Pluto’s thin atmosphere is mainly nitrogen, and leaking away from the planet at a significant rate. Scientists speculate that cryovolcanic activity is continually releasing enough new nitrogen vapor to keep the atmosphere from completely dissappearing.
Cryovolcanic. That’s a term you don’t hear every day. Significant areas of Pluto are covered in what looks like glaciers. But they’re not made of ice — ice is too hard to flow at Pluto’s -370F temperature. Instead, the glaciers — which show hints of convection patterns — are likely made of frozen nitrogen:
Cryovolcanism. Just had to say that one more time. You can read more at the New Horizons mission web site.