The Webb Space Telescope finds an abundance of carbon molecules around a young star

"It's amazing that we can detect and quantify the amount of molecules we know very well on Earth, like benzene, which is actually more than 600 light-years away," said one of the authors of the paper that appeared in Science

Artist's impression of a protoplanetary disk. Credit: ESA
Artist's impression of a protoplanetary disk. Credit: ESA

An international team of astronomers used NASA/ESA's James Webb Space Telescope to study the disk around a young, very low-mass star. The results reveal the richest hydrocarbon chemistry yet observed in a protoplanetary disk (including the first discovery outside the solar system of Ethan). and contribute to our evolving understanding of a variety of planetary systems.

Planets form in disks of gas and dust surrounding young stars. Observations show that terrestrial planets are likely to form more efficiently from gas giants in disks around very low-mass stars. While very low-mass stars have the highest occurrence rate of rocky planets orbiting them, their planetary compositions are largely unknown. For example, the Trappist-1 system studied by Webb consists of seven rocky planets within 0.1 astronomical units (au) and its composition is generally assumed to be Earth-like. However, new data from Webb suggests that disks around very low-mass stars may evolve differently from disks around more massive stars.

MIRI's MID-INfrared Disk Survey (MINDS) aims to bridge the gap between the presence of disks and the properties of extrasolar planets. In this new study, the team studied the region around a very low-mass star of 0.11 solar masses (known as ISO-ChaI 147). These observations provide insights into the environment as well as basic ingredients for the formation of planets. The team found that the gas in the star-forming region of the star is rich in carbon. This may be because the carbon has been removed from the solid material from which rocky planets can form, which could explain why Earth is relatively low in carbon.

"The WEB has better sensitivity and spectral resolution than previous infrared space telescopes," explained lead study author Aditya Arabi of the University of Groningen in the Netherlands. "These observations are not possible from Earth, because the emissions are blocked by the atmosphere. Previously, we could only detect emissions of acetylene (C2H2) from this object. However, the high sensitivity and spectral resolution of 'Web' allowed us to detect weak emissions from molecules poorer in carbon. Webb also allowed us to understand that these hydrocarbon molecules are not only diverse but also abundant and richer in carbon."

The spectrum revealed by Webb's MIRI instrument shows the richest hydrocarbon chemistry yet seen in a protoplanetary disk, including 13 carbon-bearing molecules up to benzene. This includes the first extrasolar discovery of ethane (C2H6), the largest fully saturated hydrocarbon found outside our solar system. Because saturated hydrocarbons are expected to form from more basic molecules, their detection here gives researchers clues about the chemical environment. The team also successfully detected ethylene (C2H4), propene (C3H4) and the methyl radical CH3, for the first time in a protoplanetary disk.

"These molecules have already been discovered in our solar system, for example in comets like 67P/Churyumov-Gerasimenko and C/2014 Q2 (Lovejoy)," Arabbi adds. "The fascinating chemistry created in new stars". It's a very different environment than what we normally think of as suitable for planet formation."

The team notes that these results have major implications for astrochemistry within 0.1 AU and the stars that form there. "This is fundamentally different from the composition we see in disks around solar-type stars, where oxygen-carrying molecules dominate (such as carbon dioxide and water)," added team member Inge Kamp, also from the University of Groningen. "This bone proves that this is a unique type of object."

"It's amazing that we can detect and quantify the amount of molecules we know very well on Earth, like benzene, which is actually more than 600 light-years away," added team member Anneise Perrin of the National Research Center in France.

Next, the research team intends to expand their study to a larger sample of disks around very low-mass stars to develop their understanding of how common carbon-rich exotic regions are for the formation of terrestrial planets. "Expanding our research will also allow us to better understand how these molecules can form," explained team member and MINDS program manager Thomas Henning of the Max Planck Institute for Astronomy in Germany. "Several features in the Webb data are still unidentified, so further spectroscopy is required to fully interpret our observations."

This work also highlights the critical need for scientists to collaborate across disciplines. The team notes that these results and the accompanying data can contribute to other fields including theoretical physics, chemistry and astrochemistry, to interpret the spectrum and explore new properties in this wavelength range.

These findings were published in the journal Science.

https://esawebb.org/news/weic2416/?lang

Comments

[1] An astronomical unit (AU, or au) is a unit of length roughly equal to the average distance between the Earth and the Sun, defined as approximately 150 million kilometers.

[2] Saturated hydrocarbons are molecules composed entirely of single carbon-carbon bonds. They cannot incorporate additional atoms into their structure, so they are considered saturated.

for the scientific article

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