Key Takeaways
• Astronomers detected an atmosphere on 2002 XV93, a small icy object beyond Neptune
• It is only the second Kuiper Belt object after Pluto known to have an atmosphere
• The atmosphere is extremely thin, millions of times less dense than Earth’s
• The finding challenges assumptions about small bodies holding atmospheres
• Scientists believe the atmosphere may be actively replenished
Astronomers have made a surprising discovery in the outer reaches of the solar system, detecting a thin atmosphere surrounding (612533) 2002 XV93, a small icy body orbiting far beyond Neptune.
The finding, published in Nature Astronomy, challenges long standing assumptions about which types of objects can sustain atmospheres. Until now, such features were thought to be limited to larger bodies like planets, dwarf planets, and certain moons.
The discovery was made using a technique known as a stellar occultation. On January 10, 2024, the object passed in front of a distant star as seen from Earth. A research team led by Ko Arimatsu observed the event using multiple telescopes across Japan.
Instead of the starlight disappearing abruptly as the object moved across it, the light dimmed gradually. This subtle fading indicated that the light was being bent and filtered through a thin layer of gas, confirming the presence of an atmosphere.
Despite its existence, the atmosphere is extremely fragile. Scientists estimate it is between five million and ten million times less dense than Earth’s atmosphere, and far thinner than that of Pluto. It is likely composed of gases such as methane, nitrogen, or carbon monoxide.
What makes this discovery particularly remarkable is the size of the object. At roughly 500 kilometers in diameter, 2002 XV93 is significantly smaller than Pluto and may be the smallest known body in the solar system capable of holding a global atmosphere through gravity alone.
The object belongs to a class known as plutinos, which share a unique orbital relationship with Neptune. It completes two orbits around the Sun for every three orbits of Neptune, traveling at a distance about 40 times farther from the Sun than Earth.
The presence of such a delicate atmosphere raises an important question. How is it being maintained? Models suggest that the gas should escape into space within a relatively short timespan, potentially just a few hundred to a thousand years.
Researchers have proposed two possible explanations. One is that a recent impact from a comet or other object released trapped gases into space, temporarily forming the atmosphere. The other possibility is ongoing cryovolcanism, where icy material from the interior erupts and releases gases continuously.
Observations from NASA’s James Webb Space Telescope have so far failed to detect frozen surface gases that would normally feed such an atmosphere, adding to the mystery.
Future observations will be key to solving this puzzle. If the atmosphere fades over time, it would support the idea of a recent impact event. If it remains stable or shows seasonal changes, it could point to internal processes actively replenishing the gas.
This discovery expands our understanding of the diversity of worlds in the solar system and suggests that even small, distant objects may be more dynamic than previously believed.