How many craft have been sent to Mars so far?

There have been 38 attempted missions to Mars since 1960, but many didn't even make it off the launch pad. The first craft to make it into Martian airspace made a fly-by in 1965. Getting a craft into orbit is difficult enough, but actually landing a craft successfully on the surface is much trickier, as Beagle 2 found to its cost. Out of nine landing craft that have made it into Martian orbit, only six—including Spirit and Opportunity—have successfully landed.

Why are so many landing right now?

This year was a prime opportunity for a trip to Mars. In August 2003, it was just 56 million kilometres from Earth, the closest it has been in 60,000 years. Mars gets nearly this close every 17 years. But because of the planets' elliptical orbits, Mars and Earth are slightly closer this time round, and will not be this close again until 2287. That’s why NASA sent two ships, while Japan and Europe sent one each.

What are they all looking for?

Water, basically. Mars Express bristles with instruments designed to detect water in the atmosphere, at the polar ice caps, or even under the surface. Previous missions saw areas that looked like dried-up lake beds, such as the Gusev crater. That’s why Spirit landed there—to find out if it really was once a lake.

All this may prove that Mars was once much warmer and wetter—the prerequisite conditions for life. And, for those thinking about eventually colonizing the planet, finding a water mine just under the surface would make long-term habitation much more realistic.

Aren’t they looking for life itself?

NASA isn’t—because they didn’t have the technology when Spirit and Opportunity launched, according to Jan-Peter Muller, of University College, London.

Beagle 2, on the other hand, planned to. It had an instrument on board called a mass spectrometer, which is used to measure the weights of different atoms. Biological processes tend to rely on a lighter form of carbon, so any mineral deposits left by a living creature would contain a higher proportion of this ‘light’ carbon than non-biological minerals. The Beagle team miniaturized a fridge-sized mass spectrometer into something that could fit into the palm of your hand, making it ready for space travel. Sadly, it looks like Beagle 2 won’t get the chance to use it.

Don’t we already know that there is water on Mars?

Sort of. Previous Mars missions have identified geological features that looked as if they were left there by running water. Mars Express has now taken more detailed pictures of canyons showing sedimentary layers, indicating that they were carved out by… something. Some researchers say this is definitive proof that water once flooded the planet.

As for water ice, radar images have suggested there is plenty under the surface. And the Odyssey orbiter saw lots of hydrogen atoms locked into the ice cap at the martian South pole, which scientists thought was bound to be a signal from water ice. Mars Express has now confirmed this by using an infrared spectrometer to detect water molecules themselves.

But we don’t yet know if there is any liquid water on the planet today.

Do we think there might be life on Mars?

A martian meteorite found on Earth was once proposed to contain fossils of alien bacteria. But this has proved highly contentious—some say the squiggles in the rock could have formed without the presence of life.

There is a good chance that Mars was once hospitable, in warmer, wetter days. And life could, theoretically, linger. Bacteria have been found in extreme conditions on Earth. The distribution of moisture in the Arizona desert, which can support life, is quite similar to the surface of Mars. No one really knows where the line is between 'uninhabitable' and 'inhabitable'.

So have these recent Mars missions actually discovered anything new?

Mostly they have confirmed things that we suspected to be true, and have taken pictures and measurements in far more detail than we ever had before.

Mars Express, for example, last week confirmed that Mars is losing molecules of water as it is battered by the solar wind, a stream of high-energy particles thrown out by the Sun. The solar wind strips water molecules out of the atmosphere, leaving a trail of gas behind the planet rather like a comet’s tail. Researchers have long thought this to be true, but now they have seen it in action. The effect could explain where much of Mars's ancient water reserves have disappeared to.

Mars Express has also confirmed that there is water ice at the southern pole.

Can we learn anything about the Earth by studying Mars?

Yes. Mars has a simple atmosphere compared to Earth’s, and it hasn’t been tampered with, letting researchers look more easily at the relationship between things like water vapour and ozone—important in climate-change studies on Earth.

In the 1970s, data from one of the Viking missions was used to work out what happens to a planet’s surface when huge amounts of dust fly up into the atmosphere. Dust clouds block out sunlight, they found, causing a huge drop in surface temperature. This became known as the ‘nuclear winter’ hypothesis, because of the similar effects that a nuclear detonation could cause on Earth.

What is a ‘sol’ and why do researchers keep talking about them?

A martian day. Each sol lasts 39 minutes and 35 seconds longer than an Earth day. The rover goes to sleep at night because it runs on solar power, which means that NASA scientists speak, eat, and sleep according to what time of sol it is.

Is Mars really red?

The Viking landers saw it as a ‘chocolate brown’, while all of the images from Spirit have had their colours enhanced, making it look a bit more red. NASA scientists say that it might take weeks of data gathering to work out the true colour. The red glint as seen through a telescope comes from oxidized iron minerals in the soil—basically, Mars is rusty.

Are these craft ever coming back?

Nope. The solar panels on Spirit and Opportunity will produce less and less power as Mars gets further away from the Sun and dust clogs them up. About 90 days after arriving on the surface of Mars, the rovers won’t be able to store up enough energy to keep warm at night. The rovers will be stuck in place forever—just like other rovers before them.

Orbiting craft last longer. But Mars Express, for example, will eventually be dragged through Mars’s atmosphere to a fiery doom.

The first Mars return mission—where a probe will attempt to come back to Earth with some rock samples—is planned for 2011.

Is anyone worried about all this litter we’re leaving on the red planet?

No one is too concerned about rusting bits of metal on the surface. But people are very careful to make sure that there is nothing more than that contaminating the martian surface—like earthly bacteria.

Since 1967, space-going countries have signed a treaty in which they promise to do everything possible to avoid contamination while exploring other planets. And thank goodness. If they didn’t do this, any life we one day find on Mars might simply be something we took there ourselves.

Will we ever live on Mars?

George Bush seems to think so. He has promised to send astronauts back to the Moon as early as 2015, and no later than 2020, with the intention of building a permanent base. From there we’ll then be able to go to Mars… and beyond, he said. Technologically it is possible. But critics are calling Bush’s statements an election stunt. And everyone agrees it will take immense amounts of money, time and resources to do it.