<p>Liquid water is generally assumed to be the most important factor for the emergence of life, and so a major goal in exoplanet science is the search for planets with water oceans. On terrestrial planets, the silicate mantle is a large source of water, which can be outgassed into the atmosphere via volcanism. Outgassing is subject to a series of feedback processes between atmosphere and interior, which continually shape both atmospheric composition, pressure, and temperature, as well as interior dynamics. For example, water has a high solubility in surface lava, which can strongly limit its outgassing into the atmosphere even at low atmospheric pressures. In contrast, CO<sub>2</sub> can be easily outgassed. This drives up the surface pressure and temperature, potentially preventing further water outgassing [1].</p>
<p>We present the results of an extensive parameter study, where we use a newly developed 1D numerical model to simulate the coupled evolution of the atmosphere and interior of terrestrial exoplanets up to 5 Earth masses around Sun-like stars, with internal structures ranging from Moon- to Mercury-like. The model accounts for the main mechanisms controlling the global-scale, long-term evolution of stagnant-lid rocky planets (i.e. bodies without plate tectonics), and it includes a large number of atmosphere-interior feedback processes, such as a CO<sub>2</sub> weathering cycle, volcanic outgassing based on the pressure-dependent solubility of volatiles in surface lava, a water cycle between ocean and atmosphere, greenhouse heating, as well as the influence of a primordial H<sub>2</sub> atmosphere, which can be lost through escape processes. While many atmosphere-interior feedback processes have been studied before in detail (e.g. [2, 3]), we present here a comprehensive model combining the important planetary processes across a wide range of terrestrial planets.</p>
<p>We find that a significant majority of high-density exoplanets (i.e. Mercury-like planets with large cores) are able to outgas and sustain water on their surface. In contrast, most planets with intermediate, Earth-like densities either transition into a runaway greenhouse regime due to strong CO<sub>2</sub> outgassing, or retain part of their primordial atmosphere, which prevents water from being outgassed. This suggests that high-density planets could be the most promising targets when searching for suitable candidates for hosting liquid water. Furthermore, the degeneracy of the interior structures of high-density planets is limited compared to that of planets with Earth-like density, which further facilitates the characterization of these bodies, and our results predict largely uniform atmospheric compositions across the range of high-density planets, which could be verified by future spectroscopic measurements.</p>
<p>&#160;</p>
<p>References:</p>
<p>[1] Tosi, N. <em>et al.</em> The habitability of a stagnant-lid earth. <em>A&A</em> <strong>605</strong>, A71 (2017).</p>
<p>[2] Noack, L., Rivoldini, A. & Van Hoolst, T. Volcanism and outgassing of stagnant-lid planets: Implications for the habitable zone. <em>Physics of the Earth and Planetary Interiors</em> <strong>269</strong>, 40&#8211;57 (2017).</p>
<p>[3] Foley, B. J. & Smye, A. J. Carbon Cycling and Habitability of Earth-Sized Stagnant Lid Planets. <em>Astrobiology</em> <strong>18</strong>, 873&#8211;896 (2018).</p>
Pedogenic processes and the drying of Mars
