As it drifts inward through the solar system, the frozen body known as Centaur 450P/LONEOS has begun releasing gas and dust — behavior more commonly associated with comets than with Centaurs, the small icy objects that typically orbit between Jupiter and Neptune.

Now, researchers led by UCF Planetary Scientist and Associate Professor Charles Schambeau say they may be witnessing the early stages of a centaur transforming into a comet.

Using observations from NASA’s James Webb Space Telescope and the Gemini North telescope in Hawaii, scientists detected carbon dioxide gas, icy dust and signs of recent thermal activity surrounding 450P/LONEOS.  The findings, accepted for publication in the Planetary Science Journal, could provide new insight into how distant icy bodies evolve into active comets as they migrate inward through the solar system.

“Centaurs are scientifically important because they are thought to be transitional objects that originated farther out in the solar system and are slowly evolving toward becoming Jupiter-family comets. In that sense, they give us a way to study relatively primitive material from the outer solar system while it is beginning to respond to stronger solar heating.”

A Close Encounter with Saturn

Researchers believe 450P/LONEOS began “waking up” after a close gravitational encounter with Saturn in 1992 significantly altered its orbit.

The research team, which included Researcher Scientist Maria Womack and Professor Yan Fernandez and graduate student Aren Beck, found that the interaction moved the object inward from a more distant trajectory bringing its perihelion, the point in its orbit closest to the sun, closer to Jupiter.

As the centaur moved closer to the sun, researchers observed the gradual formation of a faint coma, a cloud of gas and dust surrounding the object commonly associated with cometary activity. Continued monitoring between 2019 and 2024 showed that the coma became increasingly visible as the object’s distance from the sun decreased.

“That increased solar heating can warm the surface and subsurface layers of the nucleus,” Schambeau says. “As those layers heat up, volatile ices or trapped gases can be released, which can drag dust away from the surface and produce a coma.”

Detecting Carbon Dioxide in Deep Space

One of the study’s most significant discoveries came from the James Webb Space Telescope, which detected carbon dioxide gas surrounding 450P/LONEOS at a distance where ordinary water ice would typically vaporize efficiently.

Researchers found strong evidence of carbon dioxide emission but no signs of water vapor or carbon monoxide, suggesting carbon dioxide is likely driving the centaur’s activity.

The observations also revealed icy dust grains within the coma, including possible signs of crystalline water ice — material that may preserve evidence of the object’s thermal evolution as it warms in its new orbit.

“The carbon dioxide detection was important because it directly identified one of the gases likely driving the activity,” Schambeau says. “At 450P’s distance from the sun, the nucleus is too cold for normal water-ice sublimation to be the main activity source, so detecting CO₂ gives us an important clue about what is powering the coma. The possible crystalline water ice is also interesting because it suggests that some of the ice in the coma has experienced heating or physical processing, rather than remaining completely unchanged since formation.”

Understanding How Comets Begin

Only a relatively small fraction of known centaurs show visible activity, making objects like 450P/LONEOS especially valuable  for studying how primitive icy bodies evolve over time.

The research suggests the object’s recent activity may be linked to warming beneath its surface. As buried amorphous ice — an irregular form of ice that traps gases inside its porous structure — warms and transforms into  crystalline ice, it releases carbon dioxide gas into space, carrying dust with it and creating the coma.

“Studying objects like 450P helps us connect different stages of small-body evolution.”— Charles Schambeau, research associate professor, Florida Space Institute

“We think this process may explain how 450P became active after its orbit changed and it began receiving more sunlight,” Schambeau says. “The released gas can escape through the porous nucleus and lift dust grains into the surrounding coma.”

Together, the findings may provide scientists with a better understanding of how distant icy bodies gradually evolve  into the active comets that periodically visit the inner solar system.

“Studying objects like 450P helps us connect different stages of small-body evolution,” Schambeau says. “Centaurs are likely related to trans-Neptunian objects, and some will eventually become short-period comets. By studying their activity, surface properties, and volatile composition, we can learn how comet nuclei change as they move inward through the solar system, how long they preserve primitive ices, and what physical processes turn an otherwise quiet icy body into an active comet.”

