If Pluto Keeps Spewing Nitrogen, Why Is It Still Full of It?

Something mysterious is happening on the surface of Pluto: No matter how much nitrogen the atmosphere releases into space, it's still chock-full of the stuff. New work examines the possible culprits for the stealthy nitrogen resupply, hinting at active geologic activity inside the dwarf planet. Pluto's atmosphere has 10,000 times lower pressure than Earth's at the surface, and hundreds of tons of nitrogen are escaping every hour.