Pluto’s atmosphere, composed mainly of nitrogen with traces of methane, carbon monoxide, and hydrocarbons, is beginning to thin as the dwarf planet enters the coldest phase of its 248-year orbit around the Sun. This observation follows recent findings indicating a drop in atmospheric pressure, suggesting that the atmosphere may be collapsing ahead of a long Plutonian winter.
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Astrophysicists have noted that atmospheric changes on Pluto follow the planet’s seasonal cycles, which occur over decades due to its unique orbit. Since its discovery in 1930, Pluto's atmosphere was first detected in 1988 through a method called stellar occultation, where the planet temporarily obscures starlight. Detailed observations were later conducted by NASA’s New Horizons spacecraft during its flyby in 2015, revealing Pluto’s complex atmospheric characteristics.
Amanda Sickafoose, a planetary scientist at the Planetary Science Institute and lead author of a recent study published in The Planetary Science Journal, explained that stellar occultations provide crucial data about the composition, temperature, and pressure of Pluto’s atmosphere. However, these events are rare, happening only once or twice a year, which poses challenges in collecting comprehensive data over time.
Sickafoose and her team compiled a broad dataset of Pluto’s atmospheric observations from 1988 to 2023, including ten new data points from 2017 to 2023, taken from over 15 telescope locations worldwide. Their analysis revealed that while Pluto’s atmosphere remained relatively stable post-New Horizons through 2021, a 16% decrease in pressure was observed in the lower atmosphere in 2022 and 2023. This cooling trend is likely causing haze particles to fall as nitrogen snow.
Perianne Johnson, a Pluto climate scientist at Purdue University, remarked on the significance of these findings, emphasizing the reliability of the reported changes in atmospheric pressure. She noted that while a 16% drop might appear minor, it reflects a rapid change within a brief period, highlighting that atmospheric collapse might indeed be beginning.
Scientists project the atmospheric pressure on Pluto will continue to decline for over 150 years before recovering around the 23rd century. Understanding this process could provide insights into where atmospheric nitrogen condenses and falls as snow, particularly in Pluto’s southern ice deposits. The next chance for detailed observations will occur in 2027, which may help confirm the current trends in Pluto's atmosphere.