# Collisions of Terrestrial Worlds: The Occurrence of Extreme Mid-Infrared Excesses around Low-Mass Field Stars

## TL;DR

This study investigates the occurrence of extreme mid-infrared excesses around low-mass field stars, suggesting they originate from dust produced by recent planetary collisions, and explores their age and mass dependencies.

## Contribution

It introduces a large sample of stars with extreme MIR excesses, develops a galactic model to estimate sample completeness, and links the excesses to planetary collision events.

## Key findings

- 584 stars with extreme MIR excesses identified
- Excesses likely caused by dust from recent planetary collisions
- Age and mass trends observed in excess occurrence

## Abstract

We present the results of an investigation into the occurrence and properties (stellar age and mass trends) of low-mass field stars exhibiting extreme mid-infrared (MIR) excesses ($L_\mathrm{IR} / L_\ast \gtrsim 0.01$). Stars for the analysis were initially selected from the Motion Verified Red Stars (MoVeRS) catalog of photometric stars with SDSS, 2MASS, and $WISE$ photometry and significant proper motions. We identify 584 stars exhibiting extreme MIR excesses, selected based on an empirical relationship for main sequence $W1-W3$ colors. For a small subset of the sample, we show, using spectroscopic tracers of stellar age (H$\alpha$ and Li ${\rm{\small I}}$) and luminosity class, that the parent sample is likely comprised of field dwarfs ($\gtrsim$ 1 Gyr). We also develop the Low-mass Kinematics ($LoKi$) galactic model to estimate the completeness of the extreme MIR excess sample. Using Galactic height as a proxy for stellar age, the completeness corrected analysis indicates a distinct age dependence for field stars exhibiting extreme MIR excesses. We also find a trend with stellar mass (using $r-z$ color as a proxy). Our findings are consistent with the detected extreme MIR excesses originating from dust created in a short-lived collisional cascade ($\lesssim$ 100,000 years) during a giant impact between two large planetismals or terrestrial planets. These stars with extreme MIR excesses also provide support for planetary collisions being the dominant mechanism in creating the observed $Kepler$ dichotomy (the need for more than a single mode, typically two, to explain the variety of planetary system architectures $Kepler$ has observed), rather than different formation mechanisms.