The first detection of an atmosphere on a trans-Neptunian object beyond Pluto

TL;DR

This paper reports the first detection of an atmosphere around a trans-Neptunian object other than Pluto, revealing that smaller icy bodies can retain atmospheres, challenging previous assumptions.

Contribution

It provides the first evidence that a sub-1000 km TNO can have an atmosphere, expanding understanding of volatile retention in distant icy worlds.

Findings

Detected a thin atmosphere around (612533) 2002 XV93 via stellar occultation.

Surface pressure estimated at 100-200 nanobars, much lower than Pluto's.

Shows that smaller TNOs can retain atmospheres, suggesting ongoing cryovolcanic activity or recent impacts.

Abstract

Trans-Neptunian objects (TNOs) in the outer Solar System are predominantly small, icy worlds long presumed to be atmosphereless except for the largest bodies. Until now, Pluto has been unique among TNOs in exhibiting a substantial atmosphere (nitrogen with trace methane and carbon monoxide) at microbar pressure levels. All other known TNOs, including ~ 1000-km-sized bodies such as Eris, Haumea, Makemake, and Quaoar, have shown no detectable atmospheres in stellar occultation observations, with surface pressure upper limits of order 1-100 nanobars. Here we report the first detection of an atmosphere around a TNO besides Pluto. A stellar occultation by the ~ 250-km-radius plutino (612533) 2002 XV93 on 10 January 2024 revealed a refractive signature, indicating the presence of a thin atmosphere. The derived surface pressure is 100-200 nanobars, i.e. approximately a hundred times lower than Pluto's and yet significantly above previous limits for other larger bodies. This discovery provides the first evidence that even a sub-1000-km TNO can retain an atmosphere, challenging current paradigms of volatile retention. Our findings indicate that a fraction of distant icy minor planets can exhibit atmospheres possibly caused by ongoing cryovolcanic activity or a recent impact event of a small icy object.