Mars is the fifth planet from the Sun, and is the second smallest planet in the Solar System.

With a mass of 6.4 x 1023 kg, it is smaller than the planet Mercury. Mars is a terrestrial planet with a thin atmosphere. Temperatures on Mars can drop below -95*C, particularly at high northern latitudes during the winter. Mars is geologically active; surface features have been created by water, ice, wind and dust, and the planet has an ancient and heavily created surface. It is the site of Olympus Mons, the highest known volcano and largest known mountain.

Observational evidence suggests that Mars was subject to liquid water conditions within the last few hundred million years. The conditions may have been as long as two billion years ago. Evidence from the Curiosity rover indicates that the planet's environment billions of years ago may have been more favourable for life, but it was not warm enough to have liquid water on the surface.