Astronomers have watched a small centaur object known as 450P/LONEOS transform into a comet far away, providing a missing link in understanding how inactive icy bodies evolve as they move toward the sun, according to observations made by the Gemini North telescope and the James Webb Space Telescope.
Tracking the Transformation of Centaur 450P/LONEOS
Deep in the outer solar system, a distant icy wanderer is making the leap from an inert centaur into an active comet. Originally discovered in 2004 by the Lowell Observatory survey, the object designated as 450P/LONEOS orbits the sun between Jupiter and Neptune. Centaurs are believed to originate in the Kuiper Belt beyond Pluto before gravitational nudges from gas giant planets or passing stars send them wandering inward.
Because these objects cross the paths of giant planets, their trajectories remain unstable over millions of years. Scientists have long suspected that centaurs pushed closer to the sun eventually evolve into Jupiter-family comets, which possess orbital periods of less than 20 years. Until now, astronomers had never seen a centaur turn into a Jupiter-family comet. While 450P currently carries an orbital period of 22 years—putting it just outside the definition of a Jupiter-family comet—planetary researchers led by Charles Schambeau of the University of Central Florida have observed the onset of active comet behavior.
A Close Encounter With Saturn Sparked the Shift
The celestial mechanics behind this awakening trace back to a planetary encounter. By tracking the object’s orbit backward prior to its 2004 discovery, researchers determined that 450P came within 2.9 million miles of Saturn in 1992. That gravitational interaction shortened the object’s orbit significantly, placing its perihelion—the closest point to the sun—at 5.4 astronomical units, or roughly 506 million miles, just outside Jupiter’s orbit.
Following that orbital adjustment, 450P arrived at perihelion in August 2024, absorbing substantially more solar heat than it has in the past. That thermal influx penetrated both the surface and subsurface layers of the icy nucleus, triggering outgassing that dragged dust away from the body to form a visible cloud of gas and dust known as a coma.
“That increased solar heating can warm the surface and the subsurface layers of the nucleus. 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.”
Charles Schambeau, planetary scientist at the University of Central Florida, via Space
Carbon Dioxide Drives Activity While Water Vapor Stays Absent
To understand the mechanisms powering this burgeoning coma, the research team turned to the James Webb Space Telescope. Spectral analysis revealed a chemical signature: the coma contained carbon dioxide gas alongside hints of crystalline water-ice and dust, but showed a complete absence of water vapor. At 450P’s distance from the sun, the nucleus remains too cold for standard water-ice sublimation to drive activity.
Instead, researchers point to carbon dioxide as the primary engine behind the transformation. Furthermore, the detection of crystalline water-ice suggests that parts of the material experienced prior heating or physical processing, departing from the amorphous state typically found in untouched Kuiper Belt objects where frozen water molecules lack a structured arrangement.
“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 carbon dioxide gives us an important clue about what is powering the coma.”
Charles Schambeau, planetary scientist at the University of Central Florida, via Space
Connecting Small-Body Evolution Across the Solar System
Observing 450P through the Gemini North telescope in Hawaii allowed astronomers to watch its coma brighten between 2019 and 2024 as it approached perihelion. Researchers note that if the object maintains its trajectory and receives one more gravitational nudge from a giant planet, it could formally transition into a Jupiter-family comet.
This transition offers a window into how primitive ices survive and transform as small bodies migrate inward. By connecting centaurs directly to short-period comets, scientists gain empirical data on the physical processes that turn dormant, icy rocks into active celestial visitors.
“Studying objects like 450P helps us connect different stages of small-body evolution,” said Schambeau in a statement. “Centaurs are likely related to trans-Neptunian objects, and some will eventually become short-period comets. By studying their activity, surface properties and volatile [substances with low boiling or sublimation points such as water and carbon dioxide] 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.”
Charles Schambeau, planetary scientist at the University of Central Florida, via Space
