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Diameter6794 km, 0.53 x Earth's
Mass0.11 ME
Volume0.15 VE
Average Distance from Sun228 x 106km = 1.523 AU
ColourOrangey red
TemperatureDay: 22°C
Night: -120°C
AtmosphereVery thin carbon dioxide
Length of Day1.02 days
Length of Year687 days
No. of MoonsTwo
Gravity0.38 x Earth's

Mars is the fourth planet from the Sun. It is the most likely place in the Solar System to find alien life. If life is found there it won't be little green men, but very tiny bacteria.

The Sojourner Rover from the Pathfinder mission Today Mars is very cold and only has a tiny amount of water, but scientists think that it was much warmer and wetter in the past. There is no flowing water on the surface in rivers or lakes. All of the water is trapped underground in rocks or in the ice caps at the north and south poles. The NASA spacecraft Pathfinder which landed on Mars also took pictures of a thin icy dew in the mornings.

Mars has seasons like Earth, but because the year is twice as long, the seasons also last twice as long.

The surface of Mars is rocky, with craters and huge canyons across it. It is called the Red Planet because of the colour of the dust. This is an orangey-red colour because it contains a lot of oxidised iron (rust).

Some of the canyons were that we see on the surface were created by water that flowed across the planet thousands of years ago, and some were formed by the surface cracking. The largest is called Vallis Marineris, which stretches for about 4000km, or about the same distance as the width of the United States. It is so deep that if you dropped Mount Everest inside it, the mountain would just peek above the top. There are also ice caps at both the North and South poles, made of water ice and carbon dioxide ice. These grow in the winter as it gets colder and shrink in the summer as it gets warmer and the ice melts.

Vallis Marineris

Mars has the highest volcano in the Solar system, called Olympus Mons. It is three times the height of Everest. Olympus Mons can only exist on Mars because the planet has a very low gravity. If the volcano was picked up and put on Earth it would collapse under its own weight.

The largest crater on the surface is called Hellas Crater, caused by a meteorite hitting the planet. The impact that caused it was so huge that it sent shockwaves around the planet and made a massive area of volcanoes on the other side called the Tharsis Mons.

Phobos (right) and Deimos (left) compared with the asteroid, Gaspra (top) Mars has two moons, called Phobos and Deimos. These are both are thought to be asteroids which moved too close to the planet and were captured by its gravity.

Phobos is the largest of the two and orbits very close to the planet. It goes round once every 7 hours, so if you were stood on the surface looking up, Phobos would go across the sky about three times a day. There is a huge crater on the moon called Stickney crater. This stretches about half way along the surface. The collision that created it was so hard that Phobos might break up into a ring around Mars in the next few million years.

Deimos is the smaller moon and orbits much further away. The surface of the moon is very smooth because it is covered in a fine dust called "regolith". This was thrown up by many collisions before settling down to fill in the deepest craters. Deimos spins once in the same time it takes to go around Mars, so the same side is always facing the planet

A new mission to Mars is planned for launch in 2003, called the Mars Express. This will carry the Beagle 2 lander, which will search for signs of life on the planet. Beagle 2 is a European Space Agency (ESA) mission, which is partly being built here in the UK.

The Beagle 2 lander as it would look on the surface of Mars
All Rights Reserved Beagle 2

Planets Introduction




The Moon









Extra-Solar Planets

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Authors: Carolyn Brinkworth and Claire Thomas

Last updated: July 2001