2023-05-12 10:03:07
James-Webb noted the chemical composition of a protoplanetary disc. A remarkable discovery when you know that the composition of a rocky planet plays a big role in the habitability of a planet. This is why it is interesting to follow the evolution of the chemical composition of dust grains during the assembly of a planet. Explanations by Benoît Tabone, CNRS researcher at the Institute for Space Astrophysics and author of the study published in the journal Nature Astronomy.
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The James-Webb Space Telescope, which we knew would make exciting and important discoveries in the field of exoplanets, recently observed the protoplanetary disk of the star J160532. He has ” allowed to reveal the chemical composition of this disc, rich in hydrocarbons », explains Benoît Tabone, CNRS researcher at theInstitute of Space Astrophysics (University-Paris Saclay). A discovery much more interesting than it seems.
These remarkable results are a “ first glimpse of the potential of the James-Webb Space Telescope to learn about the physical and chemical conditions that prevail in these discs of dust and gas during the formation of planets ».
Better understand the birth of the planets
Indeed, it should be known that it is here that ” the planets are born, in the heart of the discs of dust and gas which orbit around the young stars “. The matter agglomerates there to form “protoplanets” which continue their growth by collecting the materials which they encounter in the disc. But the ” knowledge about this process remains limited, hence the interest in studying it “. For this, scientists from 11 European countries have come together in the Minds consortium (Miri mid-INfrared Disk Survey) to study about fifty of these discs, using the Miri instrument on board the James-Webb telescope. This program aims to determine the properties of these discs around a wide variety of stars of different masses and eventually derive statistics ».
Yesterday, Thursday May 11, the Minds consortium published in the journal Nature Astronomy the results of the study of one of these very first protoplanetary disks, that around the star J160532. This star certainly means nothing to you. Neither do we. However, ” it was obviously not chosen at random “. This very young star, formed about three million years ago, against more than four and a half billion years for the Sun for comparison, and located only 500 light years from Earth was chosen because of ” its low mass, about five to ten times lower than that of the Sun ».
“J160532 may help us better understand how these potentially habitable small rocky planets form”
To understand this choice of a star very different from the Sun, it is necessary to know that the observations of these last years have shown that rocky exoplanets are very abundant around these “light” stars “. These exoplanets also often form in the ” habitable zone of their star as evidenced by the famous Trappist-1 exoplanet system “. The protoplanetary disk of J160532 is therefore likely a precursor to that of Trappist-1, which “ may help us better understand how these small, potentially habitable rocky planets form ».
Molecules detected for the first time in a disc
Using the Miri instrument, James-Webb was able to “ reveal the chemical composition of this disc, rich in hydrocarbons “. If astronomers expected to detect some of the molecules identified, Miri’s observations still reveal some major surprises. By dissecting the infrared light emitted by the gas in the disk of J160532, the Miri instrument has ” revealed a very large amount of acetylene (C2H2), a simple and highly reactive hydrocarbon molecule “. The discovery of molecules hitherto unknown in protoplanetary disks also came as a surprise: two other hydrocarbons, benzene (C6H6) and diacetylene (C4H2) have indeed been identified ».
Thus, disk J160532 seems extremely rich in carbon molecules in the form of gas, with very little water and carbon dioxide, whereas these two molecules containing oxygen are regularly detected in other disks. The authors of this study argue that the hypothesis that the solid carbon in the J160532 disc has changed to a gaseous state due to the intense activity of the young star ».
This would imply that rocky planets formed from disk dust grains should have a ” mineral composition low in carbon just like the Earth “. An interesting discovery since the composition of the earth’s mantle, rich in silicate, plays a major role in the geochemical activity (volcanoes, plate tectonics) of the planet and therefore in its habitability ».
To complete these results and improve our knowledge, new observations are planned, again with James-Webb. This time, ” we wish to observe the disc in shorter wavelengths in order to detect carbon monoxide, a key compound for the chemistry of the discs “. The Minds consortium also made a request to the committee that manages the observation times of the Alma observatory, which operates in the millimeter and submillimeter range. Unlike the James-Webb, which ” gives access to only a small central part of the disk “Alma must allow us” to observe the composition of the outer part of the disk, which will help us in understanding the whole disk ».
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