The James Webb Telescope reveals the composition of a protoplanetary disk

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The MIRI spectrum of the star J160532. The emission lines of benzene (C6H6), dia
The MIRI spectrum of the star J160532. The emission lines of benzene (C6H6), diacetylene (C4H2) and carbon dioxide (CO2) appear as narrow peaks in the spectrum. Acetylene is so abundant that it produces two broad bumps in the spectrum. This indicates the predominance of hydrocarbons in the disk. The emission of water, commonly observed in other disks, is weak or absent. Benoît Tabone/MINDS consortium/NASA/ESA
  • Young stars are surrounded by disks of material where future planets are born.

  • The James Webb telescope has revealed the chemical composition of the disk of the star J160532, rich in hydrocarbons.

  • Observations in recent years have shown that rocky exoplanets are very abundant around "light" stars like J160532.

An international research team involving scientists from CNRS, Université Paris-Saclay and CEA, supported by CNES, has just revealed the chemical composition of a disk of matter rotating around a young star, where new planets are forming. Surprisingly, this disk is rich in hydrocarbons, two molecules of this family having even been detected for the first time in a disk. These results, published on May 11 in the journal Nature Astronomy, were obtained with the MIRI instrument developed by a consortium of laboratories in Europe 1 and the United States.

1 Under the project management of CEA and the project management of CNES, several French laboratories played a key role in providing the MIRI imager: The Astrophysics, Instrumentation, Modeling Laboratory (CEA/CNRS/Université Paris Cité), the Space Astrophysics Institute (CNRS/Université Paris-Saclay), the Laboratory for Space Studies and Instrumentation in Astrophysics (Observatoire de Paris-PSL/CNRS/Sorbonne Université/Université Paris Cité), the Marseille Astrophysics Laboratory (CNRS/Aix Marseille Université).

This is where planets are born, in the heart of the dust and gas disks that form around a young star after its birth. Matter clumps together to form "protoplanets" that continue to grow by collecting material they encounter in the disk. But the knowledge on this process remains limited.

Among the mysteries that still surround protoplanetary disks, scientists from 11 European countries 1 gathered in the MINDS(MIRI mid- Infrared Disk Survey) consortium have just partially lifted the veil on their chemical composition. Observations of the very young star J160532 2 and its disk, carried out with the James Webb Space Telescope, have revealed surprisingly abundant hydrocarbons. Some are even detected for the first time in a disk.

The research team relied for that on the MIRI spectrometer of the telescope. By dissecting the infrared light emitted by the gas in the disk of J160532, the instrument revealed a very large amount of acetylene (C2H2), a simple and highly reactive hydrocarbon molecule. The discovery of previously unknown molecules in protoplanetary disks also created a surprise: two other hydrocarbons, benzene (C6H6) and diacetylene (C4H#x2) have indeed been identified.

Thus, the J160532 disk appears to be extremely rich in carbon molecules in the form of gas, with very little water and carbon dioxide, whereas these two oxygen-containing molecules are regularly detected in other disks. The authors of this study propose the hypothesis that the solid carbon in the disk J160532 would have passed to the gas state because of the intense activity of the young star. This would imply that the rocky planets formed from the dust grains of the disk should have a mineral composition poor in carbon, just like the Earth. On the contrary, the gaseous planets should be rich in carbon.

The consortium had chosen to focus on J160532 because of its low mass, about five to ten times lower than that of the Sun. Indeed, the observations of these last years have shown that rocky exoplanets are very abundant around these "light" stars. These exoplanets often form in the habitable zone of their star as shown by the famous Trappist-1 exoplanet system.

These results are a first glimpse of the potential of the James Webb Space Telescope to learn about the physical and chemical conditions that prevail during planet formation. Scientists now want to study the full diversity of protoplanetary disks to understand how the same physical processes that operate in all disks lead to the different types of planets observed in the Universe, including those in our Solar System.

1 In France, this research involved scientists from the Institute of Space Astrophysics (CNRS/University of Paris-Saclay), the Astrophysics, Instrumentation, Modeling Laboratory (CNRS/CEA/Université Paris Cité), the Laboratory ofétudes du rayonnement et de la matière en astrophysique et atmosphères (Observatoire de Paris - PSL/CNRS/Sorbonne Université/Université de Cergy-Pontoise) and the Laboratoire de météorologie dynamique (CNRS/ENS-PSL/École polytechnique/Sorbonne Université), as well as financial support from CNES.

2 J160532 was formed about three million years ago, against more than four billion for the Sun as a comparison.


A rich hydrocarbon chemistry and high C to O ratio in the inner disk around a very low-mass star. Tabone et al. Nature Astronomy, May 11, 2023. DOI:10.1038/s41550’023 -01965-3

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