Geology/Atmosphere

More than 98 percent of Pluto's surface consists of solid nitrogen, with traces of methane and carbon monoxide. The face of Pluto oriented toward Charon contains more solid methane, whereas the opposite face contains more nitrogen and solid carbon monoxide. The temperature on Pluto can be as cold as -375 to -400 degrees Fahrenheit (-226 to -240 degrees Celsius).

Pluto has a thin, tenuous 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 to temporarily form 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.

Pluto becomes much colder during the part of each year when it is traveling far away from the sun. During this time, the bulk of the planet's atmosphere may freeze and fall as snow to the surface.