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| Format: | Preprint |
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2025
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| Online-Zugang: | https://arxiv.org/abs/2505.03200 |
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| _version_ | 1866910929514397696 |
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| author | Ito, Yuichi Kimura, Tadahiro Ohno, Kazumasa Fujii, Yuka Ikoma, Masahiro |
| author_facet | Ito, Yuichi Kimura, Tadahiro Ohno, Kazumasa Fujii, Yuka Ikoma, Masahiro |
| contents | High-precision infrared spectroscopic measurements now enable detailed characterization of sub-Neptune atmospheres, potentially providing constraints on their interiors. Motivated by this, atmospheric models have been developed to explore chemical interactions between hydrogen-dominated atmospheres and possibly underlying magma oceans with various redox states. Recent models have predicted monosilane (SiH$_4$) as a potential atmospheric species derived from magma oceans in sub-Neptunes, but suggested that it is highly depleted in the observable atmospheric layers. Here, we propose that SiH$_4$ can persist throughout the atmospheres of sub-Neptunes with FeO-free reduced magma oceans by considering the dissolution of H$_2$O into the magma oceans, a factor not accounted for in previous models. We construct a one-dimensional atmospheric model to simulate the chemical equilibrium composition of hydrogen-dominated atmospheres overlying FeO-free magma oceans, incorporating H-O-Si chemistry. Our results show that the dissolution of H$_2$O enhances the SiH$_4$ molar fraction to levels of 0.1--10~\%, preventing it from reverting to silicates in the upper atmospheric layers. We find that SiH$_4$-rich atmospheres can exist across a broad parameter space with ground temperatures of 2000--6000~K and hydrogen pressures of 10$^2$--10$^5$~bar. We discuss that SiH$_4$-rich atmospheres could contain the other silanes but lack C-/N-/O-bearing species. The detection of SiH$_4$ in future observations of sub-Neptunes would provide compelling evidence for the presence of a rocky core with a reduced magma ocean. However, the accuracy of our model is limited by the lack of data on the non-ideal behavior and radiative properties of SiH$_4$, highlighting the need for further numerical and laboratory investigations. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2505_03200 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Monosilane Worlds: Sub-Neptunes with Atmospheres Shaped by Reduced Magma Oceans Ito, Yuichi Kimura, Tadahiro Ohno, Kazumasa Fujii, Yuka Ikoma, Masahiro Earth and Planetary Astrophysics High-precision infrared spectroscopic measurements now enable detailed characterization of sub-Neptune atmospheres, potentially providing constraints on their interiors. Motivated by this, atmospheric models have been developed to explore chemical interactions between hydrogen-dominated atmospheres and possibly underlying magma oceans with various redox states. Recent models have predicted monosilane (SiH$_4$) as a potential atmospheric species derived from magma oceans in sub-Neptunes, but suggested that it is highly depleted in the observable atmospheric layers. Here, we propose that SiH$_4$ can persist throughout the atmospheres of sub-Neptunes with FeO-free reduced magma oceans by considering the dissolution of H$_2$O into the magma oceans, a factor not accounted for in previous models. We construct a one-dimensional atmospheric model to simulate the chemical equilibrium composition of hydrogen-dominated atmospheres overlying FeO-free magma oceans, incorporating H-O-Si chemistry. Our results show that the dissolution of H$_2$O enhances the SiH$_4$ molar fraction to levels of 0.1--10~\%, preventing it from reverting to silicates in the upper atmospheric layers. We find that SiH$_4$-rich atmospheres can exist across a broad parameter space with ground temperatures of 2000--6000~K and hydrogen pressures of 10$^2$--10$^5$~bar. We discuss that SiH$_4$-rich atmospheres could contain the other silanes but lack C-/N-/O-bearing species. The detection of SiH$_4$ in future observations of sub-Neptunes would provide compelling evidence for the presence of a rocky core with a reduced magma ocean. However, the accuracy of our model is limited by the lack of data on the non-ideal behavior and radiative properties of SiH$_4$, highlighting the need for further numerical and laboratory investigations. |
| title | Monosilane Worlds: Sub-Neptunes with Atmospheres Shaped by Reduced Magma Oceans |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2505.03200 |