Geology/Atmosphere

Over 98% of Pluto's surface consists of solid nitrogen, with traces of methane and carbon monoxide. The face of Pluto pointed toward Charon, its largest moon, contains more solid methane, whereas the opposite face contains more nitrogen and solid carbon monoxide. On average, the temperature on Pluto is -387°F, making it too cold to sustain life.

Pluto has a thin, atmosphere that expands when it comes closer to the sun and collapses as it moves farther away—similar to a comet. The main constituent is molecular nitrogen, though molecules of methane and carbon monoxide have also been detected.

When Pluto is close to the sun, its surface ices sublimate (changing directly from solid to gas) and rise, temporarily forming a thin atmosphere.

Pluto's low gravity (about six percent of Earth's) causes the atmosphere to be much more extended in altitude than our planet's atmosphere. 

When Pluto is the furthest from the sun, it becomes much colder. During this time, the bulk of the planet's atmosphere may freeze and fall as snow to the surface.