The most detailed global view of Mars ever obtained from Earth was taken by the Wide Field Planetary Camera-2 aboard the Hubble Space Telescope (HST) on 10 March 1997, just before Mars opposition, when the planet made one of its closest approaches (about 100 million km). Mars has rotated about 90deg between each image. The specific bands were chosen to discriminate between airborne dust, ice clouds and prominent surface features. The colour picture was created by combining images taken in blue (433 nm), green (554 nm) and red (763nm) filters. They show Mars during the transition between spring and summer in the northern hemisphere (just before summer solstice). The annual north polar carbon dioxide frost (dry ice) cap is rapidly sublimating, revealing the much smaller permanent water ice cap. This polar cap remnant, along with a few nearby detached regions of surface frost, is most obvious in pictures taken through UV, blue and green filters. These filters also show numerous bright water ice clouds. The brightest clouds are in the vicinity of the giant volcanoes on the Tharsis Plateau (right of centre on left image), and in the giant impact basin, Hellas (near bottom of right image), but a diffuse haze
covers much of the Martian tropics as well. The familiar bright and dark
markings on the Martian surface are most obvious on the images taken through red and near-IR filters. These images clearly reveal the large, dark, circular 'sea' of sand dunes (Olympia Planitia) that surround the north pole,as well a number of other familiar features, including the giant Tharsis volcanoes. The 27 km high Olympus Mons is near the centre of the left-hand image, with Arsia, Povonis and Ascraeus Mons forming a south-west to north-east line just to its right. [Image Date: 20-03-97] [97.04.002-002]