Seismic Oscillations Excited by Giant Impacts in Directly-Imaged Giant Planets

TL;DR

This paper proposes that giant impacts on young gas giants can excite long-lasting seismic oscillations detectable through photometric variability, providing insights into their interior composition and impact history.

Contribution

It introduces the concept that giant impacts induce seismic oscillations in young gas giants, which can be observed photometrically and used to study their internal structure.

Findings

Seismic oscillations have periods of tens of minutes to an hour.

Mode lifetimes are comparable to the planet's Kelvin-Helmholtz time.

Photometric variability exceeding 1% can last for millions of years.

Abstract

The radii and masses of many giant exoplanets imply their interiors each contain more than $\sim$100 $M_\oplus$ of solids. A large metal content may arise when a giant planet grows by colliding and merging with multiple $\sim$10 $M_\oplus$ solid cores. Here we show that a giant impact with a young gas giant excites long-lived seismic oscillations that can be detected photometrically. Mode lifetimes are close to the planet's Kelvin-Helmholtz time, a significant fraction of a young planet's age. Oscillation periods lie between tens of minutes to an hour, and variability amplitudes can exceed a percent for several million years. Beta Pictoris b is a young super-Jupiter known to be highly metal-enriched. If a Neptune-mass (17 $M_\oplus$) body impacted $\beta$ Pictoris b in the past $\sim$9--18 Myr, the planet could still be ringing with a percent-level photometric variability measurable with JWST.