Planet-Planet Scattering Alone Cannot Explain the Free-Floating Planet Population

TL;DR

This paper argues that planet-planet scattering alone cannot account for the large population of free-floating planets observed, suggesting other mechanisms like stellar cluster stripping and post-main-sequence ejection are also significant.

Contribution

The study provides quantitative analysis and simulations showing the insufficiency of scattering alone to explain free-floating planet numbers, highlighting the need for alternative sources.

Findings

Scattering cannot produce enough free-floating planets to match observations.

Other mechanisms like stellar cluster stripping are likely important.

Quantitative and simulation methods support the conclusions.

Abstract

Recent gravitational microlensing observations predict a vast population of free-floating giant planets that outnumbers main sequence stars almost twofold. A frequently-invoked mechanism for generating this population is a dynamical instability that incites planet-planet scattering and the ejection of one or more planets in isolated main sequence planetary systems. Here, we demonstrate that this process alone probably cannot represent the sole source of these galactic wanderers. By using straightforward quantitative arguments and N-body simulations, we argue that the observed number of exoplanets exceeds the plausible number of ejected planets per system from scattering. Thus, other potential sources of free-floaters, such as planetary stripping in stellar clusters and post-main-sequence ejection, must be considered.