How Big is Pluto's Atmosphere?

Explanation: Earth's atmosphere has an equivalent thickness – the thickness if you compress the atmosphere to uniform pressure and density – of about 10 kilometers, or six miles. Compare this with the radius of Earth, 6,370 kilometers, and you see that the razor-thin thickness of Earth's atmosphere is about 0.17% of its radius. Pluto's atmosphere has a near-surface equivalent thickness of about 40 kilometers, which is almost 4% of its 1,200- kilometer (or so) radius. But the 'outer limit' of Pluto's atmosphere is very difficult to define, although we know that it is very far from the surface. If one defines it similar to the way we define the exobase of Earth’s atmosphere, then Pluto’s atmosphere has an outer limit of at least seven times Pluto’s radius above it surface. This means that the volume of Pluto's atmosphere is over 350 times the volume of Pluto itself!


Image credit: JHUAPL.