Pluto's atmosphere may be in the process of disappearing as the dwarf planet continues its slow trajectory toward colder and more distant regions of the Solar System. A new investigation detected the first indicators of a notable drop in atmospheric pressure, suggesting that the gases surrounding the celestial body may be freezing onto its surface.
This research was conducted by scientists led by Amanda Sickafoose of the Planetary Science Institute and was published in the Planetary Science Journal.
Pluto is moving further and further away from the Sun
Pluto orbits the Sun in a highly elliptical trajectory. It will continue to move away from the star until 2114, reaching even colder areas before beginning its return. Researchers indicate that this is Pluto's first movement toward these outer zones since its initial discovery in 1930.
With the reduction in temperatures, the dwarf planet's atmosphere has the potential to progressively freeze and deposit on the surface as ice.
First signs of change
The team analyzed records collected between 2017 and 2023 to monitor Pluto's atmospheric evolution. The data revealed that, during the period between the New Horizons probe's passage in 2015 and part of 2021, the atmospheric pressure remained relatively stable.
However, between mid-2021 and July 2023, scientists recorded a decrease of about 16% in atmospheric pressure. The models used in the study assume a haze-rich atmosphere, similar to that observed by New Horizons during its approach flight. The authors interpret this drop as possible early signs of an atmospheric collapse process.
How scientists study such a distant atmosphere
Currently, no spacecraft is close enough to Pluto to monitor its atmosphere directly. Furthermore, even the most sophisticated telescopes view the dwarf planet only as a small luminous point.
To overcome this limitation, researchers use a method known as occultation. In these events, Pluto aligns perfectly in front of a star viewed from Earth. As the star disappears behind the dwarf planet, its light passes through Pluto's atmosphere before being obscured. By precisely measuring how this brightness decays and returns, scientists can determine atmospheric characteristics, such as its density and pressure.
Since 2017, the team has tracked ten stellar occultations. In four of these occurrences, the same event was simultaneously recorded by different observatories, allowing for the comparison of measurements and the analysis of different parts of the atmosphere. Sickafoose commented: 'I am constantly impressed by the fact that the simple technique of observing a star dim and reappear allows us to study an extremely thin atmosphere—with only a few millionths of the density of Earth's atmosphere—on a world about two-thirds the size of our Moon and located 30 times farther from the Sun.'
Atmosphere and surface are directly linked
The composition of Pluto's atmosphere primarily includes nitrogen, along with methane and carbon monoxide. These elements can generate a haze that surrounds the dwarf planet. Researchers point out that as atmospheric pressure drops, this haze tends to become less dense and concentrate at lower altitudes.
Scientists emphasize that the behavior of the atmosphere is intrinsically linked to the ice present on Pluto's surface, although many aspects of this interaction are not yet fully understood.
Observations will continue in the coming decades
For the authors, many years of additional observations will be necessary to definitively confirm whether Pluto's atmosphere has begun a permanent collapse process. Sickafoose concluded: 'We are at a particularly interesting time for Pluto. Our work suggests that the atmosphere recently began losing pressure. I hope we can obtain more data in the coming years and decades to confirm or refute this trend.'
