Seismic Oscillations Excited by Giant Impacts in Directly Imaged Giant Planets

Abstract The radii and masses of many giant exoplanets imply their interiors each contain more than ∼100 M ⊕ of solids. A large metal content may arise when a giant planet grows by colliding and merging with multiple ∼10 M ⊕ solid cores. Here we show that a giant impact with a young gas giant excites long-lived seismic oscillations that can be detected photometrically. The mode lifetimes are close to the planet’s Kelvin–Helmholtz time, a significant fraction of a young planet’s age. The oscillation periods lie between tens of minutes to an hour, and the 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 ⊕ ) body impacted β Pictoris b in the past ∼9–18 Myr, the planet could still be ringing with a percent-level photometric variability measurable with JWST.