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Water on Hot Rocky Exoplanets
Abstract Data suggest that most rocky exoplanets with orbital period p < 100 days (“hot” rocky exoplanets) formed as gas-rich sub-Neptunes that subsequently lost most of their envelopes, but whether these rocky exoplanets still have atmospheres is unknown. We identify a pathway by which 1–1.7 R ⊕...
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Published in: | Astrophysical journal. Letters 2021-03, Vol.909 (2), p.L22 |
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Main Authors: | , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Abstract
Data suggest that most rocky exoplanets with orbital period
p
< 100 days (“hot” rocky exoplanets) formed as gas-rich sub-Neptunes that subsequently lost most of their envelopes, but whether these rocky exoplanets still have atmospheres is unknown. We identify a pathway by which 1–1.7
R
⊕
(1–10
M
⊕
) rocky exoplanets with orbital periods of 10–100 days can acquire long-lived 10–2000 bar atmospheres that are H
2
O-dominated, with mean molecular weight >10. These atmospheres form during the planets’ evolution from sub-Neptunes into rocky exoplanets. H
2
O that is made by reduction of iron oxides in the silicate magma is highly soluble in the magma, forming a dissolved reservoir that is protected from loss so long as the H
2
-dominated atmosphere persists. The large size of the dissolved reservoir buffers the H
2
O atmosphere against loss after the H
2
has dispersed. Within our model, a long-lived, water-dominated atmosphere is a common outcome for efficient interaction between a nebula-derived atmosphere (peak atmosphere mass fraction 0.1–0.6 wt%) and oxidized magma (>5 wt% FeO), followed by atmospheric loss. This idea predicts that most rocky planets that have orbital periods of 10–100 days and that have radii within 0.1–0.2
R
⊕
of the lower edge of the radius valley still retain H
2
O atmospheres. This prediction is imminently testable with James Webb Space Telescope and has implications for the interpretation of data for transiting super-Earths. |
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ISSN: | 2041-8205 2041-8213 |
DOI: | 10.3847/2041-8213/abe7dc |