At 10:02 yesterday ( 15:02 GMT), the space rover Curiosity became the 39th exploratory mission to Mars. Nasa's latest venture left Cape Canaveral, in Florida, with the most ambitious task yet – to find out whether Mars is, or ever has been, suitable for life. There's a lot more that they hope to find out, but how much do you know about the Red Planet? Do you even know why it's red? Here, Matthew Bell guides you through the 39 most interesting facts about the planet, which we might one day call home....
1 Popular belief has held Mars to be the planet most likely to sustain life. In 1900, the French Academy of Sciences offered 10,000 francs to the first person to establish contact with an alien species. But so sure were they of life on Mars that they said contact with Martians wouldn't count.
2 It's the fourth planet from the Sun, after Mercury, Venus and the Earth, but it's only half the size of the Earth, measuring 4,200 miles in diameter.
3 Its mass is also smaller – only 10 per cent of the size of Earth in volume.
4 That means the surface gravity is smaller, only 37 per cent of what we have on this planet.
5 So you would be able to jump three times higher on its surface than on Earth's.
6 Somebody weighing 10st 10lb on Earth would weigh 4st 1lb on Mars.
7 The good news is that water does exist on Mars; the bad news is that it's not in liquid form but vapour or ice. That's because the atmosphere is too thin, being 95 per cent carbon dioxide.
8 There is a large frozen sea on Mars, according to research conducted by the Open University in 2005. Looking at images, they concluded that a region near the planet's equator could be a body of ice just beneath the surface. Previously it had been thought ice existed only at the Martian poles.
9 Even if there's water, no human could survive on Mars because of the low atmospheric pressure. Standing on Mars without a spacesuit, your blood would start to bubble, causing instant death.
10 There's also the problem of Mars having no ozone layer, which means it is exposed to the full force of ultraviolet radiation from the Sun.
11 There have been 38 expeditions to Mars, though no human has landed there. The first, in October 1960, was by the Soviets: Mars 1M, consisted of two unmanned fly-by probes, but they failed to develop enough thrust on leaving Earth, and only got 75 miles before coming back. Only a third of missions to Mars have been successful, prompting speculation about a curse, or a Bermuda-style triangle between Earth and Mars.
12 The first successful fly-by was by the US in 1965, when Mariner 4 took 228 days to get there.
13 Mars's distance from Earth changes by the second because the two planets are on different elliptical orbits. The distance between them ranges from 36 million miles to more than 250 million miles.
14 You can see exactly how far Mars is from Earth in real time thanks to the physics department of Emory University in Atlanta, which has it displayed second-by-second on its website.
15 Scientists talk of average distances between planets, which for Earth to Mars is given as 140 million miles.
16 To give an idea, if you drove there at 70mph, it would take you 228 years and 120 days.
17 In classical history, Mars was the Roman god of war, known as Ares to the Greeks. Festivals for him were held in March, which is how the month gets its name (Martius in Latin).
18 Mars is an important figure in Rome: he was the father of the city's founders, Romulus and Remus. He also had an affair with the goddess Venus, who was the spiritual mother of the Trojan warrior Aeneas, another of the city's founders.
19 Mars is visible with the naked eye and has been documented for 4,000 years.
20 Nicolaus Copernicus was the first to identify Mars and posit the theory that it was a planet – and the first to suggest that the planets orbit the Sun – the so-called the heliocentric theory.
21 The first person to look at Mars through a telescope was Galileo Galilei in 1609.
22 The reason Mars looks red, and is called the Red Planet, is because of the red oxide in the soil. This is a fine talc-like powder, formed on Mars's metallic rocks, which are effectively rusting.
23 The Dutch astronomer Christiaan Huygens was the first, in 1659, to make note of the dark patch on Mars now known as Syrtis Major. He observed it using a telescope he made himself, and drew it in a sketch of the planet.
24 Also known as the Kaiser Sea, Syrtis Major is not in fact water: it's a large shallow volcanic depression covered in basalt rock, which makes it look black.
25 Another big blob visible on Mars is Hellas Planitia, a massive circular impact basin in its southern hemisphere. This was caused by an asteroid hitting the planet during the Late Heavy Bombardment period, about 4 billion years ago.
26 Hellas is the largest known impact crater of any planet in the solar system.
27 Mars sets a few other records too: it has the highest peak in the solar system, Olympus Mons, which at 15 miles high is three times the size of Everest.
28 It also has the largest network of canyons on any planet, known as Noctis Labyrinthus. One of Mars's canyons, the Valles Marineris, or Mariner Valley is 2,500 miles long and 4 miles deep.
29 Mars's crust is much thicker than Earth's and is just one piece, not a series of overlapping plates. So at least there aren't so many earthquakes.
30 Mars does boast the most violent storms, though, with winds up to 125 mph, which can go on for weeks, usually when it is nearest to the Sun.
31 It takes 687 days, nearly two Earth years, to orbit the Sun.
32 Mars has two moons, Phobos and Deimos, which are thought to be asteroids that got trapped in its orbit. They were discovered in 1877 by the American Aspah Hall, though people had long suspected their existence. Their names come from Greek mythology, and mean "fear" and "dread", two characters who accompanied Ares into war.
33 The popular belief that life existed on Mars dates back to 1877, when the Italian astronomer Giovanni Schiaparelli discovered a network of lines on the surface. He called them canali, or "channels", but this got mistranslated as "canals", prompting the American astronomer Percival Lowell to guess that they were used to move water from the ice caps at the poles to the desert. He even wrote a book called Mars as the Abode of Life in 1910.
34 A cult belief in Martians developed, best exemplified in fiction by H. G. Wells's story The War of the Worlds of 1897.
35 Widespread belief in Martians continued well into the 20th century. In 1938, Orson Welles's adaptation of The War of the Worlds was broadcast on radio in America and reportedly caused widespread panic, as so many people thought it was true.
36 The new robot going to Mars, the Mars Science Laboratory, is called Curiosity and cost $2.5bn (£1.6bn). It's the size of a Mini Cooper and has six wheels. It is equipped with drills, tools to scoop up dust samples and a wide-angle camera mounted on top, which can take high-definition film footage.
37 The MSL is heading for a crater near the equator called Gale, which is one of the deepest holes on the planet, deeper even than the Mariner Valley. Scientists are hopeful it will be an Aladdin's cave of mineral samples.
38 Powered by a plutonium battery, Curiosity has the capacity to rove the planet for 10 years, if all goes well.
39 Nobody has ever landed on Mars, but the US is planning a manned landing for the mid 2030s. President Barack Obama gave his support last year, saying he expected to see it happen in his lifetime. But, because of the expense of sending astronauts there and back, it's been proposed that whoever goes to Mars should stay there indefinitely.