A rich hydrocarbon chemistry and high C to O ratio in the inner disk around a very low-mass star

• Published in: Nature astronomy Vol. 7; no. 7; pp. 805 - 814
• Main Authors: Tabone, B., Bettoni, G., van Dishoeck, E. F., Arabhavi, A. M., Grant, S., Gasman, D., Henning, Th, Kamp, I., Güdel, M., Lagage, P. O., Ray, T., Vandenbussche, B., Abergel, A., Absil, O., Argyriou, I., Barrado, D., Boccaletti, A., Bouwman, J., Caratti o Garatti, A., Geers, V., Glauser, A. M., Justannont, K., Lahuis, F., Mueller, M., Nehmé, C., Olofsson, G., Pantin, E., Scheithauer, S., Waelkens, C., Waters, L. B. F. M., Black, J. H., Christiaens, V., Guadarrama, R., Morales-Calderón, M., Jang, H., Kanwar, J., Pawellek, N., Perotti, G., Perrin, A., Rodgers-Lee, D., Samland, M., Schreiber, J., Schwarz, K., Colina, L., Östlin, G., Wright, G.
• Format: Journal Article Web Resource
• Language: English
• Published: London Nature Publishing Group UK 01.07.2023; Nature Publishing Group; Springer Nature
• Subjects: 639/33/34; 639/33/445; and Stellar Astrophysics; Astronomy; Astrophysics - Earth and Planetary Astrophysics; Astrophysics - Solar; Astrophysics and Cosmology; Aérospatiale, astronomie & astrophysique; Benzene; Carbon dioxide; Hydrocarbons; Physical, chemical, mathematical & earth Sciences; Physics; Physics and Astronomy; Physique, chimie, mathématiques & sciences de la terre; Planets; Polycyclic aromatic hydrocarbons; Sciences of the Universe; Space science, astronomy & astrophysics; Space telescopes; Stars; Astrophysics - Earth and Planetary Astrophysics; Astrophysics - Solar and Stellar Astrophysics
• ISSN: 2397-3366; 2397-3366
• DOI: 10.1038/s41550-023-01965-3

Carbon is an essential element for life but how much can be delivered to young planets is still an open question. The chemical characterization of planet-forming disks is a crucial step in our understanding of the diversity and habitability of exoplanets. Very low-mass stars (less than 0.2  M ⊙ ) are interesting targets because they host a rich population of terrestrial planets. Here we present the James Webb Space Telescope detection of abundant hydrocarbons in the disk of a very low-mass star obtained as part of the Mid-InfraRed Instrument mid-INfrared Disk Survey (MINDS). In addition to very strong and broad emission from C 2 H 2 and its 13 C 12 CH 2 isotopologue, C 4 H 2 , benzene and possibly CH 4 are identified, but water, polycyclic aromatic hydrocarbons and silicate features are weak or absent. The lack of small silicate grains indicates that we can look deep down into this disk. These detections testify to an active warm hydrocarbon chemistry with a high C/O ratio larger than unity in the inner 0.1 astronomical units (AU) of this disk, perhaps due to destruction of carbonaceous grains. The exceptionally high C 2 H 2 /CO 2 and C 2 H 2 /H 2 O column density ratios indicate that oxygen is locked up in icy pebbles and planetesimals outside the water iceline. This, in turn, will have important consequences for the composition of forming exoplanets. Highly abundant hydrocarbons in a very low-mass star’s disk are detected using the JWST. This unique chemical composition is probably due to the destruction of carbon grains, and the resulting high gaseous C/O ratio may have a profound impact on the composition of growing exoplanets.