The Hubble Space Telescope (HST) returned many very useful images even before the dramatic repair mission NASA astronauts performed in December 1993. This HST image (following the repair) shows both dark and light regions on the martian surface; both regions are actually different hues of pale pink-red, but here the colors have been enhanced by computer processing to aid in seeing subtle variations. Mars has an atmosphere with a density of <1% that of Earth, but still sufficiently dense to produce a distinct blue haze visible along the upper (northern) limb. The atmosphere on Mars consists almost entirely of carbon dioxide, and temperatures get sufficiently low to freeze out some of the atmosphere as solid carbon dioxide (“dry ice”), visible as white along the top limb.
Hubble Space Telescope image (Press Release PRC-95-17B).