First detection of benzene in a planet-forming disk

2023-05-11 17:18:17

MADRID, 11 May. (EUROPA PRESS) –

Observations with the Webb Space Telescope have revealed, for the first time, the benzene (C6H6) molecule in a planet-forming disk around a young star.

In addition to benzene, an international team of astronomers detected many other smaller carbon compounds and few oxygen-rich molecules. The observations suggest that, like our own Earth, the rocky planets that form in this disk contain relatively little carbon. The scientists published their findings in the journal Nature Astronomy.

The researchers studied the young and small star J160532 (one tenth of the mass of our sun). about 500 light years of us in the constellation of Scorpio. Around such small and young stars, many rocky, Earth-like planets form in disks made of gas and dust. Until now, it has been difficult to study molecules in the warm inner part of these disks where most planets form. due to the limited sensitivity and spectral resolution of previous observatories.

For their research, the scientists used data from Webb’s MIRI spectrometer, which can see through dust clouds and is particularly suitable for measuring hot gas in internal disks. The main optics of the MIRI spectrometer were designed and built by the Netherlands Research School of Astronomy (NOVA), who participated in the study.

“This is exactly the kind of science the MIRI spectrometer was designed for,” says Ewine van Dishoeck (Leiden University), who has been involved in building Webb and the MIRI instrument from the very beginning. “The spectra contain a wealth of data that tells us something about the chemical and physical composition of planet-forming disks.”

VERY LITTLE WATER AND CO2

In addition to the first observation of benzene in a planet-forming disk, the researchers also observed for the first time the hydrocarbon diacetylene (C4H2) and an unusually large amount of acetylene gas (C2H2), a highly reactive hydrocarbon. Surprisingly, there is very little water and carbon dioxide in this disk. However, those oxygen-rich compounds are often found in other dusty disks. Identification of these molecules required close collaboration with the chemists who measure the spectra (the chemical fingerprints) in the laboratory..

The researchers suspect that benzene and (di-)acetylene are released into the disk after the destruction of carbon-rich dust grains by the young active star. The remaining dust grains would contain relatively low carbon silicates. In a later phase, the low carbon beans are grouped into larger pieces. These eventually become rocky planets like Earth. This scenario may explain why our own Earth is so carbon poor.

Meanwhile, the researchers are working on data from more than 30 other dust disks around young stars, and data from 20 more disks are expected this year. In doing so, it is hoped that they will discover other molecules and gain more knowledge about the formation of planets around stars, from the smallest to those with 2 to 3 times the mass of our sun.

Lead study author Benoît Tabone (now a CNRS researcher at Université Paris-Saclay in France and formerly affiliated with Leiden University) says: “This work is just a first glimpse of the physical and chemical conditions under which Earth-like planets, like our Earth, formed.”