Tiny world beyond Pluto may have its own atmosphere, study finds

A distant icy object located beyond Pluto may possess a thin atmosphere, making it the smallest and most remote known body in the outer solar system to potentially host a gaseous layer.

The object, known as 2002 XV93, is situated in the region beyond Neptune and has drawn the attention of astronomers after recent observations suggested the presence of an atmosphere. Until now, Pluto was the only trans-Neptunian object confirmed to have one.

A research team led by astronomer Ko Arimatsu of the National Astronomical Observatory of Japan made the discovery while monitoring the object with a network of telescopes. On January 10, 2024, 2002 XV93 passed in front of a distant star, an event known as a stellar occultation. Such events allow scientists to study distant objects by analyzing how they affect the starlight passing behind them.

Instead of the star disappearing and reappearing abruptly, researchers observed its brightness fading and returning gradually over approximately 1.5 seconds. This behavior suggests that the starlight passed through a thin layer surrounding the object, possibly an atmosphere. Scientists estimate that if an atmosphere exists, its pressure is roughly one ten-millionth of Earth's atmospheric pressure.

The finding surprised researchers because 2002 XV93 is only about 470 kilometers wide. Objects of this size are generally believed to have insufficient gravity to retain gases for extended periods, raising questions about how such an atmosphere could still exist.

Scientists propose several possibilities. A recent collision with a comet-like body may have released gas into the surrounding space, temporarily creating an atmosphere. Another theory suggests that the object could be experiencing cryovolcanic activity, where icy materials erupt from beneath the surface and release gases.

However, many uncertainties remain. The observations cannot determine the exact composition of the surrounding material, meaning it could consist of dust rather than gas. Researchers also lack information about the atmosphere's height and structure.

Future observations will be crucial in understanding the phenomenon. If the atmosphere gradually disappears, it may indicate a temporary cloud created by an impact event. If it persists or changes over time, it could point to ongoing geological activity on the distant world.