The discovery of a strange atmosphere on a small icy world beyond Pluto has sparked excitement and intrigue in the scientific community. This finding challenges our understanding of the outer Solar System and raises questions about the nature of these distant celestial bodies. The object in question, 2002 XV93, is a trans-Neptunian object with a size of only about 500 kilometers, much smaller than Pluto. Its weak gravity and the deep cold of its orbit suggest that it should not be able to retain an atmosphere, as the gases would escape too quickly. However, observations made during a stellar occultation event in January 2024 revealed a gradual fading of starlight as 2002 XV93 passed in front of a distant star, indicating the presence of a thin atmosphere. This discovery is particularly fascinating because it challenges the conventional understanding of the outer Solar System, where small icy bodies are expected to be devoid of atmospheres due to their weak gravity and the presence of only volatile ices like methane, nitrogen, and carbon monoxide. The atmospheric modeling suggests that the surface pressures required to explain the observed light curves are remarkably low, about 50 to 100 times lower than Pluto's present surface pressure. This implies that the atmosphere is likely to be short-lived, surviving only about 100 to 1,000 years unless replenished. The research points to two main possibilities for the origin of the atmosphere: outgassing tied to cryovolcanic activity or a recent impact. Cryovolcanic activity, while possible, seems unlikely for a small object like 2002 XV93, which should have a thick, cold outer shell. On the other hand, a recent impact could release gas directly from the impactor or excavate buried volatiles from below the surface. However, the chance of such an impact occurring over 100 years is extremely low, making it a challenging explanation. The discovery of this atmosphere has significant implications for our understanding of the outer Solar System. It suggests that some smaller icy bodies may briefly acquire atmospheres through interior activity or chance collisions, then lose them on timescales short enough to make them hard to catch. This highlights the importance of repeat observations and the potential for smaller telescopes and citizen astronomers to contribute to future monitoring efforts. The research findings have been published in the journal Nature Astronomy, and they open up new avenues for exploration and understanding of the complex dynamics in the outer reaches of our solar system.
