More than 3 billion miles from Earth, an ancient icy object is slowly awakening.
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 UCF Planetary Sciences Group 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.
"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.
