Origin of compact exoplanetary systems during disk infall

TL;DR

This paper proposes that compact exoplanetary systems are remnants of planet formation during ongoing disk infall, with their masses regulated by a balance between accretion and migration, explaining their similar mass ratios.

Contribution

It introduces a new model where planet formation occurs during disk infall, accounting for the observed properties of compact exoplanetary systems.

Findings

Infall-produced planets can survive until disk dispersal.

Planet masses are regulated by infall and disk conditions.

Explains the similar mass ratios in observed systems.

Abstract

Exoplanetary systems that contain multiple planets on short-period orbits appear to be prevalent in the current observed exoplanetary population, yet the processes that give rise to such configurations remain poorly understood. A common prior assumption is that planetary accretion commences after the infall of gas and solids to the circumstellar disk ended. However, observational evidence indicates that accretion may begin earlier. We propose that compact systems are surviving remnants of planet accretion that occurred during the final phases of infall. In regions of the disk experiencing ongoing infall, the planetary mass is set by the balance between accretion of infalling solids and the increasingly rapid inward migration driven by the surrounding gas as the planet grows. This balance selects for similarly-sized planets whose mass is a function of infall and disk conditions. We show that infall-produced planets can survive until the gas disk disperses and migration ends, and that across a broad range of conditions, the mass of surviving systems is regulated to a few 10^{-5} to 10^{-4} times the host star's mass. This provides an explanation for the similar mass ratios of known compact systems.