas CO2 is available in the atmosphere to lead to liquid water at the surface - independent of the interior of the planet [3]. Our results on the other hand suggest that the outer boundary of the habitable zone may be constrained by the production of partial melt in the interior for planets with a large iron core and a thin silicate mantle. However, if plate tectonics initiates, several tens of bars of CO2 can be outgassed in a short time also for planets with a large iron core. In this case the outer boundary of the habitable zone would not be limited by outgassing as is the case for stagnant-lid planets. It is, however, questionable if planets with a very thin mantle are able to initiate plate tectonics. References [1] Hüttig, C. and Stemmer, K. (2008), PEPI, 171(1-4):137-146. [2] Plesa, A.-C. and Spohn, T. (2012), Transactions of the HLRS 2011, Springer, 551-565. [3] Kasting, J., Whitmire, D.P. and Reynolds, R.T. (1993), Icarus, 101:108-128.
    04/2013;
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    ABSTRACT: We find that uncertainties in the UV emissions of cool M-stars have a potentially large impact upon atmospheric biosignatures in simulations of Earth-like exoplanets i.e. planets which assume Earth's development, and biomass and a molecular nitrogen-oxygen dominated atmosphere. The stellar UV input was varied starting with a Planck curve background by up to a factor ~x100.This led to the formation of large planetary atmospheric ozone layers comparable with the Earth being calculated in our radiative-photochemical column model. Atmospheric methane, a key greenhouse gas, was significantly lowered in abundance since the increased UV stimulated hydroxyl abundance, which constitutes the main methane sink. For the highest UV scenarios, the warm, ozone-heated stratosphere led to a significant weakening in the ozone spectral band. We also investigated the effect of increasing the top-of-atmosphere incoming Lyman-alpha radiation but this had only a minimal effect on the biosignatures since it was efficiently absorbed in the uppermost planetary atmospheric layer mainly by water vapour, which was abundant being formed from methane. Methane is an important stratospheric heater which critically affects the vertical temperature gradient, hence the strength of spectral emission bands. We therefore varied methane and nitrous oxide biomass emissions, finding that a lowering in CH4 emissions by x100 compared with the Earth can influence temperature hence have a significant effect on biosignature spectral bands such as those of nitrous oxide. Our work emphasizes the need for future missions to characterize the (E)UV of cool M-dwarf stars in order to understand potential biosignature signals.
    04/2013;
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    ABSTRACT: We report here that the equation for H2O Rayleigh scattering was incorrectly stated in the original paper [arXiv:1009.5814]. Instead of a quadratic dependence on refractivity r, we accidentally quoted an r^4 dependence. Since the correct form of the equation was implemented into the model, scientific results are not affected.
    Astronomy and Astrophysics 03/2013; · 5.08 Impact Factor
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    ABSTRACT: Erdähnliche Planeten oder Supererden, bei denen man Transit‐ und Bedeckungsereignisse beobachten kann, sind für spektroskopische Untersuchungen der Atmosphäre geeignete Objekte. Es ist aber keineswegs eindeutig zu sagem, welche Bestandteile der Atmosphäre Indizien für Leben sind und wie sich diese während der Entwicklung in Milliarden von Jahren ändern. Um Instrumente zur Messung der extrasolaren Atmosphären zu entwickeln, braucht man Modellrechnungen, mit denen man die zu erwartenden Signale bei verschiedenen Sterntypen abschätzen kann.
    Physik in unserer Zeit 03/2013; 44(2):64-71.
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    ABSTRACT: We investigate the spectral appearance of Earth-like exoplanets in the HZ of different main sequence stars at different orbital distances. We furthermore discuss for which of these scenarios biomarker absorption bands may be detected during primary or secondary transit with near-future telescopes and instruments.We analyze the spectra taking into account different filter bandpasses of two photometric instruments planned to be mounted to the JWST. We analyze in which filters and for which scenarios molecular absorption bands are detectable when using the space-borne JWST or the ground-based telescope E-ELT. Absorption bands of CO2, H2O, CH4 and O3 are clearly visible in high-resolution spectra as well as in the filters of photometric instruments. However, only during primary eclipse bands of CO2, H2O and O3 are detectable for all scenarios when using photometric instruments and an E-ELT telescope setup. CH4 is only detectable at the outer HZ of the K star since here the atmospheric modeling results in very high abundances. Since the detectable CO2 and H2O bands overlap, separate bands need to be observed to prove their existence in the atmosphere. In order to detect H2O in a separate band, a S/N>7 needs to be achieved for E-ELT observations, e.g. by co-adding at least 10 transit observations. Using a spaceborne telescope like the JWST enables the detection of CO2 at 4.3mu, which is not possible for ground-based observations due to the Earth's atmospheric absorption. Hence combining observations of spaceborne and groundbased telescopes might allow to detect the presence of the biomarker molecule O3 and the related compounds H2O and CO2 in a planetary atmosphere. Other absorption bands using the JWST can only be detected for much higher S/Ns, which is not achievable by just co-adding transit observations since this would be far beyond the planned mission time of JWST.(abridged)
    Astronomy and Astrophysics 02/2013; · 5.08 Impact Factor
