Mars exploration, artwork. Astronaut at the rim of Valles Marineris (Mariner Valleys) on Mars. These canyons are many hundreds of kilometres long and are several kilometres deep, dwarfing similar canyons on Earth. Mars is a rocky desert world with no surface water. Its gravity is about one third of that on Earth. The atmosphere is mostly carbon dioxide and surface temperatures are well below freezing. Martian astronauts will have to breathe their own air supply and wear heated spacesuits. Human missions to explore Mars have been planned since the 1950s, usually involving a period of 10 to 30 years to develop the necessary technology and resources.