Pluto may have an atmosphere only at certain times of the year. Pluto's orbit is very eccentric. So, Pluto's distance from the Sun varies throughout Pluto's year. Pluto is sometimes nearer the Sun than at other times in its orbit. When Pluto is nearer the Sun, some frozen nitrogen, methane, and carbon monoxide from the surface may change to a gas. This evaporation creates a temporary atmosphere. As Pluto's orbit moves it away from the Sun, these gases may freeze and fall like snow back to the surface. When Pluto is farthest from the Sun, the planet may have almost no atmosphere.
