The diverse chemistry of protoplanetary disks as revealed by JWST

Abstract

Early results from the James Webb Space Telescope-Mid-InfraRed Instrument (JWST-MIRI) guaranteed time programs on protostars (JOYS) and disks (MINDS) are presented. Thanks to the increased sensitivity, spectral and spatial resolution of the MIRI spectrometer, the chemical inventory of the planet-forming zones in disks can be investigated with unprecedented detail across stellar mass range and age. Here, data are presented for five disks, four around low-mass stars and one around a very young high-mass star. The mid-infrared spectra show some similarities but also significant diversity: some sources are rich in CO₂, others in H₂O or C₂H₂. In one disk around a very low-mass star, booming C₂H₂ emission provides evidence for a “soot” line at which carbon grains are eroded and sublimated, leading to a rich hydrocarbon chemistry in which even di-acetylene (C₄H₂) and benzene (C₆H₆) are detected. Together the data point to an active inner disk gas-phase chemistry that is closely linked to the physical structure (temperature, snowlines, presence of cavities and dust traps) of the entire disk and which may result in varying CO₂/H₂O abundances and high C/O ratios >1 in some cases. Ultimately, this diversity in disk chemistry will also be reflected in the diversity of the chemical composition of exoplanets.