Astronomers closely observed the transformation of the icy 450P/LONEOS, orbiting beyond Jupiter, into a comet. Discovered in 2004, the Centaur is on an unstable orbit between Jupiter and Neptune and is thought to have been pushed into the inner Solar System from the Kuiper Belt by the gravity of the giant planets. As the object approached the Sun and warmed, a coma made up of gas and dust formed around it; the structure brightened markedly in 2019-2024. With an orbital period of 22 years, 450P is not yet considered a Jupiter Family comet. Its approach to within approximately 4.6 million km of Saturn in 1992 shortened its orbit. The object passed perihelion in August 2024 and began releasing gas. James Webb showed that the activity was caused by carbon dioxide. Crystallized water-ice particles revealed that the primordial structure had changed.
Why it matters
These observations are important for understanding how icy objects that remain cold and relatively inactive in the outer Solar System become active when they approach the Sun. Carbon dioxide-driven outgassing and crystallized water-ice particles indicate not merely a temporary brightening on the surface, but changes occurring in the object’s primordial structure as it warms. The fact that its past close approach to Saturn altered its orbit also reveals the influence of giant planets on the trajectories and classification of such objects. The open question is whether other icy objects that have undergone similar orbital changes also pass through the same process and under what conditions they will be considered comets.