TY - JOUR
T1 - H-atmospheres of Icy Super-Earths Formed in Situ in the Outer Solar System
T2 - An Application to a Possible Planet Nine
AU - Levi, A.
AU - Kenyon, S. J.
AU - Podolak, M.
AU - Prialnik, D.
N1 - Publisher Copyright:
© 2017. The American Astronomical Society. All rights reserved.
PY - 2017/4/20
Y1 - 2017/4/20
N2 - We examine the possibility that icy super-Earth mass planets, formed over long timescales (0.1-1 Gyr) at large distances (∼200-1000 au) from their host stars, will develop massive H-rich atmospheres. Within the interior of these planets, high pressure converts CH4 into ethane, butane, or diamond and releases H2. Using simplified models that capture the basic physics of the internal structure, we show that the physical properties of the atmosphere depend on the outflux of H2 from the mantle. When this outflux is molec cm-2 s-1, the outgassed atmosphere has a base pressure of ≲1 bar. Larger outflows result in a substantial atmosphere where the base pressure may approach 103-104 bar. For any pressure, the mean density of these planets, 2.4-3 g cm-3, is much larger than the mean density of Uranus and Neptune, 1.3-1.6 g cm-3. Thus, observations can distinguish between a Planet Nine with a primordial H/He-rich atmosphere accreted from the protosolar nebula and one with an atmosphere outgassed from the core.
AB - We examine the possibility that icy super-Earth mass planets, formed over long timescales (0.1-1 Gyr) at large distances (∼200-1000 au) from their host stars, will develop massive H-rich atmospheres. Within the interior of these planets, high pressure converts CH4 into ethane, butane, or diamond and releases H2. Using simplified models that capture the basic physics of the internal structure, we show that the physical properties of the atmosphere depend on the outflux of H2 from the mantle. When this outflux is molec cm-2 s-1, the outgassed atmosphere has a base pressure of ≲1 bar. Larger outflows result in a substantial atmosphere where the base pressure may approach 103-104 bar. For any pressure, the mean density of these planets, 2.4-3 g cm-3, is much larger than the mean density of Uranus and Neptune, 1.3-1.6 g cm-3. Thus, observations can distinguish between a Planet Nine with a primordial H/He-rich atmosphere accreted from the protosolar nebula and one with an atmosphere outgassed from the core.
KW - planets and satellites: atmospheres
KW - planets and satellites: composition
KW - planets and satellites: formation
KW - planets and satellites: interiors
KW - planets and satellites: tectonics
UR - http://www.scopus.com/inward/record.url?scp=85018988223&partnerID=8YFLogxK
U2 - 10.3847/1538-4357/aa6ba6
DO - 10.3847/1538-4357/aa6ba6
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AN - SCOPUS:85018988223
SN - 0004-637X
VL - 839
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 111
ER -