MIRI MRS Observations of Beta Pictoris. II. The Spectroscopic Case for a Recent Giant Collision

Abstract

Modeling observations of the archetypal debris disk around β Pic, obtained in 2023 January with the MIRI Medium Resolution Spectrograph on board JWST, reveals significant differences compared with that obtained with the Infrared Spectrograph on board Spitzer. The bright 5–15 μm continuum excess modeled using a ∼600 K black body has disappeared. The previously prominent 18 and 23 μm crystalline forsterite emission features, arising from cold dust (∼100 K) in the Rayleigh limit, have disappeared and been replaced by very weak features arising from the hotter 500 K dust population. Finally, the shape of the 10 μm silicate feature has changed, consistent with a shift in the temperature of the warm dust population from ∼300 to ∼500 K and an increase in the crystalline fraction of the warm, silicate dust. Stellar radiation pressure may have blown both the hot and the cold crystalline dust particles observed in the Spitzer spectra out of the planetary system during the intervening 20 yr between the Spitzer and JWST observations. These results indicate that the β Pic system has a dynamic circumstellar environment, and that periods of enhanced collisions can create large clouds of dust that sweep through the planetary system.