The dynamical evolution of transiting planetary systems including a realistic collision prescription

TL;DR

This study investigates how realistic collision models, including debris removal, influence the evolution and final architecture of transiting planetary systems, highlighting differences from perfect-merging assumptions especially during formation.

Contribution

It introduces a realistic collision prescription into N-body simulations, showing its impact on planetary embryo growth and the Kepler Dichotomy.

Findings

Fewer detectable planets form with realistic collisions when debris is rapidly removed.

The effect on mature super-Earth systems is minimal due to grazing impacts.

Perfect merging assumptions overestimate planetary growth and system multiplicity.

Abstract

Planet-planet collisions are a common outcome of instability in systems of transiting planets close to the star, as well as occurring during in-situ formation of such planets from embryos. Previous N-body studies of instability amongst transiting planets have assumed that collisions result in perfect merging. Here, we explore the effects of implementing a more realistic collision prescription on the outcomes of instability and in-situ formation at orbital radii of a few tenths of an au. There is a strong effect on the outcome of the growth of planetary embryos, so long as the debris thrown off in collisions is rapidly removed from the system (which happens by collisional processing to dust, and then removal by radiation forces) and embryos are small ($< 0.1\mathrm{\,M}_\oplus$). If this is the case, then systems form fewer detectable ($\gtrsim1\mathrm{\,M}_\oplus$) planets than systems evolved under the assumption of perfect merging in collisions. This provides some contribution to the "Kepler Dichotomy": the observed over-abundance of single-planet systems. The effects of changing the collision prescription on unstable mature systems of super-Earths are less pronounced. Perfect mergers only account for a minority of collision outcomes in such systems, but most collisions resulting in mass loss are grazing impacts in which only a few per cent. of mass is lost. As a result, there is little impact on the final masses and multiplicities of the systems after instability when compared to systems evolved under the assumption that collisions always result in perfect merging.