JWST Reveals Factors Shaping Planet Composition in Low-Mass Star

James Webb Space Telescope (JWST) observations have revealed abundant hydrocarbons in the protoplanetary disk surrounding a young, very-low-mass star – findings that provide novel insights into the chemical environment from which many terrestrial planets, in particular, are born. Planets form in disks of gas and dust that orbit young stars. Observations show that terrestrial planets form more efficiently than gas giant planets around very-low-mass stars (VLMSs) – those with less than 0.3 solar masses. Although the chemical compositions of the inner disk regions around higher mass stars have been previously studied, very few inner disk regions around VLMSs have been investigated. Using the JWST's mid-infrared spectroscopy instrument, Aditya Arabhavi and colleagues investigated the chemical composition of the planet-forming disk around ISO-ChaI 147, a young 0.11-solar-mass star in the Chameleon I star-forming region. Arabhavi et al. found that the inner disk region surrounding this star has a carbon-rich chemistry featuring 13 carbon-bearing molecules, including ethane and benzine. This abundance in hydrocarbon molecules starkly contrasts the lack of observed oxygen-bearing molecules, suggesting that the region has a carbon to oxygen radio of >1. The authors argue that this high carbon/oxygen ratio indicates radial transport of material within the disk, likely affecting the bulk composition of any planets forming within the disk.