Two Terrestrial Planet Families With Different Origins


Distinct trends in the density-radius and density-insolation planes separate the T1 (low insolation - red circles) terrestrials and the T2 (high insolation - blue squares) terrestrials. Collisions likely enhance the density of both the T1 and T2 families, while photoevaporation is likely modifying the density of sub-Neptunes (green triangles) and creating the T2 family by complete envelope stripping of some sub-Neptunes.

The important role of stellar irradiation in envelope removal for planets with diameters of <2 R⊕ has been inferred both through theoretical work and the observed bimodal distribution of small planet occurrence as a function of radius.

We examined the trends for small planets in the three-dimensional radius-insolation-density space and find that the terrestrial planets divide into two distinct families, one of which merges with terrestrial planets and small bodies in the solar system and is thus Earth-like. The other terrestrial planet family forms a bulk-density continuum with the sub-Neptunes, and is thus likely to be composed of remnant cores produced by photoevaporation. Based on the density-radius relationships, we suggest that both terrestrial families show evidence of density enhancement through collisions. Our findings highlight the important role that both photoevaporation and collisions have in determining the density of small planets.

Mark Swain, Raissa Estrela, Christophe Sotin, Gael Roudier, Robert Zellem
(Submitted on 19 Nov 2018)
Comments: 8 pages, 4 figures, Submitted to Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1811.07919 [astro-ph.EP] (or arXiv:1811.07919v1 [astro-ph.EP] for this version)
Submission history
From: Raissa Estrela
[v1] Mon, 19 Nov 2018 19:00:21 UTC (673 KB)
https://arxiv.org/abs/1811.07919
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