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

Modeling observations of the archetypal debris disk around beta 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 mu m continuum excess modeled using a similar to 600 K black body has disappeared. The previously prominent 18 and 23 mu m crystalline forsterite emission features, arising from cold dust (similar to 100 K) in the Rayleigh limit, have disappeared and been replaced by very weak features arising from the hotter 500 K dust population.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 mu m silicate feature has changed, consistent with a shift in the temperature of the warm dust population from similar to 300 to similar 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 beta 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.