A small object beyond Pluto could have a thin atmosphere

The possible atmosphere around the 2002 XV₉₃ would be a first for a small object beyond Pluto

A distant icy world appears as a dark disk with a thin glowing halo, with a line of repeated bright points showing a distant star at multiple positions.

A small solar system living further from the sun than Pluto could be enveloped in a thin atmosphere. If confirmed, it would be the first object of its size known to host even a tenuous atmosphere.

“This finding suggests that the small, icy worlds beyond Neptune may not be as dormant or unchanging as we often assume,” says observational astronomer Ko Arimatsu of the National Astronomical Observatory of Japan in Mitaka. “Until now, Pluto was the only trans-Neptunian object with a confirmed atmosphere.” He and his colleagues report observations on May 4 at Natural astronomy.

The team followed the small body – nicknamed 2002 XV₉₃ — using a network of telescopes in Japan. On January 10, 2024, telescopes in three locations recorded it moving in front of a distant star. For other bodies in the solar system, the details of these tiny eclipses, called occultations, have revealed the presence of atmospheres. and even rings.

If 2002 XV₉₃ were naked, the star would have seemed to flash and suddenly reappear. But Arimatsu and his colleagues saw the star’s light fade and gradually recover over about 1.5 seconds. This gentle attenuation is best explained by starlight passing through and being refracted by a thin atmosphere, with a pressure about one ten millionth that of Earth, Arimatsu says.

“I was really surprised,” he said. The object is about 470 kilometers wide, about as wide as the length of the Grand Canyon – so small that its gravity would have to be too weak to hold the gas for long. The atmosphere is expected to dissipate within thousands of years unless something replenishes it, researchers say.

The gas could have been released recently, perhaps by the impact of an icy body like a comet, and astronomers happened to look at just the right time. Or, the body can regularly release gases through icy volcanoes.

An occultation cannot completely rule out other explanations, such as dust, Arimatsu notes. Observations have also not been able to determine what the atmosphere is made of or how high it extends above the body’s surface.

“Future observations will be important,” says Arimatsu. If the atmosphere fades over the next few years, it could mean it was transient and triggered by an impact. If it persists, or varies according to the seasons, this favors the volcano scenario.