Evidence of Different Formation Mechanisms for Hot versus Warm Super-Earths

TL;DR

This study reveals that hot and warm super-Earths likely form through different mechanisms, as evidenced by their distinct relationships with host star metallicity and a transition period around 70-100 days.

Contribution

It provides observational evidence for at least two different formation mechanisms for super-Earths based on their orbital periods and host star metallicity dependence.

Findings

Shorter-period super-Earths are more metal-rich than longer-period ones.

A transition period between 70 and 100 days marks a change in formation characteristics.

Super-Earths likely form via multiple mechanisms, not a single process.

Abstract

Using the Kepler planet sample from Buchhave et al. and the statistical method clarified by Schlaufman, I show that the shorter-period super-Earths have a different dependence on the host star metallicity from the longer-period super-Earths, with the transition period being in the period range from 70 to 100 days. The hosts of shorter-period super-Earths are on average more metal-rich than those of longer-period super-Earths. The existence of such a transition period cannot be explained by any single theory of super-Earth formation, suggesting that super-Earths have formed via at least two mechanisms.