Secondary Atmospheres On HD 219134 b and c

We analyze the interiors of HD~219134~b and c, which are among the coolest super Earths detected thus far. Without using spectroscopic measurements, we aim at constraining if the possible atmospheres are hydrogen-rich or hydrogen-poor.

In a first step, we employ a full probabilistic Bayesian inference analysis in order to rigorously quantify the degeneracy of interior parameters given the data of mass, radius, refractory element abundances, semi-major axes, and stellar irradiation. We obtain constraints on structure and composition for core, mantle, ice layer, and atmosphere. In a second step, we aim to draw conclusions on the nature of possible atmospheres by considering atmospheric escape. Specifically, we compare the actual possible atmospheres to a threshold thickness above which a primordial (H2-dominated) atmosphere can be retained against evaporation over the planet's lifetime. The best constrained parameters are the individual layer thicknesses.

The maximum radius fraction of possible atmospheres are 0.18 and 0.13 R (radius), for planets b and c, respectively. These values are significantly smaller than the threshold thicknesses of primordial atmospheres: 0.28 and 0.19 R, respectively. Thus, the possible atmospheres of planets b and c are unlikely to be H2-dominated. However, whether possible volatile layers are made of gas or liquid/solid water cannot be uniquely determined. Our main conclusions are: (1) the possible atmospheres for planets b and c are enriched and thus possibly secondary in nature, and (2) both planets may contain a gas layer, whereas the layer of HD 219134 b must be larger. HD 219134 c can be rocky.

Caroline Dorn, Kevin Heng
(Submitted on 21 Nov 2017)

Comments: 13 pages, 10 figures, Accepted by AAS Journals
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1711.07745 [astro-ph.EP] (or arXiv:1711.07745v1 [astro-ph.EP] for this version)
Submission history
From: Caroline Dorn
[v1] Tue, 21 Nov 2017 12:26:48 GMT (3428kb,D)
https://arxiv.org/abs/1711.07745

Please follow Astrobiology on Twitter.


  • submit to reddit