Centaurs — celestial bodies that combine asteroids’ rockiness and comets’ gaseousness — are relatively rare and short-lived components of our solar system. A team of astronomers has in one of these hybrid objects called Chiron now characterized what could be considered a unicorn among centaurs.
Learning About Centaurs
Chiron contains signs that it has emitted both carbon dioxide and methane — the first time the two gasses were found released from a Trans-Neptunian Object (TNO), a team of scientists report in the journal Astronomy & Astrophysics. Chiron’s chemical composition is unique in that carbon dioxide and carbon monoxide ice are part of its surface, while carbon dioxide and methane gas are part of its “coma” — a cloud-like collection of dust and gases that surround it.
TNOs are any small body that orbits the sun from a greater distance than Neptune — sometimes crossing a planet’s pathway. All centaurs are TNOs, but not all TNOs are centaurs. For example, Pluto is considered a TNO but not a centaur.
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A Rare Sighting
A University of Central Florida (UCF) Florida Space Institute team used the James Webb Space Telescope to go centaur hunting. They analyzed the chemical composition of 59 TNOs and centaurs and found that only Chiron contained that particular combination of gases.
They found ample amounts of carbon dioxide in 56 of the TNOs, as well as carbon monoxide in 28. Carbon monoxide only showed up in the objects with the highest concentration of carbon dioxide.
“It is the first time we observed this region of the spectrum for a large collection of TNOs, so in a sense, everything we saw was exciting and unique,” Mário Nascimento de Prá, an author of the study and member of the Florida Space Institute team, said in a press release. “We did not expect to find that carbon dioxide was so ubiquitous in the TNO region.”
‘Leftovers’ of the Early Solar Systems
Studying the gases trapped within TNO ice provides clues to the solar system’s origins. The research suggests that carbon dioxide was especially abundant in the cold outer edges of the massive rotating disc of dust and gases from which the solar system emerged.
Scientists have only recently gained this level of access to centaurs’ chemical components. The Webb, which was launched Christmas 2021, essentially provided the tools necessary to take a closer look. An earlier study spotted unusual jets of case shooting from another centaur, 29P.
“Centaurs can be considered as some of the leftovers of our planetary system’s formation, Sara Faggi, a scientist with NASA’s Goddard Space Flight Center and an author of the 29P Nature Astronomy paper, said in a press release. “Because they are stored at very cold temperatures, they preserve information about volatiles in the early stages of the solar system. Webb really opened the door to a resolution and sensitivity that was impressive to us — when we saw the data for the first time, we were excited. We had never seen anything like this.”
Expect to see and hear more about centaurs in the coming years.
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Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
