THE HUBBLE SPACE telescope has returned the clearest image of Mars taken from the Earth's vicinity, 103 million kilometres away. Most of the carbon-dioxide frost around the permanent water-ice polar cap on Mars' springtime northern hemisphere has sublimated and wispy white clouds indicate that the atmosphere is cooler than when the planet was explored by the Viking probes in 1976. Morning clouds, on the western (left) limb, form overnight when the temperatures plunge and water in the atmosphere freezes into ice crystals. The volcano Ascraeus Mons pokes above the cloud deck, 25km above the surrounding plains near the western terminator. In the lower left is the Valles Marineris, an immense rift valley the length of the continental USA, and near the centre is the Chryse basin. The Agrgyre impact basin, at the bottom, appears white because of clouds or frost. Seasonal winds carry dust to form striking linear features reminiscent of the legendary Martian "canals". The dark areas, once misinterpreted as regions of vegetation, are areas of coarse sand which is less reflective.
Source: Flight International