This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: More than 3 billion miles (4.8 billion kilometers) 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, published 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." 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 Research Scientist Maria Womack, 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." 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." 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.
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