Astronomers have captured a rare celestial transformation: an icy body orbiting beyond Jupiter is actively evolving into a comet. The object, designated 450P/LONEOS, represents a critical missing link between dormant centaurs and the active Jupiter-family comets that cross their paths.
Discovered in 2004 by the Lowell Observatory Near-Earth-Object Search, 450P is classified as a centaur—a class of inactive objects that orbit between Jupiter and Neptune. These bodies are believed to originate in the Kuiper Belt beyond Pluto, with their trajectories altered by gravitational interactions with giant planets or passing stars. Over millions of years, these unstable orbits can push centaurs closer to the sun, where they are hypothesized to transform into Jupiter-family comets, defined by orbital periods under 20 years. However, no centaur has ever been directly observed undergoing this specific transition.
Currently orbiting the sun every 22 years, 450P is not yet a Jupiter-family comet, but researchers led by Charles Schambeau of the University of Central Florida have detected the onset of cometary activity. Using the Gemini North telescope in Hawaii, the team observed a growing coma—a cloud of gas and dust—around the object’s solid nucleus between 2019 and 2024, intensifying as the object reached perihelion.
The trigger for this activation appears to be a close encounter with Saturn in 1992. Orbital tracking indicates the centaur passed within 2.9 million miles (4.6 million kilometers) of the planet, significantly shortening its orbital period and bringing its perihelion to 5.4 astronomical units, just beyond Jupiter’s orbit. This proximity subjected the nucleus to increased solar heating, causing volatile ices to release gas and drag dust into space.
Data from the James Webb Space Telescope (JWST) provided further insight into the composition of the emerging coma. Researchers detected carbon dioxide gas but found a complete absence of water vapor. Schambeau noted that at 450P’s distance from the sun, the nucleus remains too cold for water-ice sublimation to be the primary driver of activity, identifying carbon dioxide as the powering force.
Additionally, JWST identified hints of crystalline water-ice particles. While pristine Kuiper Belt ice is typically amorphous, the presence of crystalline structures suggests the ice has undergone thermal processing. As the object warms, amorphous ice transitions into a more regular crystalline form, releasing trapped gases that carry dust and ice particles into the coma.
“Studying objects like 450P helps us connect different stages of small-body evolution,” Schambeau stated. “By studying their activity, surface properties and volatile composition, we can learn how comet nuclei change as they move inward through the solar system.”
Because only a tiny fraction of centaurs exhibit such activity, 450P’s recent perihelion offers a unique opportunity to study primitive material from the outer solar system as it begins to respond to stronger solar heating. The findings have been accepted for publication in the Planetary Science Journal and are available on the arXiv pre-print archive.
Finally, actual proof of the missing link between centaurs and comets. This is huge for understanding our solar system’s history!
No water vapor? Interesting. I wonder if we’ve been underestimating CO2-driven activity in the outer solar system.