Pluto's hazy atmosphere may be collapsing as it moves farther from the sun

Pluto is on an icy march away from the sun. In 2114, it will turn back, but until then, its elliptical orbit will carry it to colder and darker parts of the outer solar system. This is Pluto's first time entering the outer ...

Details of atmospheric changes during this journey have been observed by a team of researchers led by Planetary Science Institute senior scientist Amanda Sickafoose, and they may have even detected the first signs of Pluto's atmospheric collapse. In a new paper published in the Planetary Science Journal , Sickafoose and her team describe how Pluto's atmosphere changed over the 2017–2023 period. They found that between the 2015 New Horizons flyby and partway through 2021, Pluto's atmospheric pressure remained constant. Then, between mid-2021 and July 2023, the bulk pressure decreased by 16%. Their models assumed a hazy atmosphere, as was seen during the Pluto flyby.

Reading Pluto by starlight There are no spacecraft near enough to Pluto to see its atmosphere, and from Earth, Pluto appears to be nothing more than a tiny blob, even to the best space telescopes. Luckily, as Pluto, Earth and even the stars slowly move through the sky, chance alignments, called occultations, cause Pluto to pass in front of some stars. By observing how starlight changes as a star passes behind Pluto during such occultations, scientists can characterize Pluto's atmosphere.

Pluto’s haze layers as observed by the New Horizons spacecraft in 2016. Credit: NASA/JHUAPL/SwRI Read more

These maps show example paths of Pluto’s occultation shadows. Only four of the 10 occultations could be observed from multiple locations on Earth for this paper. The solid lines indicate the top, middle and bottom of Pluto’s shadow on each date, and the arrows near the bottom of the image show the direction of motion of the shadow. White text indicates the locations of the successful observing stations. The black dots are the closest approaches of Pluto to the Earth in the centers of the shadow paths. Credit: A. Sickafoose Read more

Light curve from the 2026 June 1 occultation, observed from Savannah Skies Observatory in Chillagoe, Queensland, Australia. The gray vertical lines indicate different stages of the occultation. The baseline flux level contains combined light from the star and the Pluto system (Pluto plus all of its moons). The flux drops gradually as the starlight bends and scatters in Pluto’s atmosphere, reaching nearly zero flux as defined by only light coming from the Pluto system. As the star appears on the other side of Pluto, the light gradually reappears in the atmosphere before returning to full strength. Credit: A. Sickafoose Read more