A Sharpened Ultraviolet View of Mars

MAVEN's Imaging UltraViolet Spectrograph obtained this image of Mars on July 13, 2016, when the planet appeared nearly full when viewed from the highest altitudes in the MAVEN orbit. The ultraviolet colors of the planet have been rendered in false color, to show what we would see with ultraviolet-sensitive eyes. The ultraviolet (UV) view gives several new perspectives on Mars. Valles Marineris, a two-thousand-mile canyon system, appears prominently across the middle of the image as a blue gash. The deep canyon appears blue due to the scattering of ultraviolet light by the atmosphere, so strong that we cannot make out the bottom of the canyon. The greenish cast of the planet as a whole is a combination of the reflection of the surface plus the atmospheric scattering. The three tall Tharsis volcanoes appear near the left edge, dotted by white clouds forming as the winds flow over them. Bright white polar caps appear at both poles, typical for this season, in which there is a transition from southern-hemisphere winter to summer. The magenta-colored region visible at the south pole shows where ozone is absorbing ultraviolet light — the same property of ozone that protects life on Earth from harmful UV radiation. While ozone tends to be destroyed by chemical processes in the winter on Earth, different atmospheric chemistry at Mars caused it to build up in the winter there. A hint of ozone is also visible near the north pole; more will accumulate there as winter is coming. IUVS obtains images of Mars every orbit when the sunlit portion of the planet is visible from high altitude.