Scientists have discovered a surprising atmosphere around a small object in the outer solar system, challenging our understanding of how these distant bodies retain gases.
A study has found evidence for a thin atmosphere around a small object in the cold reaches of the outer solar system -- but the object is so small that it should not have an atmosphere -- raising questions about when and how it formed.
Thousands of trans-Neptunian objects (TNOs) lie beyond the orbit of Neptune, the most famous one being Pluto. While a thin atmosphere has been observed around Pluto, studies of other TNOs have yielded negative results.
Researchers, including those from the National Astronomical Observatory of Japan, said that most TNOs are so cold, and their surface gravity so weak, that they are not expected to retain atmospheres.
The study, published in the journal Nature Astronomy, took advantage of a lucky "natural experiment" to look for an atmosphere around a TNO known as (612533) 2002 XV93, abbreviated as 2002 XV93.
The trans-Neptunian object has a diameter of 500 kilometres -- that of Pluto is 2,377 kilometres -- and has an orbit such that "it passed directly in front of a star on January 10, 2024", the researchers said.
As the star disappears behind 2002 XV93, it might gradually fade, indicating that the light is being attenuated as it passes through a thin atmosphere -- or it might suddenly wink out as it slips behind the solid surface of the TNO, they said.
Observing the star as 2002 XV93 passed in front of it from multiple sites across Japan, the researchers obtained data consistent with an attenuation by an atmosphere.
Calculations showed that the atmosphere around 2002 XV93 is expected to last under 1000 years, unless replenished, suggesting that it was created or replenished recently.
Further, observations from the US' space agency NASA's James Webb Space Telescope showed no signs of frozen gases on the surface of 2002 XV93 that might sublimate to form an atmosphere.
The researchers said one possibility could be that an event brought frozen or liquid gases from deep inside the TNO to the surface.
Another possibility is that a comet crashed into 2002 XV93, releasing gas that formed a temporary atmosphere, they said.
Further observations are needed to distinguish between these two scenarios, the team said.