Box 2: Rocks relating to Earth, Moon and Mars
The Moon's pockmarked face tells a story of meteorite impacts through the ages. It is studded with half a million craters larger than a kilometre across. The surface of the Moon is covered with dusty, pulverised rock which was broken up in these impacts.
Mars is a rocky, red planet, whose colour is due to iron oxide (rust) in its soil. Much of its surface is a freezing desert, covered with rock-strewn dunes. Like the Moon, it is home to thousands of impact craters but its huge volcanoes and vast canyons are unique, the largest discovered in the solar system.
The Earth is the only planet in the Solar system where the temperature and atmospheric pressure allow liquid water to exist at the surface. It is also, as far as we know, the only planet which has life. Water and life, as well as impacts, volcanism, and earthquakes, have sculpted the surface of the Earth into its familiar landforms.