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Exploring plausible formation scenarios for the planet candidate orbiting Proxima Centauri

Status Report From: arXiv.org e-Print archive
Posted: Wednesday, August 24, 2016

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Gavin A. L. Coleman, Richard P. Nelson, Sijme-Jan Paardekooper, Stefan Dreizler, Benjamin Giesers, Guillem Anglada-Escude
(Submitted on 24 Aug 2016)

We present a study of 4 different formation scenarios that may explain the origin of the recently announced planet `Proxima b' orbiting the star Proxima Centauri. The aim is to examine how the formation scenarios differ in their predictions for the multiplicity of the Proxima planetary system, the water/volatile content of Proxima b and its eccentricity, so that these can be tested by future observations.

A scenario of in situ formation via giant impacts from a locally enhanced disc of planetary embryos and planetesimals, predicts that Proxima b will be a member of a multiplanet system with a measurably finite value of orbital eccentricity. Assuming that the local solid enhancement needed to form a Proxima b analogue with a minimum mass of 1.3 Earth masses arises because of the inwards drift of solids in the form of small planetesimals/boulders, this scenario also likely results in Proxima b analogues that are moderately endowed with water/volatiles, arising from the dynamical diffusion of icy planetesimals from beyond the snowline during planetary assembly.

A scenario in which multiple embryos form, migrate and mutually collide within a gaseous protoplanetary disc also results in Proxima b being a member of a multiple system, but where its members are Ocean planets due to accretion occurring mainly outside of the snowline, possibly within mean motion resonances. A scenario in which a single accreting embryo forms at large distance from the star, and migrates inwards while accreting either planetesimals/pebbles results in Proxima b being an isolated Ocean planet on a circular orbit. A scenario in which Proxima b formed via pebble accretion interior to the snowline produces a dry planet on a circular orbit. Future observations that characterise the physical/orbital properties of Proxima b, and the multiplicity of the system, will provide valuable insight into its formation history.

Comments: 10 pages, 9 Figures. Submitted to MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1608.06908 [astro-ph.EP] (or arXiv:1608.06908v1 [astro-ph.EP] for this version)
Submission history
From: Gavin Coleman
[v1] Wed, 24 Aug 2016 17:58:33 GMT (342kb,D)
http://arxiv.org/abs/1608.06908

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