New Horizons captured this image of Pluto on July 15. Backlit by the Sun, the dwarf planet is dark, while its atmosphere resembles a bright halo. Mission scientists think the atmosphere may help explain the appearance of Pluto’s surface.
Within the atmosphere are two distinct layers of haze, one about 80 kilometers (50 miles) above the surface and the other at an altitude of about 50 kilometers (30 miles). Scientists believe the hazes form when ultraviolet sunlight breaks up methane gas particles, triggering the buildup of more complex hydrocarbon gases. As these hydrocarbons drift to the lower, colder parts of the atmosphere, they condense into ice particles that create the hazes. The ultraviolet sunlight then chemically converts the hazes into the dark hydrocarbons that color Pluto’s surface.
Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute