We got to Pluto just in time: Its air is starting to freeze out

The New Horizons mission to the outer solar system flew past Pluto in July 2015, skimming over its surface by just 12,500 kilometers after a journey of 5 billion kilometers and returning incredible images and data of the tiny, icy world.

The mission was conceived, designed, built, and launched in record time because scientists wanted to get to Pluto as rapidly as possible. Why? Because Pluto orbits the Sun on a decently elliptical path, and around the year 1989 it was its closest point to the S...