• Discovered: Prehistoric times
• Diameter: 6,787 km
• Temperature on surface: Between -133°C and 20°C
• Distance from the Sun: Varies between 206 and 249 million km
• Satellites: 2, Phobos and Deimos

Galileo was the first person to observe the planet through a telescope in the early 1600s. Its distinctive colour, associated by the Romans with blood, makes Mars a highly visible planet in the night sky and it can be seen with the naked eye. Mars’ orbit is closest to the Earth every 26 months.

Although relatively small – its radius is about half that of the Earth’s – Mars boasts scenery on a massive scale.

Its surface has been pummelled by asteroids and, running roughly along part of the equator, is an enormous set of canyons called the Valles Marineris. This split in the Martian crust is around 4,000 km long, up to 600 km wide and 7 km deep in places.

Mars also has the highest volcano in the solar system. Olympus Mons stands at 26 km above the surrounding plain, three times higher than Mount Everest.

The Martian environment is far from hospitable. The thin atmosphere is made up mostly of carbon dioxide with extremely low levels of oxygen.

Temperatures can drop to -133ºC although in the Martian summer it’s more typically around 0ºC. The surface can be extremely stormy with winds reaching speeds of up to 100 km per hour and there are frozen water ice caps at the poles.

There is no definitive evidence that life exists or existed on Mars – yet – but many scientists believe that microscopic life may have existed there at some point in the past. These questions could be answered by the future ExoMars mission.

Mars Express is operated by the European Space Agency (ESA) with significant UK involvement in its design, operation and science.

Since arriving at the Red Planet in December 2003, the ESA mission has sent back scientific data of unprecedented quality. Instruments are searching for water and measuring climate, volcanic, magnetic and geological activity.

Mars Express has found evidence of glacial and volcanic activity in the relatively recent past. There has also been a tentative detection of tiny amounts of methane in the atmosphere. As the methane could only exist on Mars for a few hundred years before being broken down by radiation, its presence can only be explained if there is some process, perhaps biological, keeping it replenished.

UK scientists have been at the forefront of efforts to investigate the interaction between the planet and the solar wind – the stream of charged particles coming from the Sun. These particles are eroding the Martian atmosphere and could be responsible for stripping away a large amount of the water that was once believed present.

Auroras – patterns of coloured light in the atmosphere - have also been discovered in the Martian sky but because Mars doesn’t have a magnetic field, researchers have concluded that the auroras are created as a result of local magnetic fields generated in the planet’s crust making them unique in the Solar System.

The Mars Express mission was due to end in October 2007 but has been extended until 2009.