M Godolt

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

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Publications (82)65.7 Total impact

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    ABSTRACT: Ocean planets are volatile-rich planets, not present in our Solar system, which are thought to be dominated by deep, global oceans. This results in the formation of high-pressure water ice, separating the planetary crust from the liquid ocean and, thus, also from the atmosphere. Therefore, instead of a carbonate–silicate cycle like on the Earth, the atmospheric carbon dioxide concentration is governed by the capability of the ocean to dissolve carbon dioxide (CO2). In our study, we focus on the CO2 cycle between the atmosphere and the ocean which determines the atmospheric CO2 content. The atmospheric amount of CO2 is a fundamental quantity for assessing the potential habitability of the planet's surface because of its strong greenhouse effect, which determines the planetary surface temperature to a large degree. In contrast to the stabilizing carbonate–silicate cycle regulating the long-term CO2 inventory of the Earth atmosphere, we find that the CO2 cycle feedback on ocean planets is negative and has strong destabilizing effects on the planetary climate. By using a chemistry model for oceanic CO2 dissolution and an atmospheric model for exoplanets, we show that the CO2 feedback cycle can severely limit the extension of the habitable zone for ocean planets.
    Monthly Notices of the Royal Astronomical Society 07/2015; 452(4). DOI:10.1093/mnras/stv1487 · 5.11 Impact Factor
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    ABSTRACT: Ozone is an important radiative trace gas in the Earth's atmosphere. The presence of ozone can significantly influence the thermal structure of an atmosphere, and by this e.g. cloud formation. Photochemical studies suggest that ozone can form in carbon dioxide-rich atmospheres. We investigate the effect of ozone on the temperature structure of simulated early Martian atmospheres. With a 1D radiative-convective model, we calculate temperature-pressure profiles for a 1 bar carbon dioxide atmosphere. Ozone profiles are fixed, parameterized profiles. We vary the location of the ozone layer maximum and the concentration at this maximum. The maximum is placed at different pressure levels in the upper and middle atmosphere (1-10 mbar). Results suggest that the impact of ozone on surface temperatures is relatively small. However, the planetary albedo significantly decreases at large ozone concentrations. Throughout the middle and upper atmospheres, temperatures increase upon introducing ozone due to strong UV absorption. This heating of the middle atmosphere strongly reduces the zone of carbon dioxide condensation, hence the potential formation of carbon dioxide clouds. For high ozone concentrations, the formation of carbon dioxide clouds is inhibited in the entire atmosphere. In addition, due to the heating of the middle atmosphere, the cold trap is located at increasingly higher pressures when increasing ozone. This leads to wetter stratospheres hence might increase water loss rates on early Mars. However, increased stratospheric H2O would lead to more HOx, which could efficiently destroy ozone. This result emphasizes the need for consistent climate-chemistry calculations to assess the feedback between temperature structure, water content and ozone chemistry. Furthermore, convection is inhibited at high ozone amounts, leading to a stably stratified atmosphere.
    Icarus 05/2015; 257. DOI:10.1016/j.icarus.2015.05.028 · 3.04 Impact Factor
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    ABSTRACT: The potential habitability of a terrestrial planet is usually defined by the possible existence of liquid water on its surface, since life as we know it needs liquid water at least during a part of its life cycle. The potential presence of liquid water on a planetary surface depends on many factors such as, most importantly, surface temperatures. The properties of the planetary atmosphere and its interaction with the radiative energy provided by the planet's host star are thereby of decisive importance.
    Planetary and Space Science 03/2015; 111(1). DOI:10.1016/j.pss.2015.03.010 · 1.88 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 10/2014; 38:249. DOI:10.1007/s10686-014-9383-4 · 1.99 Impact Factor
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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 08/2014; 98. DOI:10.1016/j.pss.2014.01.003 · 1.88 Impact Factor

  • Towards Other Earths II; 01/2014
  • M. Godolt ·

    Besichtigung des DLR durch PGzB; 01/2014
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    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 one bar around central stars with spectral classes from M0 to M7. The spectral signals of the calculated planetary scenarios have been presented by Rauer et al. (2011). 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 the terrestrial 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.
    Astrobiology 05/2013; 13(5):415-438. DOI:10.1089/ast.2012.0926 · 2.59 Impact Factor
  • L. Noack · M. Godolt · P. von Paris · A.-C. Plesa · B. Stracke · D. Breuer ·

    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.
    EGU General Assembly; 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.
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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; DOI:10.1051/0004-6361/201015329e · 4.38 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. DOI:10.1002/piuz.201301320
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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; 553. DOI:10.1051/0004-6361/201117723 · 4.38 Impact Factor
  • M Godolt · H Rauer · Consortium Plato ·

    FNRS Contact Group Astrobiology & Planet Topers joined Meeting; 01/2013

  • Protostars and Planets VI; 01/2013
  • J L Grenfell · S Gebauer · P von Paris · M Godolt · H Rauer ·

    6th HGF Alliance Week; 01/2013
  • R. Titz-Weider · S Gebauer · M Godolt · J L Grenfell ·

    Physik in unserer Zeit 01/2013; 44(2013-2):64-71.

  • 11th European Workshop on Astrobiology EANA’11; 01/2013
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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 Earths 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 about(200-350) nm. 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 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.
    Planetary and Space Science 01/2013; 98. DOI:10.1016/j.pss.2013.10.006 · 1.88 Impact Factor

Publication Stats

195 Citations
65.70 Total Impact Points


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