An international team - including Valentin Christiaens from the University of Liège - used the JWST space telescope to study the protoplanetary disc around ISO-ChaI-147, a young very low-mass star. The results reveal the richest chemical diversity observed to date in a disc, and improve our understanding of the diversity of planetary systems. These results have been published in the journal Science.
P
lanets form in disks of gas and dust - called protoplanetary disks - orbiting young stars. The data we have indicate that terrestrial planets form more efficiently than gas giants in the discs surrounding very low-mass stars, which are the most abundant in our galaxy. Although rocky planets around very low-mass stars are the most common type of planet around the most common stars in our galaxy, their planetary composition remains largely unknown. This is the case, for example, of the seven rocky planets in the TRAPPIST-1 system, whose composition has generally been considered to be Earth-like.
New data provided by the JWST suggests that the composition of protoplanetary disks around very low-mass stars may evolve differently from that of disks around more massive stars such as our Sun. At least, this is what the MIRI Mid-INfrared Disk Survey (MINDS) research programme, which aims to establish a link between the chemical inventory of disks and the properties of exoplanets, has just discovered. In the study that has just been published, the research team explored the region around ISO-ChaI-147, a very low-mass star (0.11 solar masses) in the same category as TRAPPIST-1 , but much younger and still surrounded by a protoplanetary disc. These observations provide a better understanding of the environment and the building blocks used to form these planets. The team was able to observe that the gas in the disc is rich in carbon. This can be explained by the efficient extraction of carbon from solid material, potentially via the sublimation of hydrocarbons on the surface of dust grains when these migrate towards their star - where it is warmer. This reduction in the amount of carbon in solid matter would mean that the rocky planets forming in these discs would be low in carbon. The Earth is also considered to be relatively carbon-poor, but MINDS observations of discs around Sun-like stars show that the gas in these discs is much richer in oxygen species (such as CO2 or H2O) than in the case of ISO-ChaI-147.
This is a major discovery," explains Valentin Christiaens, an astrophysicist at ULiège, "made possible by the high sensitivity of the JWST telescope's mid-infrared instrument (MIRI) and the unprecedented spectral resolution of its spectrometer (MRS). We are talking here about the discovery of the largest variety of hydrocarbons to date: 13 different carbonaceous molecules, within a single protoplanetary disc, and which includes, among other things, the first detection of ethane (C2H6), ethylene (C2H4), propyne (C3H4) or the methyl radical (CH3) in a protoplanetary disc." The PSILab researcher contributed to the development of the pipeline (or processing chain) used to reduce the data and obtain a high-quality spectrum enabling these species to be identified.
Previously, we could only identify acetylene (C2H2) emissions from this object," explains Aditya Arabhavi, researcher at the University of Groningen and first author of the study. However, the greater sensitivity and better spectral resolution of JWST enabled us to detect weak emissions from less abundant molecules. JWST has also enabled us to understand that these hydrocarbon molecules are not only diverse, but also abundant".
The scientific team then intends to extend its study to a larger sample of disks of this type around very low-mass stars, in order to better understand the propensity of these terrestrial-planet forming regions to enrich in carbonaceous gas, and the chemical processes involved to form these molecules. Several features of the JWST data have not yet been identified, so further spectroscopy is needed to fully interpret the observations.
Arabhavi A. & al., Abundant hydrocarbons in the disk around a very-low-mass star, Science, 6 June 2024
https://www.science.org/doi/10.1126/science.adi8147
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Ce Prix, d’un montant de 1.500 euros, récompensera un·e chercheur·euse dont l'ancienneté doctorale est inférieure à 3 ans au 1er janvier 2025, qui se sera distingué·e par la publication d’un mémoire original (master ou doctorat) réalisé à l’ULiège.
