Mars is the fourth planet from the Sun, and it is our neighbor in the solar system. People call it "the Red Planet" because its ground is full of iron dust that has rusted, like an old bicycle left in the rain.
Mars is much smaller than Earth, and it is also much colder. On a summer day near its equator, the temperature can reach about 20 degrees Celsius, but at night it can drop to minus 70 or even lower. The air on Mars is very thin, and people cannot breathe it.
Mars is home to Olympus Mons, the biggest volcano in the solar system. It is about two and a half times taller than Mount Everest. Mars also has two small moons, called Phobos and Deimos.
Since the 1960s, many spacecraft have visited Mars. Robots on wheels, called rovers, drive across its surface, take photos and study the rocks. Scientists want to know whether there was ever water — and maybe life — on the Red Planet. One day, perhaps, the first human will walk there.