James-Webb wrote down the chemical composition of a protoplanetary disk. A remarkable discovery, knowing that the composition of a rocky planet plays a large role in a planet’s habitability. For this reason, it is interesting to follow the evolution of the chemical composition of dust grains during the formation of a planet. Explanation by Benoît Tabone, CNRS researcher at the Institute for Space Astrophysics and author of the study published in the journal Nature Astronomy.
You will also be interested
[EN VIDÉO] The Mystery of the Birth of the Planets The planets are surprisingly diverse and complex. Eight in number in our solar system…
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 star J160532. This “made it possible to reveal the chemical composition of this hydrocarbon-rich disc,” explains Benoît Tabone, CNRS researcher at the Space Astrophysics Institute (Paris Saclay University). A discovery much more interesting than it seems.
These remarkable results are a “first glimpse of the James Webb Space Telescope’s potential to learn more about the physical and chemical conditions prevailing in these dust and gas disks during planet formation.”
Understand the birth of the planets better
In fact, you should know that this is where “the planets are born, in the heart of the dust and gas disks that orbit young stars”. Matter agglomerates there into “protoplanets” that continue to grow by collecting the materials they encounter in the disk. But “knowledge of this process remains limited, so there is interest in studying it”. To this end, scientists from 11 European countries have joined the Minds consortium (Miri mid-INfrared Disk Survey) to study about fifty of these disks with the Miri instrument on board the James Webb telescope. This program aims to “determine the properties of these disks around a variety of stars of different masses and eventually derive statistics.”
Yesterday, Thursday, May 11th, the Minds Consortium published in the journal Nature Astronomy the results of the study of one of those first-ever protoplanetary disks, the one 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, which formed about three million years ago, when compared to the Sun’s age of more than four and a half billion years, and is only 500 light-years from Earth, became “about five to ten times smaller” because of “its low mass.” , chosen as that of the sun”.
“J160532 could help us better understand how these potentially habitable small rocky planets form”
To understand this choice of a star that is very different from the Sun, it is important to note that observations over the last few years “have shown that there are a great many rocky exoplanets in the vicinity of these ‘bright’ stars.” These exoplanets also often form in the “habitable zone of their star, as evidenced by the famous Trappist-1 exoplanet system.” J160532’s protoplanetary disk is therefore likely antecedent to that of Trappist-1, which “could help us better understand how these potentially habitable small rocky planets form.”
Molecules detected in a disk for the first time
With the Miri instrument, James-Webb was able to “reveal the chemical makeup of this hydrocarbon-rich disk.” While astronomers expected to see some of the identified molecules, Miri’s observations still reveal some big surprises. By separating the infrared light emitted by the gas in J160532’s disk, the Miri instrument “allowed the detection of a very large amount of acetylene (C2H2), a simple and very reactive hydrocarbon molecule.” The discovery of previously unknown molecules in protoplanetary disks also caused a surprise: two other hydrocarbons, benzene (C6H6) and diacetylene (C4H2), were actually 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, while these two oxygen-containing molecules are regularly detected in other disks. The authors of this study “propose the hypothesis that the fixed carbon in the J160532 disk would have gasified due to the intense activity of the young star.”
This would mean that the rocky planets formed from the disc’s dust grains should have a “low-carbon mineral composition like Earth”. An interesting discovery, because “the composition of the siliceous mantle plays an important role in the geochemical activity (volcanoes, plate tectonics) of the planet and thus in its habitability”.
To complete these results and improve our knowledge, new observations are planned, again with James-Webb. This time, “we want to observe the disk at shorter wavelengths to detect carbon monoxide, a key compound in disk chemistry.” The Minds Consortium also made a request to the committee that manages the observing times of the Alma Observatory, which operates in the millimeter and submillimeter range. Unlike James-Webb, which “allows access only to a small central portion of the disk,” Alma must allow us “to observe the composition of the outer portion of the disk, which helps us understand the entire disk.”