This research was supported by NASA’s Solar System Observations Program under award number 80NSSC23K0678, the Space Telescope Science Institute through award JWST-GO-02416 and the Florida Space Research Initiative.

Chiron belongs to the class of objects that astronomers call “Centaurs.” Centaurs are space objects that orbit the sun between Jupiter and Neptune. They are akin to the mythological creature they borrow their name from in that they are hybrid, possessing characteristics of both asteroids and comets.

Using the James Webb Space Telescope, UCF (FSI) scientists recently led a team that found, for the first time, that Chiron has surface chemistry unlike other centaurs. Its surface has both carbon dioxide and carbon monoxide ice along with carbon dioxide and methane gases in its coma, the cloud-like envelope of dust and gas surrounding it.

The researchers’ results were recently published in the journal .

UCF FSI Associate Scientist Noemí Pinilla-Alonso, who now works at the University of Oviedo in Spain, and Assistant Scientist Charles Schambeau led the research. The new findings build upon prior discoveries from Pinilla-Alonso and colleagues that detected carbon monoxide and carbon dioxide ice on trans-Neptunian objects (TNOs) for the first time earlier this year.

Those observations, paired with ones of Chiron, are creating foundational knowledge for understanding the creation of our Solar System, as these objects have largely remained unchanged since the Solar System was formed, Pinilla-Alonso says.

“All the small bodies in the Solar System talk to us about how it was back in time, which is a period of time we can’t really observe anymore,” she says. “But active centaurs tell us much more. They are undergoing transformation driven by solar heating and they provide a unique opportunity to learn about the surface and subsurface layers.”

Since Chiron possesses characteristics of both an asteroid and a comet, it makes it rich for studying many processes that could assist in understanding them, she says.

“What is unique about Chiron is that we can observe both the surface, where most of the ices can be found, and the coma, where we see gases that are originating from the surface or just below it,” Pinilla-Alonso says. “TNOs don’t have this kind of activity because they’re too far and too cold. Asteroids don’t have this kind of activity because they don’t have ice on them. Comets, on the other hand, show activity like centaurs, but they are typically observed closer to the sun, and their comas are so thick that they complicate the interpretations of observations of the ices on the surface. Discovering which gases are part of the coma and their different relationships with the ices on the surface help us learn the physical and chemical properties, such as the thickness and the porosity of the ice layer, its composition, and how irradiation is affecting it.”

The discovery of these ices and gases on an object as distant as Chiron – observed near its farthest point from the sun – is exciting because it could help contextualize other centaurs and provide insight into the earliest era of our Solar System, Schambeau says.

“These results are like nothing we’ve seen before,” he says. “Detecting gas comae around objects as far away from the sun as Chiron is very challenging, but JWST has made it accessible. These detections enhance our understanding of Chiron’s interior composition and how that material produces the unique behaviors as we observe Chiron.”

Schambeau specializes in studying centaurs, comets and other space objects. He analyzed the methane gas coma and determined that the outflowing gas detected was consistent with it being sourced from a surface area that was exposed to the most heating from the sun.

Chiron, first discovered in 1977, is characterized much better than most centaurs and comparatively is unique, Schambeau says. The newly analyzed information helps scientists better understand the thermophysical process going on in Chiron that produces methane gas, he says.

“It’s an oddball when compared to the majority of other Centaurs,” Schambeau says. “It has periods where it behaves like a comet, it has rings of material around it, and potentially a debris field of small dust or rocky material orbiting around it. So, many questions arise about Chiron’s properties that allow these unique behaviors.”

The researchers concluded that the coexistence of the molecules in various states adds another layer of intrigue for studying comets and centaurs. The study also highlighted the presence of irradiated byproducts of methane, carbon monoxide and carbon dioxide that will require further research and could help scientists further reveal the unique processes producing Chiron’s surface composition.

