Very-low-mass stars host orbiting rocky exoplanets more frequently than other types of stars. The compositions of those planets are largely unknown but are expected to relate to the protoplanetary disk in which they form. In new research, astronomers used the NASA/ESA/CSA James Webb Space Telescope to investigate the chemical composition of the planet-forming disk around ISO-ChaI 147, a red dwarf star weighing just one-tenth as much as our Sun. They identified emission from 13 carbon-bearing molecules, including ethane and benzene.
This is an artist’s impression of a young star surrounded by a disk of gas and dust. Image credit: NASA / JPL.
ISO-ChaI 147 is a 0.11-solar-mass red dwarf located approximately 639 light-years away in the constellation of Chamaeleon.
This star was observed as part of the MIRI Mid-INfrared Disk Survey (MINDS), which aims to build a bridge between the chemical inventory of disks and the properties of exoplanets.
These observations provide insights into the environment as well as basic ingredients for such planets to form.
The astronomers found that the gas in the planet-forming region of ISO-ChaI 147 is rich in carbon.
This could potentially be because carbon is removed from the solid material from which rocky planets can form, and could explain why Earth is relatively carbon-poor.
“Webb has a better sensitivity and spectral resolution than previous infrared space telescopes,” said Dr. Aditya Arabhavi, an astronomer at the University of Groningen.
“These observations are not possible from Earth, because the emissions are blocked by the atmosphere.”
“Previously we could only identify acetylene emission from this object.”
“However, Webb’s higher sensitivity and spectral resolution allowed us to detect weak emission from less abundant molecules.”
“Webb also allowed us to understand that these hydrocarbon molecules are not just diverse but also abundant.”
The spectrum of ISO-ChaI 147 shows the richest hydrocarbon chemistry seen to date in a protoplanetary disk, consisting of 13 carbon-bearing molecules. Image credit: NASA / ESA / CSA / Ralf Crawford, STScI.
The spectrum of ISO-ChaI 147 revealed by Webb’s Mid-InfraRed Instrument (MIRI) shows the richest hydrocarbon chemistry seen to date in a protoplanetary disk, consisting of 13 carbon-bearing molecules up to benzene.
This includes the first extrasolar detection of ethane, the largest fully-saturated hydrocarbon detected outside our Solar System.
Since fully-saturated hydrocarbons are expected to form from more basic molecules, detecting them here gives researchers clues about the chemical environment.
The astronomers also detected ethylene, propyne, and the methyl radical, for the first time in a protoplanetary disk.
“These molecules have already been detected in our Solar System, for example in comets such as 67P/Churyumov-Gerasimenko and C/2014 Q2 (Lovejoy),” Dr. Arabhavi said.
“It is amazing that we can now see the dance of these molecules in the planetary cradles.”
“It is a very different planet-forming environment from what we usually think of.”
The team indicates that these results have large implications for astrochemistry in the inner 0.1 AU and the planets forming there.
“This is profoundly different from the composition we see in disks around solar-type stars, where oxygen bearing molecules dominate (like carbon dioxide and water),” said Dr. Inga Kamp, also from the University of Groningen.
“This object establishes that these are a unique class of objects.”
“It’s incredible that we can detect and quantify the amount of molecules that we know well on Earth, such as benzene, in an object that is more than 600 light-years away,” said Dr. Agnés Perrin, an astronomer at the Centre National de la Recherche Scientifique.
The team’s results appear today in the journal Science.
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A.M. Arabhavi et al. 2024. Abundant hydrocarbons in the disk around a very-low-mass star. Science 384, 6700: 1086-1090; doi: 10.1126/science.adi8147
