The formation of mini-Neptunes

Julia Venturini, Ravit Helled
(Submitted on 14 Sep 2017)

Mini-Neptunes seem to be common planets. In this work we investigate the possible formation histories and predicted occurrence rates of mini-Neptunes assuming the planets form beyond the iceline. We consider pebble and planetesimal accretion accounting for envelope enrichment and two different opacity conditions. We find that the formation of mini-Neptunes is a relatively frequent output when envelope enrichment by volatiles is included, and that there is a “sweet spot” for mini-Neptune formation with a relatively low solid accretion rate of ~10^{-6} Earth masses per year. This rate is typical for low/intermediate-mass protoplanetary disks and/or disks with low metallicities. With pebble accretion, envelope enrichment and high opacity favor the formation of mini-Neptunes, with more efficient formation at large semi-major axes (~30 AU) and low disk viscosity. For planetesimal accretion, such planets can form also without enrichment, with the opacity being a key aspect in the growth history and favorable formation location. Finally, we show that the formation of Neptune-like planets remains a challenge for planet formation theories.

Comments:    Accepted for publication in ApJ
Subjects:    Earth and Planetary Astrophysics (astro-ph.EP)
Cite as:    arXiv:1709.04736 [astro-ph.EP]  (or arXiv:1709.04736v1 [astro-ph.EP] for this version)
Submission history
From: Julia Venturini
[v1] Thu, 14 Sep 2017 12:42:29 GMT (2766kb,D)
https://arxiv.org/abs/1709.04736