Chiron originated from the TNO region and has traveled around our Solar System since its creation, says Pinilla-Alonso. The orbits of Chiron and many other large non-planetary objects occasionally experience close encounters with one of the giant planets where the gravitational pull from the planet changes the smaller object’s orbit, taking them all over our Solar System and exposing them to many different environments, she says.

“We know it has been ejected from the TNO population and is only now transiting through the region of the giant planets, where it will not stay for too long,” Pinilla-Alonso says. “After about 1 million years, centaurs like Chiron typically are ejected from the giant planets region, where they may end their lives as Jupiter Family comets or they may return to the TNOs region.”

Pinilla-Alonso notes that the JWST’s spectra showed for the first time Chiron’s plethora of ices with different volatilities and their formation processes, she says.

Some of these ices, such as methane, carbon dioxide, and water ice, may be primordial components of Chiron inherited from the pre-solar nebula. Others, such as acetylene, propane, ethane, and carbon oxide, could have formed on the surface because of reduction and oxidation processes, she says.

“Based on our new JWST data, I’m not so sure we have a standard centaur,” Pinilla-Alonso says. “Every active centaur that we are observing with JWST shows some peculiarity. But they cannot be all outliers. There must be something that explains why they appear to all behave differently or something that is common between them all that we cannot yet see.”

The analysis of Chiron’s gases and ices opens new frontiers and opportunities for exciting research, she says.

“We’re going to follow up with Chiron,” Pinilla-Alonso says. “It will come closer to us, and if we can study it at nearer distances and get better reads on the quantities and nature of the ices, silicates, and organics, we will be able to better understand how seasonal insolation variations and different illumination patterns can affect its behavior and its ice reservoir.”

The JWST is the world’s premier space science observatory, and it is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe. The JWST is an international collaboration led by NASA with its partners the European Space Agency and the Canadian Space Agency.

Researchers’ Credentials

Pinilla-Alonso was a professor at FSI who joined UCF in 2015. Most of her work on this project was conducted while she was at UCF. Pinilla-Alonso also holds a joint appointment as a research professor in UCF’s  and has led numerous international observational campaigns in support of NASA missions, such as New Horizons, OSIRIS-REx and Lucy. Pinilla-Alonso is a distinguished professor at the Institute for Space Sciences and Technologies in Asturias, within the Universidad de Oviedo. She received her doctoral degree in astrophysics and planetary sciences from the Universidad de La Laguna in Spain.

Schambeau is an assistant scientist who received his doctoral degree in physics with a concentration in planetary sciences in 2018 from UCF. He subsequently joined FSI where he expanded upon his work examining comets and centaurs as part ɫ����’s .

The work will inform research into the origins of the solar system, as these bodies contain materials from the dawn of its formation.

Centaurs and Jupiter-family comets are small icy bodies that exist primarily in the outer regions of the solar system. While both are composed of a mixture of rock, dust and volatile substances, Jupiter-family comets are known for their cometary activity, such as comae and tails, while centaurs are often considered dormant. However, about 10% of known centaurs do display cometary-like activity.

“Centaurs and Jupiter-family comets have material in their nuclei interiors that we think is pretty pristine in the sense that their upper layers are really insulating, so the solar heating that’s incident on their surfaces doesn’t penetrate very deep,” says Charles Schambeau ’18PhD, an assistant scientist with UCF’s and the project’s principal investigator. “And so, if we can try to understand their interiors more, we will have a connection to that early, four-and-a-half billion-year-old set of conditions when they formed.”

The four-year, $500,000 NASA-funded project will use the Gemini Observatory’s twin 8.1-meter telescopes located in Chile and Hawaii to make observations of approximately 60 distantly active small icy bodies.

Schambeau and project co-investigator UCF Professor Yan Fernandez have been leading a data collection effort of these objects since 2016, which is resulting in the largest and most comprehensive set of high-quality data on these types of objects to date. Receiving the new NASA award will enable the continuation of their program at least until 2026, Schambeau says.

The project team also includes collaborator Marco Micheli, a researcher with the European Space Agency.

