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

• Main Authors: Tabone, B, Bettoni, G, van Dishoeck, E. F, Arabhavi, A. M, Grant, S. L, Gasman, D, Henning, T, Kamp, I, Güdel, M, Lagage, P. -O, Ray, T. P, Vandenbussche, B, Abergel, A, Absil, O, Argyriou, I, Barrado, D, Boccaletti, A, Bouwman, J, Garatti, A. Caratti o, 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. R, Colina, L, Östlin, G, Wright, G
• Format: Journal Article
• Language: English
• Published: 12-04-2023
• Subjects: Physics - Earth and Planetary Astrophysics; Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.2304.05954

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 ($<0.2~M_{\odot}$) are
interesting targets because they host a rich population of terrestrial planets.
Here we present the JWST detection of abundant hydrocarbons in the disk of a
very low-mass star obtained as part of the MIRI 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, PAH and silicate features are weak or absent. The
lack of small silicate grains implies that we can look deep down into this
disk. These detections testify to an active warm hydrocarbon chemistry with a
high C/O ratio in the inner 0.1 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 suggest that oxygen is locked up in icy
pebbles and planetesimals outside the water iceline. This, in turn, will have
significant consequences for the composition of forming exoplanets.