JWST-TST High Contrast: Medium-resolution spectroscopy reveals a carbon-rich circumplanetary disk around the young accreting exoplanet Delorme 1AB b

Vol. 704
10. Planets, planetary systems, and small bodies

JWST-TST High Contrast: Medium-resolution spectroscopy reveals a carbon-rich circumplanetary disk around the young accreting exoplanet Delorme 1AB b

Delorme 1 is a binary system composed of two M5.5 stars separated by 12 au, hosting a ~13 Jupiter-mass companion, Delorme 1 AB b, in a circumbinary orbit at 84 au projected separation. The UV/NIR spectrum of Delorme 1 AB b shows numerous hydrogen-recombination lines that typically trace accretion from circumplanetary material, indicative of a gas-rich disk despite the object's relatively old (30-45 Myr) age. The object is thus doubly interesting, challenging formation scenarios of low-mass circumbinary companions at large separations, as well as conventional assumptions about disk dispersal timescales. Based on JWST/MIRI data, Mâlin et al. characterize the object in terms of its effective temperature and radius, and, using a cross-correlation technique that detects CO and H2O, infer constraints on its metallicity and C/O ratio. Furthermore, they report the direct detection of a circumplanetary disk (CPD) around Delorme 1 AB b, from excess emission longward of 10 µm. Most remarkably, the CPD spectrum shows clear signatures of gaseous H2 (tracing outflows), HCN, C2H2, and tentatively 12C13CH2, yielding the first detection of molecular line emission from a CPD. In contrast, no evidence is found for O-bearing molecules, suggesting an elevated C/O gas ratio in the disk. This breakthrough study offers a new perspective on CPD chemical composition and physical conditions, and on how accretion persists in such long-lived (nicknamed “Peter Pan”) disks.