This artist's rendition illustrates a young star enveloped by a disk of gas and dust. Utilizing NASA’s James Webb Space Telescope, an international team of astronomers has delved into the disk surrounding a young, exceptionally low-mass star identified as ISO-ChaI 147. Their investigation has unveiled the most extensive hydrocarbon chemistry observed thus far in a protoplanetary disk. These findings, published in Science, shed light on the potential composition of planets that may form around this particular star.


Implications for Planet Formation

Rocky planets are more probable around low-mass stars compared to gas giants, making them prevalent around the most common stars in our galaxy. Yet, there's limited knowledge about the chemistry of such planets, which might resemble or differ significantly from Earth. By examining the disks from which these planets emerge, astronomers aim to enhance their understanding of the planet formation process and the compositions of resulting planets.


Studying planet-forming disks around very low-mass stars poses challenges due to their smaller size and fainter nature compared to disks around high-mass stars. The Mid-Infrared Disk Survey (MINDS) program, leveraging Webb's unique capabilities, endeavors to bridge the gap between the chemical composition of disks and the properties of exoplanets.


Lead author Aditya Arabhavi from the University of Groningen, Netherlands, notes, "Webb's superior sensitivity and spectral resolution enable observations impossible from Earth, where atmospheric interference blocks emissions from the disk." In their recent study, the team explored the vicinity of the very low-mass star ISO-ChaI 147, which is approximately 1 to 2 million years old and only 0.11 times the mass of the Sun. The spectrum captured by Webb's Mid-Infrared Instrument (MIRI) reveals the richest hydrocarbon chemistry yet observed in a protoplanetary disk, encompassing a total of 13 distinct carbon-bearing molecules. This includes the first detection of ethane (C2H6) beyond our solar system, alongside ethylene (C2H4), propyne (C3H4), and the methyl radical CH3.


"These molecules, previously identified in our solar system within comets like 67P/Churyumov–Gerasimenko and C/2014 Q2 (Lovejoy), are not only diverse but also abundant," adds Arabhavi. "It's remarkable that we can now witness the interplay of these molecules in the cradles of planets. This environment for planet formation is vastly different from what we typically imagine."


The team suggests that these findings hold significant implications for the chemistry of the inner disk and the potential compositions of planets that may form within it. The abundance of carbon-rich gas revealed by Webb suggests a scarcity of carbon in the solid materials from which planets would emerge, indicating that planets in this region may ultimately possess low carbon content—an attribute distinct from Earth's composition.


Inga Kamp, a team member from the University of Groningen, underscores the uniqueness of this discovery, stating, "This object highlights a unique class of objects distinct from disks around solar-type stars, where oxygen-bearing molecules like water and carbon dioxide dominate."


Agnés Perrin, a team member from Centre National de la Recherche Scientifique, France, adds, "It's astounding that we can quantify the presence of familiar molecules like benzene in an object situated over 600 light-years away."


Moving forward, the science team aims to expand their investigation to a broader array of disks around very low-mass stars to gain a deeper understanding of the prevalence and characteristics of carbon-rich terrestrial planet-forming regions. Thomas Henning, principal investigator of the MINDS program from the Max-Planck-Institute for Astronomy, Germany, underscores the necessity for additional spectroscopic analysis to fully interpret their observations.


Moreover, this work underscores the importance of interdisciplinary collaboration, with the team emphasizing that their results and accompanying data can contribute to various fields, including theoretical physics, chemistry, and astrochemistry, facilitating the interpretation of spectra and the exploration of new features within this wavelength range.