On the formation of planetary systems in photoevaporating transition discs

TL;DR

This study investigates how planetary cores evolve and migrate in photoevaporating transition discs, revealing that such environments can produce systems similar to our solar system or habitable zone planets, depending on disc mass.

Contribution

It provides new insights into planet formation and migration in photoevaporating discs, highlighting the impact of disc mass and gap formation on planetary system architecture.

Findings

Small cores form non-resonant systems beyond 0.5 au.

More massive cores form systems of a few Earth masses.

Low flux transition discs may host Earth-mass planets in habitable zones.

Abstract

In protoplanetary discs, planetary cores must be at least 0.1 earth mass at 1 au for migration to be significant; this mass rises to 1 earth mass at 5 au. Planet formation models indicate that these cores form on million year timescales. We report here a study of the evolution of 0.1 earth mass and 1 earth mass cores, migrating from about 2 and 5 au respectively, in million year old photoevaporating discs. In such a disc, a gap opens up at around 2 au after a few million years. The inner region subsequently accrete onto the star on a smaller timescale. We find that, typically, the smallest cores form systems of non-resonant planets beyond 0.5 au with masses up to about 1.5 earth mass. In low mass discs, the same cores may evolve in situ. More massive cores form systems of a few earth masses planets. They migrate within the inner edge of the disc gap only in the most massive discs. Delivery of material to the inner parts of the disc ceases with opening of the gap. Interestingly, when the heavy cores do not migrate significantly, the type of systems that are produced resembles our solar system. This study suggests that low mm flux transition discs may not form systems of planets on short orbits but may instead harbour earth mass planets in the habitable zone.