Characteristics of an hybrid atmosphere with disk-captured and degassing contributions over a rocky planet’s magma ocean. A modeling approach.

Abstract

<p>Motivation:<br />   Early during their formation the planets capture an amount of atmosphere from the protoplanetary disk (Ikoma et al. 2018, Odert et al. 2018, Lammer et al. 2020, Kimura and Ikoma 2020). An additional proportion of their atmosphere is provided during the magma ocean stage by interior degassing. The latter mechanism is assumed to be the main provider of the final atmospheric mass. Its composition is compromised by the source silicate mineral and its chemical characterization (Gaillard and Scaillet 2014, Herbort et al. 2020).<br />   Numerous studies support the degassing of the oxidized gas species H<sub>2</sub>O and CO<sub>2</sub> as main contributions from the magma ocean phase (Abe and Matsui 1988, Abe 1993, Elkins-Tanton 2008, Schaefer et al. 2012, Lebrun et al. 2013, Lupu et al. 2014, Gaillard and Scaillet 2014, Salvador et al. 2017, Nikolaou et al. 2019). Previous work has also shown that H<sub>2</sub>O, in particular, plays a crucial role (Hamano et al. 2013, Katyal et al. 2019, Turbet et al. 2019) in thermal blanketing. H<sub>2</sub>O possibly leads to “long-term” (Hamano et al 2013) or “conditionally continuous” (Nikolaou et al. 2019) magma oceans that effectively cease to cool. Water also ties directly to the availability of hydrogen that drives hydrodynamic escape (Airapetian et al. 2017, Lammer et al. 2018). CO<sub>2 </sub>factors into both above processes, as well (Wordsworth and Pierrehumbert 2013, Odert et al. 2018). Constraining the H<sub>2</sub>O and CO<sub>2</sub> abundances early after formation is indispensible to the planet’s thermal evolution and extensive modeling effort has been devoted to it. Their constraint would in particular help revisit which magma ocean types among transient-conditionally continuous-permanent (Nikolaou et al. 2019) are detectable in future exoplanetary missions (ARIEL, Tinetti et al. 2018; PLATO, Rauer et al. 2014).<br /> </p> <p>Method:<br />   In this work we focus on the combination of degassed and disk-captured atmosphere under the assumption of chemical equilibrium. Using simulations from the 1D Convective Ocean of Magma Radiative Atmosphere and Degassing model (Nikolaou et al. 2019) we obtain the thermal evolution and degassing tracks of a rocky planet. In order to evaluate the chemical abundances under equilibrium conditions we employ the thermodynamical model GGchem (Woitke et al. 2018).<br />   We explore the atmospheric conditions during the lifetime of a magma ocean under varying mineral compositions and protoplanetary disk contributions. We discuss the results in the context of the likely magma ocean types.<br /> <br />A.N. and P.W. wish to thank the Erwin Schrödinger International Institute for Mathematics and Physics (ESI) of the University of Vienna, Thematic Programme on “Astrophysical Origins: Pathways from Star Formation to Habitable Planets” 2019, which enabled this collaboration.</p>