# Signatures of a planet-planet impacts phase in exoplanetary systems hosting giant planets

## TL;DR

This paper proposes that the eccentric orbits of giant exoplanets result from a phase of planet-planet impacts during system formation, with numerical simulations supporting this impact-driven origin and predicting high-mass planets at certain distances.

## Contribution

It introduces a new impact-based scenario for the origin of giant planet eccentricities, supported by numerical simulations of collisional growth in exoplanetary systems.

## Key findings

- High-eccentricity giants may form in systems with higher initial total mass.
- Observed eccentricity distribution is consistent with planet-planet scattering.
- Mergers produce high-mass giants between 1 and 8 au.

## Abstract

Exoplanetary systems host giant planets on substantially non-circular, close-in orbits. We propose that these eccentricities arise in a phase of giant impacts, analogous to the final stage of Solar System assembly that formed Earth's Moon. In this scenario, the planets scatter each other and collide, with corresponding mass growth as they merge. We numerically integrate an ensemble of systems with varying total planet mass, allowing for collisional growth, to show that (1) the high-eccentricity giants observed today may have formed preferentially in systems of higher initial total planet mass, and (2) the upper bound on the observed giant planet eccentricity distribution is consistent with planet-planet scattering. We predict that mergers will produce a population of high-mass giant planets between 1 and 8 au from their stars.