Utopia Planitia is a smooth plain on Mars situated northwest of the Elysium Planitia volcanoes and chosen as the landing site for Viking 2 in 1976. The image here, taken by Viking 2 Lander camera 2 on 18 May 1979, shows a thin layer of water ice frost on Utopia Planitia. The layer is thought to be only about two thousandths of a cm thick. It is speculated that dust particles in the atmosphere pick up tiny bits of water. When it gets cold enough for carbon dioxide to solidify, some of it attaches to the dust and ice and it falls to the surface. The view is looking towards the south southeast; the long boulder to the right is roughly one meter across.