FACT ONE Of all the planets in the Solar System, Mars is the one that people believe is most likely to contain or to have contained life. In 1900, a prize was offered to the first person to be contact an extra-terrestrial being. However, this extra-terrestrial being was not allowed to come from Mars because that would make the competition too easy! In 1938, a radio broadcast of The War of the Worlds by H.G. Wells (a story about an invasion of Earth by Martians) caused a near panic in America because so many people believed it to be true. FACT TWO The largest volcano in the Solar System is on Mars. It is called Olympus Mons. FACT THREE Mars has polar caps like Earth, although Mars' polar caps contain mostly frozen carbon dioxide instead of frozen water. FACT FOUR Mars is believed to have had water flowing around it like Earth once. It may have had a blue sky too. However, it is unlikely that it had grass, trees and plants like Earth has now. FACT FIVE The Valles Marineris, the greatest gorge on any planet in the Solar System, was caused when volcanoes erupting around it tore up the land, leaving a huge valley. FACT SIX We can see how long Mars has been a 'dead' planet by the number of meteorite impacts on its surface. In comparison, Earth and Venus have fewer impact craters because they have newer surfaces formed by recent geological activity. FACT SEVEN Mars has seasons like Earth. This is caused by the tilt of the planet's axis, at a similar angle to the tilt of Earth's axis. FACT EIGHT The Sun appears about half the size on Mars as it does from Earth. FACT NINE The first space probe to take pictures of Mars' surface (Mariner 4 in 1964) is still in space although inactive, orbiting the Sun. Still orbiting Mars itself are Mariner 9 (launched in 1971, now in active), Viking 1 and 2 (launched in 1975, now inactive), the Mars Global Surveyor (launched in 1996, now inactive), Mars Odyssey 2001 and Mars Reconnaissance Orbiter. These are American NASA space probes. Europe's active Mars Express (launched in 2003) is currently in orbit of Mars. Russian probes orbiting Mars are Mars 2 and Mars 3 (launched in 1971), Mars 5 (launched in 1973) and Phobos 1 (launched in 1988). None of these are active. Japan launched Nozomi in 1998, but it ran out of fuel and now floats around the solar system around the Sun. FACT TENRocks from Mars have landed on Earth from meteorite impacts blasting debris through space.