A Disintegrating Rocky World Shrouded in Dust and Gas: Mid-IR Observations of K2-22b using JWST

TL;DR

This study uses JWST's MIRI instrument to observe the disintegrating exoplanet K2-22b, revealing spectral features that suggest a rocky interior with possible gaseous components, advancing understanding of such chaotic planetary systems.

Contribution

First mid-infrared transmission spectra of K2-22b obtained with JWST, providing new insights into its interior composition and gaseous environment.

Findings

Data disfavor iron-dominated core material

Spectral consistency with magnesium silicate minerals

Detection of an unexpected $ extasciitilde$5 μm feature possibly from gaseous NO or CO₂

Abstract

The disintegrating ultra-short period rocky exoplanet K2-22b periodically emits dusty clouds in a dynamically chaotic process resulting in a variable transit depth from 0-1.3%. The effluents that sublimate off the surface and condense out in space are probably representative of the formerly interior layers convectively transported to the molten surface. Transmission spectroscopy of these transiting clouds reveal spectral fingerprints of the interior composition of this rocky world. We used JWST's Mid-Infrared Instrument (MIRI) as a low-resolution slitless spectrograph to observe four predicted transit windows for K2-22b. For each observation, we extracted a transmission spectrum over the spectral range of 4.4-11.8 $\mu$m. Over the spectral range of 4.4-8 $\mu$m, where the spectral precision is highest, we detect one transit at high significance and two at low significance. While the S/N of the spectrum limits our ability to draw firm conclusions, we find that the data: 1) disfavor featureless, iron-dominated core material, 2) are consistent with some form of magnesium silicate minerals, likely from mantle material, and 3) show a distinct and unexpected feature at $\sim$5 $\mu$m. The unexpected feature, also seen weakly in the low-significance transits, is consistent with an unknown gaseous absorber, possibly NO and/or CO$_2$. These findings warrant further study to improve the constraints on the composition of this disintegrating rocky world.