Mars is the fourth planet from the Sun. It is about 1.5 times as far from the Sun as Earth is. Mars looks red. There is rusty iron in its ground. A day on Mars lasts about 24.6 hours. That is a little longer than a day on Earth.

Mars is a cold, dry, desert world. Temperatures on Mars can drop to about minus 153 degrees Celsius. They can reach about 20 degrees Celsius on a warm day. Today, water on Mars is found mostly as ice. It is near the poles. Long ago, liquid water was on the surface of Mars.

The air on Mars is thin. It is mostly carbon dioxide. People cannot breathe the air on Mars. Gravity on Mars is weaker than on Earth. It is only about 38 percent as strong. So you would weigh much less there.

Mars has two small moons. They are named Phobos and Deimos. They are lumpy, like potatoes. They are not round like our Moon. Phobos circles Mars about three times every Mars day. That takes under 8 hours. Asaph Hall found the two moons in 1877.

Mars is about 6,780 kilometers (4,212 miles) across. That is about half the width of Earth. Olympus Mons is on Mars. It is the biggest volcano in the Solar System. Valles Marineris is on Mars too. It is the biggest canyon in the Solar System.

In 1997 the Mars Pathfinder lander carried Sojourner. It was the first robot rover to drive on Mars. Curiosity is a robot rover about the size of a small car. It studies rocks, soil and air. A small helicopter named Ingenuity was the first aircraft to fly on another planet. It flew on Mars.

Words to know

• rover: a robot car
• lander: a landing craft
• lumpy: not round
• moons: space rocks