Pluto's atmosphere is collapsing as it drifts away from the sun into a deep freeze
As Pluto edges further away from the sun, the chilly temperatures are causing its atmosphere to condense onto its barren surface as frost.
Pluto's atmosphere is believed to be weakening as the dwarf planet moves farther away from the sun, according to recent observations made by astronomers. Pluto's surface temperature is around -382 degrees Fahrenheit (-230 degrees Celsius), while its upper atmosphere is slightly warmer at -333 degrees Fahrenheit (-203 degrees Celsius).
As Pluto drifts away from the sun, its nitrogen-rich atmosphere is expected to collapse and freeze, forming frost on the cold surface. A team led by Amanda Sickafoose from the Planetary Science Institute at Arizona State University claims they have observed the beginning of this process.
The team noticed that Pluto's atmosphere pressure has recently started decreasing. Pluto's orbit is highly elliptical and tilted at a steep angle, causing it to move away from the sun after its closest approach to the sun in 1989. Since then, Pluto has been moving away from the sun, and it should reach its farthest point from the sun, called aphelion, in 2114. At that point, Pluto will be about 49 astronomical units (7.3 billion kilometers/4.6 billion miles) away from the sun.
NASA's New Horizons mission, which flew past Pluto in July 2015, measured the dwarf planet's atmospheric pressure to be 10 microbars. This is a very small amount, millions of times lower than Earth's atmospheric pressure. New Horizons provided the first look at Pluto's atmosphere in infrared wavelengths during its flyby.
Since NASA's mission, astronomers have relied on more indirect methods to monitor Pluto's atmosphere. One such method is observing stellar occultations, where Pluto passes in front of a distant star. When an atmosphere exists, the starlight doesn't disappear all at once, but rather fades gradually as the atmosphere scatters and refracts the starlight before the star disappears behind Pluto's solid body.
Between 2017 and 2023, Sickafoose's team observed Pluto's atmosphere during ten stellar occultations, which helped them determine the pressure drop in Pluto's atmosphere.
Previous research suggested that Pluto's atmosphere began freezing out in 2018, but Sickafoose's team found that the atmosphere remained constant between 2015 and mid-2021. However, between mid-2021 and the last occultation they observed in 2023, Pluto's atmospheric pressure dropped by 16 percent. This pressure drop was deduced from the light curves, which show how the star's brightness changed during an occultation.
The team interprets this as haze particles settling towards lower latitudes, which is what is expected when the atmospheric pressure decreases.
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