For the first time, astronomers have detected a thin atmosphere around a small trans-Neptunian object, revealing recent activity in the distant Kuiper Belt.
A team of professional and amateur astronomers in Japan has detected a thin atmosphere around the trans-Neptunian object (TNO) (612533) 2002 XV93, marking the first time such a feature has been identified on a small TNO. The finding was published in Nature Astronomy.
Observation Method
On January 10, 2024, the object, approximately 500 km (311 miles) in diameter, passed in front of a 15-magnitude star in an event known as a stellar occultation. Observations were conducted from four sites in Japan.
The star's brightness faded gradually over approximately 1.5 seconds, indicating the presence of an atmosphere that refracted the starlight. An abrupt disappearance would have been expected if no atmosphere were present.
Atmosphere Characteristics
The atmosphere, described as an exosphere, has a surface pressure of 100–200 nanobars. This is estimated to be 5 to 10 million times thinner than Earth's atmosphere at sea level.
The composition of the atmosphere has not been determined. The object's surface temperature (40–50 K) rules out sublimation of water or carbon dioxide ices. The James Webb Space Telescope has not detected frozen gases—such as nitrogen, methane, or carbon monoxide—on the surface that could sublimate to sustain the atmosphere.
Possible Explanations
Two primary scenarios have been proposed to explain the presence of the atmosphere:
- Recent impact: A cometary or small icy impactor could have released gases that form a temporary atmosphere. In this scenario, the atmosphere would dissipate within less than 1,000 years unless replenished.
- Cryovolcanic activity: Subsurface ices could be released through cryovolcanic eruptions. The driving mechanism for such activity is currently unknown. If this is the cause, the atmosphere could persist for a longer duration.
"This discovery points to recent activity within the Kuiper Belt." – Dr. Scott Sheppard, Carnegie Institution
Broader Significance
2002 XV93 is the smallest TNO known to have an atmosphere. Previously, only Pluto was considered to retain one among TNOs. Dr. Scott Sheppard of the Carnegie Institution characterized the discovery as evidence of recent activity within the Kuiper Belt.
Future Research
Further observations are required to determine the atmosphere's composition and longevity. The research team has planned additional observations with the James Webb Space Telescope to search for gases such as methane or carbon monoxide.
Monitoring the atmosphere's density over time—specifically, whether it fades (supporting an impact origin) or exhibits seasonal variation (suggesting ongoing internal gas supply)—could help distinguish between the two hypotheses.