Mars. Composite satellite image of the surface of Mars, showing the north polar cap (white), a mixture of ice and dust that extends to the 80 degree latitude circle. Mars' northern hemisphere is characterised by vast, sparsely cratered plains with high volcanoes. Its southern hemisphere is highly cratered and features large canyon systems such as Valles Marineris, which is 4000 kilometres in length (seen here at bottom). This image was created using data from the Mars Global Surveyor spacecraft's Mars Orbiter Laser Altimeter.