AP Photo

Maybe because it appears as a speck of blood in the sky, the planet Mars was named after the Roman god of war. From the point of view of life as we know it, that's appropriate. The Martian surface is incredibly hostile for life. The Red Planet's thin atmosphere does little to shield the ground against radiation from the Sun and space. Harsh chemicals, like hydrogen peroxide, permeate the soil. Liquid water, a necessity for life, can't exist for very long here—any that does not quickly evaporate in the diffuse air will soon freeze out in subzero temperatures common over much of the planet.