Formation of Rocky Super-Earths From A Narrow Ring of Planetesimals

TL;DR

This paper presents a theoretical model for the formation of rocky super-Earths from a narrow ring of planetesimals at about 1 AU, explaining their properties and diversity through collisions, isolation, and migration, supported by numerical simulations.

Contribution

It introduces a new formation scenario for super-Earths originating from a narrow ring of planetesimals, supported by numerical simulations that replicate observed planetary system features.

Findings

Synthetic systems resemble observed short-period super-Earths.

Planet growth is driven by pairwise collisions and regulated by isolation and migration.

Absence of short-period super-Earths in the solar system explained by low initial planetesimal mass.

Abstract

The formation of super-Earths, the most abundant planets in the Galaxy, remains elusive. These planets have masses that typically exceed that of the Earth by a factor of a few; appear to be predominantly rocky, although often surrounded by H/He atmospheres; and frequently occur in multiples. Moreover, planets that encircle the same star tend to have similar masses and radii, whereas those belonging to different systems exhibit remarkable overall diversity. Here, we advance a theoretical picture for rocky planet formation that satisfies the aforementioned constraints: building upon recent work - which demonstrates that planetesimals can form rapidly at discrete locations in the disk - we propose that super-Earths originate inside rings of silicate-rich planetesimals at approximately ~1 AU. Within the context of this picture, we show that planets grow primarily through pairwise collisions among rocky planetesimals, until they achieve terminal masses that are regulated by isolation and orbital migration. We quantify our model with numerical simulations and demonstrate that our synthetic planetary systems bear a close resemblance to compact, multi-resonant progenitors of the observed population of short-period extrasolar planets. Our results thus indicate that the absence of short-period super-Earths within the solar system can simply be attributed to the comparatively low mass of the primordial planetesimal ring within the protosolar nebula.