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    ABSTRACT: We find that variations in the UV emissions of cool M-dwarf stars have a potentially large impact upon atmospheric biosignatures in simulations of Earth-like exoplanets i.e. planets with Earth's development, and biomass and a molecular nitrogen-oxygen dominated atmosphere. Starting with an assumed black-body stellar emission for an M7 class dwarf star, the stellar UV irradiation was increased stepwise and the resulting climate-photochemical response of the planetary atmosphere was calculated. Results suggest a “Goldilocks” effect with respect to the spectral detection of ozone. At weak UV levels, the ozone column was weak (due to weaker production from the Chapman mechanism) hence its spectral detection was challenging. At strong UV levels, ozone formation is stronger but its associated stratospheric heating leads to a weakening in temperature gradients between the stratosphere and troposphere, which results in weakened spectral bands. Also, increased UV levels can lead to enhanced abundances of hydrogen oxides which oppose the ozone formation effect. At intermediate UV (i.e. with x10 the stellar UV radiative flux of black body Planck curves corresponding to spectral class M7) the conditions are “just right” for spectral detection. Results suggest that the planetary O3 profile is sensitive to the UV output of the star from ∼(200–350) nm.We also investigated the effect of increasing the top-of-atmosphere incoming Lyman-α radiation but this had only a minimal effect on the biosignatures since it was efficiently absorbed in the uppermost planetary atmospheric layer, mainly by abundant methane. Earlier studies have suggested that the planetary methane is an important stratospheric heater which critically affects the vertical temperature gradient, hence the strength of spectral emission bands. We therefore varied methane and nitrous oxide biomass emissions, finding e.g. that a lowering in methane emissions by x100 compared with the Earth can influence temperature hence have a significant effect on biosignature spectral bands such as those of nitrous oxide. Our work emphasizes the need for future missions to characterize the UVof cool M-dwarf stars in order to understand potential biosignature signals.
    Planetary and Space Science 01/2013; · 2.11 Impact Factor
  • 6th HGF Alliance Week; 01/2013
  • M. Godolt
    6th HGF Alliance Week; 01/2013
  • 11th European Workshop on Astrobiology EANA’11; 01/2013
  • Shaping E-ELT Science and Instrumentation Workshop; 01/2013
  • FNRS Contact Group Astrobiology & Planet Topers joined Meeting; 01/2013
  • Protostars and Planets VI; 01/2013
  • Physik in unserer Zeit 01/2013; 44(2013-2):64-71.
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    ABSTRACT: We present 3D atmospheric modeling results of Earthlike extrasolar planets around K- and F-type stars. So far the influence of different host stars upon Earth-like extrasolar planetary atmospheres has been investigated mainly with 1D atmospheric models. The impact of different stellar spectra and planetary orbital periods upon planetary climate and atmospheric dynamics is analyzed using a state-of-the-art 3D climate model. We find that the planetary climate strongly changes due to surface interactions. Our findings are compared to those of a 1D climate model to address the applicability of such simplified models.
    09/2012;
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    ABSTRACT: The faint young sun problem, the contradiction of a reduced solar luminosity by 15-25% during the Archean and the geologic evidence for relatively high surface temperatures that allowed the presence of liquid water, is still unresolved. It is suggested that the cooling induced by a fainter sun was e.g. offset by higher levels of greenhouse gases (GHGs) during the Archean, but the amounts of GHGs that are necessary to solve the problem can not be supported by proxy data. We present a study in which we investigate this problem by using the Chemistry Climate model EMAC (ECHAM/MESSy Atmospheric Chemistry) with a, spectrally resolved irradiance dataset valid for the Archean. As proxy for the irradiance of the young Sun at 2.5 Ga before today we use the G0V-dwarf star beta Com, which is scaled to have a total solar irradiance of 82% the present value. The EMAC model is used in a configuration with the highly resolving short-wave radiative transfer parametrization FUBRad, coupled to a mixed layer ocean, where the sea surface temperatures and the sea ice are derived from the thermodynamics of an ocean layer. We analyse the climatic impact of the spectrally resolved irradiances and other parameters representing the late Archean Earth, such as the composition of the atmosphere and the land/ocean distribution. We can show that an increase of the CO2 concentration by a factor of 10 is sufficient to obtain liquid oceans in the tropics. Further analysis concentrates on the thermal and dynamical state of the atmosphere with emphasis on the middle atmosphere.
    Planetary and Space Science 04/2012; · 2.11 Impact Factor
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    ABSTRACT: The question of habitability is very important in the context of terrestrial extrasolar planets. Generally, the Habitable Zone (HZ) is defined as the orbital region around a star, in which life-supporting (habitable) planets can exist. Taking into account that liquid water is a commonly accepted, fundamental requirement for the development of life - as we know it - the habitable region around a star is mainly determined by the stellar insolation of radiation, which is sufficient to maintain liquid water at the planetary surface. This study focuses on different processes that can lead to the complete loss of a liquid water reservoir from the surface of a terrestrial planet to determine the inner boundary of the HZ. The investigated criteria are, for example, reaching the temperature of the critical point of water at the planetary surface, the runaway greenhouse effect and the diffusion-limited escape of water from the atmosphere, which could lead to the loss of the complete water reservoir within the lifetime of a planet. We investigate these criteria, which determine the inner boundary of the HZ, with a one-dimensional radiative-convective model of a planetary atmosphere, which extends from the surface to the mid-mesosphere. Our modelling approach involves the step-by-step increase of the incoming stellar flux and the subsequent iterative calculation of resulting changes in the temperature profiles, the atmospheric water vapour content and the radiative properties. Therefore, this climate model had to be adapted to account for high temperatures and water mixing ratios. For example, the infrared radiative transfer scheme was improved to be suitable for such high temperature and pressure conditions. Modelling results are presented determining the inner boundary of the HZ affected by these processes, which can result in no liquid water on the planetary surface. In this context, especially the role of the runaway greenhouse effect is discussed in detail.
    04/2012;

Publication Stats

17 Citations
64.18 Total Impact Points

Institutions

  • 2013–2014
    • German Aerospace Center (DLR)
      • Institute of Planetary Research
      Köln, North Rhine-Westphalia, Germany
  • 2008–2012
    • Technische Universität Berlin
      • Centre of Astronomy and Astrophysics
      Berlín, Berlin, Germany