Summer on Pluto - Artist view
author: Walter B. Myers/Novapix
reference: a-plu99-00017
Image Size 300 DPI: 27 * 20 cm
Despite its small size and extreme distance from the Sun, Pluto does have an atmosphere. The atmosphere arises because there are periods when Pluto is closer to the Sun than Neptune, making it the 8th planet from the Sun for roughly 20 years at a time (on 11 February 1999, Pluto crossed Neptune's orbit and once again became farther from the Sun than Neptune and will remain so until the year 2231).
During this plutonian "summer" the ices on Pluto's surface sublimate and form a methane and nitrogen atmosphere. This atmosphere is continually produced and lost again while Pluto is inside Neptune's orbit; during this time the density of Pluto's atmosphere may rival that of Mars.