Mars. Panoramic illustration of the surface of the planet Mars. Mars is an arid, rocky planet, its surface and atmosphere coloured red by rocks and dust rich in iron. Faint clouds sometimes form in the atmosphere from the trace of water vapour present. On the left is a volcano and on the right a dried riverbed - evidence that water once flowed on the Martian surface. The bright star on the right is the Sun. Also visible are Mars's two moons, Phobos (left) and Deimos.