H-Atmospheres of Icy Super-Earths Formed in situ in the Outer Solar System: An Application to a Possible Planet Nine

Amit Levi, Scott J. Kenyon, Morris Podolak, Dina Prialnik
(Submitted on 3 Apr 2017)

We examine the possibility that icy super-Earth mass planets, formed over long time scales (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 which 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 ≲1010 [molec cm−2 s−1], the outgassed atmosphere has base pressure ≲ 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.

Comments:    32 pages, 11 figures, accepted to ApJ
Subjects:    Earth and Planetary Astrophysics (astro-ph.EP)
Cite as:    arXiv:1704.00400 [astro-ph.EP] (or arXiv:1704.00400v1 [astro-ph.EP] for this version)
Submission history
From: Amit Levi 
[v1] Mon, 3 Apr 2017 01:46:06 GMT (710kb,D)
https://arxiv.org/abs/1704.00400