tombaugh-regio

Pluto has an atmosphere. In 2015, New Horizons measured its surface pressure at about 1 Pascal — roughly 1/100,000th of Earth's at sea level. That atmosphere is not stable. Over Pluto's 248-year orbit, it inflates and then freezes entirely out onto the surface, cycling between a thin gaseous envelope and nothing at all. We arrived just in time to see it while it still existed.

New Horizons flew within 12,550 km of Pluto on July 14, 2015 — the only spacecraft ever to do so — and transmitted data for 16 months afterward. What it found was not a dead, cratered iceball at the edge of the solar system but an active world with mountains of water ice, a heart-shaped nitrogen glacier the size of Texas, and possibly a liquid ocean beneath the ice.