14:45 〜 15:00
[PCG19-15] Silane: Magma-derived gas of super-Earth with reduced rocky core and hydrogen-rich atmosphere
キーワード：系外惑星、マグマオーシャン、大気
From previous exoplanet exploration, more than 1000 super-Earths have been discovered. Now, we have entered a new era of detailed characterisation of super-Earths, as exemplified by atmospheric observations of super-Earths using the James Webb Space Telescope (JWST). In addition to JWST, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey (Ariel) mission, scheduled for launch in 2029, will conduct a high-precision, wide-wavelength survey of exoplanet atmospheres, from Jupiter-like to Earth-like planets, which is expected to dramatically improve our understanding of super-Earths in the future.
Planets with thick hydrogen-rich atmospheres and rocky cores are expected to be one main type of super-Earths. The strong blanketing effect of the thick hydrogen-rich atmospheres of such super-Earths can make the rocky surface hot enough to melt and vaporize; then, the vaporized rock gas would alter the composition of the hydrogen-rich atmosphere. Thus, detecting this magma-derived atmospheric composition could provide a piece of evidence that the super-Earth with a thick hydrogen-rich atmosphere has a rocky core. While previous studies focused on oxidised (iron oxide-containing) magmas like Earth and found that the oxidized magmas can react with hydrogen-rich atmospheres to produce large amounts of water (Ikoma & Genda 2006, Kite et al. 2020), reduced (iron oxide-free) rock such as Enstatite can be another possibility in rocky cores of super-Earths.
In this study, we investigate the atmospheric composition of hydrogen-rich atmospheres in contact with underlying iron oxide-free magma oceans of super-Earths based on the gas and melt chemical equilibrium calculations of the Si-O-H chemical systems. From the chemical equilibrium calculations, we show that a unique species, silane (SiH4), can be abundant thorough the reaction between SiO evaporated from magma and H2 in the atmospheres. Then, we show that the dissolution of H2O, another molecule produced in the reaction between SiO and H2, into the magma occurs, producing more SiH4 due to the decrease in the amount of H2O. Finally, we will present the conditions under which large amounts of SiH4 are produced and discuss the atmospheric spectra of super-Earths in such cases.
Planets with thick hydrogen-rich atmospheres and rocky cores are expected to be one main type of super-Earths. The strong blanketing effect of the thick hydrogen-rich atmospheres of such super-Earths can make the rocky surface hot enough to melt and vaporize; then, the vaporized rock gas would alter the composition of the hydrogen-rich atmosphere. Thus, detecting this magma-derived atmospheric composition could provide a piece of evidence that the super-Earth with a thick hydrogen-rich atmosphere has a rocky core. While previous studies focused on oxidised (iron oxide-containing) magmas like Earth and found that the oxidized magmas can react with hydrogen-rich atmospheres to produce large amounts of water (Ikoma & Genda 2006, Kite et al. 2020), reduced (iron oxide-free) rock such as Enstatite can be another possibility in rocky cores of super-Earths.
In this study, we investigate the atmospheric composition of hydrogen-rich atmospheres in contact with underlying iron oxide-free magma oceans of super-Earths based on the gas and melt chemical equilibrium calculations of the Si-O-H chemical systems. From the chemical equilibrium calculations, we show that a unique species, silane (SiH4), can be abundant thorough the reaction between SiO evaporated from magma and H2 in the atmospheres. Then, we show that the dissolution of H2O, another molecule produced in the reaction between SiO and H2, into the magma occurs, producing more SiH4 due to the decrease in the amount of H2O. Finally, we will present the conditions under which large amounts of SiH4 are produced and discuss the atmospheric spectra of super-Earths in such cases.