Mars has little more than 10% of the Earth"s mass, and lies 50% further away from the Sun, but the atmospheres on the two planets share some basic similarities. Like Earth, Mars has polar ice caps. There are seasonal variations in its weather, some of them – such as violent dust storms – visible to our instruments on Earth. The presence of ice, formed by the hydrogen and oxygen in Mars" thin atmosphere, shows that the planet once had the right conditions to support microbial life. It"s not proof that Mars had life, but certainly is a clear enough sign that it was possible.