Scientists recently led a team that discovered, for the first time, that Chiron has unique surface chemistry that distinguishes it from other centaurs. Its surface consists of both carbon dioxide and carbon monoxide ice, and it contains carbon dioxide and methane gases in its coma, which is the cloud-like envelope of dust and gas surrounding it.
Even though our Solar System is billions of years old, we are only now becoming more familiar with one of its most interesting and dynamic inhabitants, known as (2060) Chiron.
Chiron is classified as a “Centaur,” a term used by astronomers to refer to celestial bodies that orbit the Sun between Jupiter and Neptune. Similar to the mythological centaur, these objects have mixed characteristics of both asteroids and comets.
With the aid of the James Webb Space Telescope, scientists from the UCF Florida Space Institute (FSI) recently uncovered that Chiron possesses a surface chemistry that is different from that of other centaurs. Specifically, its surface includes both carbon dioxide and carbon monoxide ice, and its coma is rich in carbon dioxide and methane gases.
The findings were recently published in the journal Astronomy & Astrophysics.
UCF FSI Associate Scientist Noemà Pinilla-Alonso, who is now at the University of Oviedo in Spain, and Assistant Scientist Charles Schambeau spearheaded the research. Their latest results build on earlier findings where Pinilla-Alonso and her team detected carbon monoxide and carbon dioxide ice on trans-Neptunian objects (TNOs) for the first time this year.
These observations, along with those of Chiron, are contributing to foundational knowledge that can help us understand the origins of our Solar System, as these celestial bodies have largely remained unchanged since its formation, according to Pinilla-Alonso.
“All the small bodies in the Solar System provide insight into how things were in the past, a time we can no longer directly observe,” she explains. “However, active centaurs reveal even more. They are undergoing changes driven by solar heating, offering us a unique chance to study their surface and subsurface layers.”
Chiron’s characteristics, which reflect both asteroid and comet traits, make it particularly valuable for studying various processes that may help us comprehend these objects more thoroughly, she adds.
“Chiron is unique because we can examine both its surface, where most ice resides, and its coma, which contains gases coming from the surface or just below it,” Pinilla-Alonso asserts. “TNOs lack this activity as they are too distant and too cold. Asteroids don’t have such activity because they don’t contain ice. Comets, while active like centaurs, are usually observed closer to the Sun, and their dense comas complicate the interpretation of surface ice observations. Identifying the gases present in the coma and how they interact with the surface ices aids in our understanding of the physical and chemical properties, such as the ice layer’s thickness, porosity, composition, and the effects of irradiation.”
Discovering these ices and gases on such a distant object as Chiron—observed at its farthest point from the Sun—is thrilling, as it may offer context for other centaurs and insights into the early days of our Solar System, according to Schambeau.
“These findings are unprecedented,” he says. “Detecting gas comae around objects as far from the Sun as Chiron is quite difficult, but the JWST has made this possible. These detections improve our understanding of Chiron’s internal structure and how that material results in its observed unique behaviors.”
Schambeau specializes in the study of centaurs, comets, and other celestial bodies. He investigated the methane gas coma and found that the detected gas flow was consistent with it originating from areas on the surface that were warmed most by the Sun.
Chiron, which was discovered in 1977, is much better characterized than most centaurs and is notably unique, according to Schambeau. The new data allows scientists to gain a deeper understanding of the thermophysical processes occurring on Chiron that produce methane gas.
“When compared to most other centaurs, it stands out,” Schambeau remarks. “It exhibits behavior similar to a comet at times, has rings of material surrounding it, and potentially contains a field of small dust or rocky materials in orbit around it. This raises numerous questions regarding the properties of Chiron that enable these eccentric behaviors.”
The researchers concluded that the presence of various molecules in different states adds further interest to the study of comets and centaurs. The research also emphasized the presence of irradiated byproducts of methane, carbon monoxide, and carbon dioxide, which warrant additional study and could aid scientists in uncovering the unique processes that contribute to Chiron’s surface composition.
Chiron originated from the TNO region and has traversed our Solar System since its formation, as explained by Pinilla-Alonso. The orbits of Chiron and many other large non-planetary bodies occasionally intersect with those of giant planets, causing gravitational influences that alter their orbits and expose them to various environments.
“We know Chiron has been ejected from the TNO population and is currently transitioning through the region of the giant planets, although it won’t remain there for long,” Pinilla-Alonso explains. “Typically, after about 1 million years, centaurs like Chiron are expelled from the giant planets’ region, where they might become Jupiter Family comets or return to the TNO region.”
Pinilla-Alonso points out that the JWST’s spectral data has revealed Chiron’s array of ices with varying volatility and their formation processes for the first time.
Some of these ices, like methane, carbon dioxide, and water ice, may be primordial components inherited from the pre-solar nebula. Others, including acetylene, propane, ethane, and carbon oxide, may have formed on the surface via reduction and oxidation processes, she notes.
“Based on our new JWST findings, I’m unsure we have a typical centaur,” Pinilla-Alonso states. “Every active centaur we observe with JWST exhibits some unique feature. However, they cannot all be anomalies. There must be an underlying reason for their different behaviors or some commonality among them that we have yet to discern.”
The examination of Chiron’s gases and ices unveils new possibilities for exciting research, according to her.
“We intend to continue our studies on Chiron,” Pinilla-Alonso confirms. “It will approach closer to us, and if we can observe it at nearer distances and analyze the quantities and nature of its ices, silicates, and organics, we will gain a better understanding of how seasonal variations in sunlight and distinct illumination patterns influence its behavior and ice reservoir.”
The JWST is the leading space science observatory globally, addressing mysteries in our solar system, exploring distant worlds around other stars, and examining the complex structures and origins of our universe. It is a collaborative project led by NASA with contributions from the European Space Agency and the Canadian Space Agency.
Researchers’ Credentials
Pinilla-Alonso is a former professor at FSI who joined UCF in 2015. Much of her work on this project was conducted during her time at UCF. She also has a research professorship in UCF’s Department of Physics and has led numerous international observational campaigns supporting NASA missions such as New Horizons, OSIRIS-REx, and Lucy. She is a distinguished professor at the Institute for Space Sciences and Technologies in Asturias at the Universidad de Oviedo. Pinilla-Alonso earned her doctoral degree in astrophysics and planetary sciences from the Universidad de La Laguna in Spain.
Schambeau is an assistant scientist who completed his doctoral degree in physics with a specialization in planetary sciences from UCF in 2018. After that, he joined FSI to further develop his work on exploring comets and centaurs as part of UCF’s Preeminent Postdoctoral Program.
