Mars exploration. Artwork of astronauts on Mars preparing robotic rovers that will be used to explore and sample the surrounding area. Their manned rover is in the background. The astronauts are part of NASA's Constellation Program, a US space program announced in 2004, which is intended to put astronauts back on the Moon by 2020, followed by missions to Mars, the third planet from the Sun. Mars is a cold, desert world with a thin atmosphere of carbon dioxide. Studies of Martian rocks will reveal their mineral content and provide evidence for theories about Martian geology and water on Mars.