Webb identifies surprising carbon-rich ingredients around young star

by Haygen Warren

Using the joint NASA, European Space Agency (ESA), and Canadian Space Agency (CSA) James Webb Space Telescope, a team of international scientists studied a disk of cosmic material surrounding an extremely low-mass star. The results from the investigation show the richest hydrocarbon chemistry ever observed within a protoplanetary disk, which is a disk of gas, dust, ice, and other material that surrounds a newly formed star wherein planets can form.

The new Webb observations were made as part of the MIRI Mid-Infrared Disk Survey (MINDS), which aims to understand the relation between the chemical inventory of protoplanetary disks and the properties of exoplanets. The results are not only providing the scientists with insight into the environment surrounding extremely young stars, but are also contributing to our understanding of the diversity of exoplanets, stars, and planetary systems.

As mentioned, planets typically form around stars via the material located within a protoplanetary disk. Scientists currently believe that terrestrial planets form more efficiently than gas giants when forming around extremely low-mass stars similar to the star Webb recently investigated. However, the compositions of these terrestrial planets are largely unknown. The new MINDS observations from Webb suggest that protoplanetary disks around low-mass stars evolve differently than disks around more massive stars, which could explain the difference in planetary composition.

In the new Webb observations, the telescope observed the area surrounding star ISO-Chal 147, which is extremely young and has a very low mass relative to other stars. The study’s results showed that the gas within ISO-Chal 147’s disk is rich in carbon, which could be due to carbon being removed from the solid material used to form rocky terrestrial planets like Earth. If this is true, it could explain why planets like Earth are relatively carbon-poor.

“Webb has a better sensitivity and spectral resolution than previous infrared space telescopes. These observations are not possible from Earth, because the emissions are blocked by the atmosphere. Previously we could only identify acetylene (C2H2) emission from this object. However, Webb’s higher sensitivity and spectral resolution allowed us to detect weak emissions from less abundant molecules. Webb also allowed us to understand that these hydrocarbon molecules are not just diverse but also abundant,” said lead author Aditya Arabhavi of the University of Groningen in the Netherlands.

The team investigated the contents of ISO-Chal 147’s disk using Webb’s Mid-Infrared Instrument (MIRI), which observed the disk in the mid-infrared and collected spectral data on it. From this data, the team constructed an emission spectrum of light that highlighted the elements and compounds present within the disk.

As aforementioned, Webb found the disk to contain the richest hydrocarbon chemistry to date within a protoplanetary disk, as the spectrum revealed the disk to contain 13 carbon-bearing molecules up to benzene. One of these molecules was ethane (C2H6), and its detection marks the first time the molecule has been detected outside of our solar system, as well as the largest fully-saturated hydrocarbon to ever be detected outside of our solar system. In addition to ethane, the team also identified ethylene (C2H4), propyne (C3H4), and the methyl radical CH3 for the first time in a protoplanetary disk.

Detecting fully saturated hydrocarbons around ISO-Chal 147 gives scientists additional insight into the chemical environment surrounding low-mass stars, as fully saturated hydrocarbons like ethane are expected to form from more basic molecules.

MIRI’s emission spectrum of ISO-Chal 147’s protoplanetary disk. (Credit: NASA/ESA/CSA/R. Crawford (STScI))

“These molecules have already been detected in our Solar System, for example in comets such as 67P/Churyumov–Gerasimenko and C/2014 Q2 (Lovejoy). 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,” Arabhavi explained.

Arabhavi et al. explain in the study that these results have large implications for the astrochemistry around young stars and in the inner 0.1 AU region around them, as well as for the planets forming there.

“This is profoundly different from the composition we see in discs around solar-type stars, where oxygen-bearing molecules dominate (like carbon dioxide and water). This object establishes that these are a unique class of objects,” said co-author Inga Kamp of the University of Groningen.

“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,” added co-author Agnés Perrin of Centre National de la Recherche Scientifique in France.

In the coming weeks and months, Arabhavi et al. hope to expand their study and plan to investigate more protoplanetary disks around other very low-mass stars similar to ISO-Chal 147. While Webb’s results from its observations of ISO-Chal 147 are telling and provide a great deal of insight into the environments around young stars, there are still hundreds of questions that remain unanswered. For example, scientists currently believe that carbon-rich protoplanetary disks are quite rare, so continuing to research these disks will develop scientists’ understanding of how common carbon-rich planet-forming areas are within the universe.

“The expansion of our study will also allow us to better understand how these molecules can form. Several features in the Webb data are also still unidentified, so more spectroscopy is required to fully interpret our observations,” added co-author Thomas Henning of the Max Planck Institute for Astronomy in Germany, who also serves as the principal investigator of the MINDS program.

Arabhavi et al.’s results were published in the journal Science. 

(Lead image: Artist’s impression of a protoplanetary disk. Credit: NASA/JPL-Caltech)

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