Mars is the fourth planet from the Sun and is named after the Roman God of war. The planet is a distinctive shade of red and is the last of the rocky terrestrial planets. Mars is substantially smaller than Earth and Venus but larger than Mercury. The planet has been the subject of intense speculation about the existence of extra terrestrial life with evidence of water on the surface at the polar ice caps. While recent robotic explorations have shown that the presence of life is unlikely it has still not been conclusively ruled out.
Mars has a thin atmosphere, much thinner than Earth's. It is kept this way by the solar winds stripping atoms from the top layer, Mars's atmosphere lacks a magnetosphere to protect it. The surface pressure of the Martian atmosphere is less than one percent of that found on Earth. Despite the sparseness of the atmosphere however, it extends 5km higher than Earth's due to lower gravity. Mars has a relatively low mass and the surface gravity is just 38 percent of Earth's.
Mars is home to the largest mountain in the Solar System, Olympus Mons. It is three times higher than Mount Everest and the result of substantial volcanic activity with shallow slopes covering a massive area. Mars is also home to many other interesting geographical features such as canyons and valleys. Many of these features are attributed to running water, although it has been proved to no longer exist it is thought that at one time Mars may have had rivers on its surface. The Phoenix lander has found ice under the surface of the planet and Mars is the most water-rich location outside Earth that we have found so far.
Mars has two small moons, Phobos and Demios, both with irregular shapes. They are thought to be captured asteroids and the orbit extremely close to the planet. It is not fully understood how the moons have come to orbit Mars, however it is believed that Phobos is a relatively recent capture as it follows an unstable orbit and will collide with the Red Planet in around 50 million years.
Mars has been extensively explored by robotic spacecraft and probes by the USA, Russia, Europe and Japan. Probes began exploring Mars even before Man had landed on the Moon with the first flyby occurring in 1964. The Soviet were the first to successfully land objects on the planet, but they lost contact soon after arrival. In 1976 the NASA probes Viking 1 and 2 made it to the surface of Mars, spending several years there. They provided many images and helped to map the surface. The most recent probe to land on Mars is the Phoenix Lander. It arrived in May 2008 and began investigating the Martian soil, finding conclusive evidence of water ice. Phoenix landed much closer to the pole than any other spacecraft.
There are many future missions planned to Mars and in 2004 President George W. Bush announced that NASA's vision for space exploration would be to launch a manned mission to the planet. NASA administrators believe that they will have successfully landed a man on Mars by 2037. Mars has been the subject of serious talk of eventual colonisation, as it is seen as the most suitable for life and the most habitable environment in the Solar System outside Earth. Mars has many of the elements needed for life present in its soil and with a carbon dioxide-rich atmosphere it is thought that with some terraforming that algae may be able to survive at the poles. Terraforming Mars is an area that is being looked into as a future destination for civilisation once the increasing heat of the Sun makes Earth uninhabitable.
Mars is a charismatic planet, inspiring countless works of fiction and a massive amount of speculation about the secrets it may hold. It has been a characteristic of our space exploration that many of the early romantic ideas of conditions on the surface have been dispelled and the planet has been found to be lifeless and largely barren. Martian thinking is now turning towards finding out its past and planning for its future.