TUCSON, USA, July 31, 2026 - Pluto's atmosphere may be beginning to freeze out as the dwarf planet travels away from the Sun, according to a team led by Amanda Sickafoose of the Planetary Science Institute. The team found that Pluto's atmospheric pressure stayed constant from 2015 to mid-2021, then dropped 16% between mid-2021 and July 2023. The drop was measured in the lower atmosphere.

The findings were published in the Planetary Science Journal. To track the atmosphere, the scientists used stellar occultations, the moments when Pluto passes in front of a distant star. They observed 10 occultations starting in 2017, though only four of them were seen from more than one location on Earth.

The research suggests Pluto's atmosphere may be starting to collapse. Astronomers first detected that atmosphere in 1988, and NASA's New Horizons spacecraft flew past Pluto in 2015. Pluto's air is mostly nitrogen, with methane and carbon monoxide.

The dwarf planet is still moving away from the Sun and will not stop doing so until 2114. It takes 248 years to complete one orbit. The next good opportunity to observe a Pluto occultation comes in 2027.

Space Nugget. On small, icy worlds far from the Sun, an atmosphere can be fed by surface ice turning into gas. As such a world drifts farther out and its surface cools, more of that gas freezes back onto the ground as frost, and the atmosphere thins. A stellar occultation lets astronomers weigh a distant atmosphere from Earth: as a world slides in front of a star, the way the starlight fades and returns reveals how dense the gas is at different heights.