Investigating Icy Bodies

The researchers will specifically investigate how the super volatiles carbon monoxide (CO) and carbon dioxide (CO₂) are stored in the icy bodies, which remains a fundamental knowledge gap in the understanding of the formation and evolution of the solar system, Schambeau says.

If CO and CO₂ are found to be frozen as bulk ices in Centaur nuclei interiors, then it means they were formed in a much colder environment than if CO and CO₂ are found to be trapped inside of a porous form of ice known as amorphous water ice. For instance, if they are found to be frozen as bulk ice, the objects could have formed much farther from the Sun.

“The current state of super volatiles in these objects really gives a good constraint on the temperature under which these objects formed, and that gives us vital constraints that can be later used in solar system formation models,” Schambeau says.

The project so far has been amassing a large amount of imaging data on each individual object.

“One major goal of the project is to monitor each object’s comet-like activity behaviors over the course of an entire orbit around the Sun, which for centaurs can at times take decades,” he says. “We’re really in this for the long haul.”

Student Researchers

The large amount of data collected over a long time period has resulted in the project enlisting UCF undergraduate students to help develop software to streamline the data’s processing.

Recent UCF physics graduates Tina Beck ’23 and Seamus Walker ’23 have been working on the project since the fall of 2021 by helping with the data’s processing pipeline.

Both became interested in the work after they had been students in Schambeau’s astronomy class as undergraduates.

“I had a NASA internship during the summer of 2020 working with the preparations for the James Webb Space Telescope where I was exposed to an abundance of information regarding instrumentation, observation taking and data processing,” Beck says. “My interest in these subjects only grew as a result, leading me to pursue a better understanding of how we get from images to knowledge.”

“Upon hearing more about Dr. Schambeau’s research, I knew working with him would allow me to explore observational astronomy more deeply,” she says. “My interests in centaurs and cometary evolution developed as a direct result of working with him.”

Walker says working on the project has been a wonderful experience.

“This project has helped me grow during the course of my education at UCF, and I’ve learned so much because of it,” Walker says. “Working with specific objects becomes personal, and you get invested in looking at the data and figuring out more about each one.”

Beck and Walker’s work has focused on helping develop a software suite that converts raw images from telescopic observations into science-quality data ready for analysis, as well as beginning to characterize some of the objects they are studying.

“When you get these raw observations, there’s a lot of noise in them,” Walker says. “For example, high-energy particles might have hit your detector leaving you with streaks in the image. Our code helps to remove those artifacts and boost the signal we have for the objects that we’re interested in studying.”

Beck says the work has been fascinating and is the highlight of her undergraduate education at UCF.

“Centaurs are a body that as a community we do not fully understand, but they possess information that can help us unlock a better understanding of cometary evolution and thereby solar system evolution,” she says. “I thoroughly enjoy learning from Dr. Schambeau and the rest of the team.”

Future Observations

The team’s research using the Gemini Observatory is paving the way to incorporate future observations they will have from the upcoming Vera Rubin Observatory in Chile, which is scheduled to begin operations in mid 2025.

Rubin’s Legacy Survey of Space and Time (LSST)  will provide almost nightly imaging data for many of the centaurs included in our program, Schambeau says.

“With the current Gemini Observations, the team has dedicated observations made of each specific icy body about twice a year, so the windfall of new data from the LSST is something the team is preparing for,” he says.

Researcher Credentials

Schambeau began the large and long-term observing campaign of centaurs and Jupiter-family comets as part of a NASA fellowship he received while a physics doctoral student in UCF’s Department of Physics. He received his doctorate in physics with a concentration in planetary sciences from UCF in 2018 and subsequently joined the Florida Space Institute where he continued the work as part ɫ����’s . The funding for the new work is through NASA’s Shared Services Center.

Fernandez received his doctorate in astronomy from the University of Maryland, College Park. He spent 3-years (1999-2002) as a Scientific Researcher and 3-years (2002-2005) as a SIRTF/Spitzer Fellow in University of Hawai’i before joining UCF in 2005, where he is a professor in UCF’s Department of Physics, part ɫ����’s .