Thin layers of haze hang above the surface of Pluto in this view from the New Horizons spacecraft. There's evidence that Pluto's thin, cold atmosphere is beginning to freeze onto the surface as the little world moves farther from the Sun. [NASA/JHUAPL]
Pluto may be starting to lose its air. Two recent studies suggest that its atmosphere is either holding steady or getting thinner — a result of colder temperatures as it moves away from the Sun.
Even at its thickest, Pluto’s atmosphere isn’t much — just two hundred-thousandths as thick as Earth’s. The atmosphere forms when Pluto draws close to the Sun. The solar energy heats its surface. That causes frozen nitrogen and other ices to vaporize, forming the atmosphere.
Since 1989, though, Pluto has moved several hundred million miles farther from the Sun. Scientists had expected to see the atmosphere start to freeze out, adding fresh ice to the surface. Instead, though, the atmosphere has gotten denser — roughly doubling in thickness every 10 years.
That trend may be stopping or even reversing. In 2018, scientists measured Pluto’s atmosphere as the little world passed in front of a star. The way the star dimmed revealed the thickness of the atmosphere. The observations showed there was little change since the New Horizons spacecraft flew past Pluto in 2015. If the trend from previous decades had continued, the atmosphere should have been denser.
And in 2019, another team watched as Pluto passed in front of another star. That showed that the atmosphere was about 20 percent thinner than it was three years earlier. The results still need to be verified, though — confirming what’s happening to Pluto’s chilly atmosphere.
Script by Damond Benningfield
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