In 1976 two unmanned Viking spacecraft landed on Mars and dug into the Martian soil looking for signs of life – microscopic bugs, not little green men. Read up on those experiments and you're likely to be told the result was negative. "No life on Mars": so runs the official NASA version. But we're afraid we have to report that this just isn't true!

Each Viking lander had four main experiments. Three of these looked at biological or chemical reactions with the soil, and the fourth – a gas chromatograph mass spectrometer (GCMS) – broke the soil down into its basic atoms.

Two of the 'reaction' experiments – one which tested for plant life and one which looked for gas given off by cells – yielded inconclusive results. The reactions taking place, the researchers agreed, were down to chemistry rather than biology. The third, though, did exactly what you'd expect if there was life on Mars...

The Labelled Release experiment fed nutrient into the soil and tested for any gases released by bugs living there. The result was positive. The principal investigator, Gil Levin, a sanitary engineer by background, used his professional knowledge to test further. He instructed the Viking Lander to heat the soil to 46ºC and the reaction was halved; a temperature of 51ºC destroyed the signal altogether. It was just what you'd expect from using heat to sterilise living cells.

So why didn't NASA celebrate?

Well, the GCMS said something different: it found no sign of any carbon atoms in the soil. Life is made of these atoms, so no carbon equals no life. And that remains the NASA orthodoxy.

But that's not the end of the story. Recently researchers outside NASA – at the Scripps Institution of Oceanography in California – made a concoction of microbes in simulated Martian soil. They fed this concoction to a GCMS, and amazingly the instrument failed to detect the carbon in the bacteria, even though they'd been put there by the researchers.

The Scripps team concluded that the Viking GCMS would have missed microbes living on Mars as well. Their report concludes: "Viking would have missed on the order of 30 million bacteria cells per gramme of soil." That's one hell of a lot of bugs!

There's only one consistent verdict, we believe. Mars does have thinly scattered microbes eking out an existence in its strange soil – too few to trigger a GCMS response, but enough to reveal themselves to the highly sensitive Labelled Release experiment.

"The greatest scientific discovery of the millennium," declares biologist Charlie Cockell, "would be the discovery of no life on Mars!"

Cockell achieved momentary stardom in the British General Election of 1990, when he stood as the Forward To Mars Party candidate against prime minister John Major. He polled 91 votes. More seriously, Cockell has investigated life all over the Earth, from Indonesia (in a microlight) to Antarctica.

He points out that the planets are exchanging meteorites all the time, as asteroid impacts smash rocks out of their surfaces. Scientists have now found dozens of Martian meteorites on Earth, so a fair number of Earth-rocks must have fallen on Mars' red deserts over the aeons. Like miniature space capsules, these rocks must have carried microbes from Earth to Mars.

In Mars' early days it was warmer and wetter than now – ideal conditions for bugs to thrive. Although the Red Planet has now chilled down and is much more hostile, all our experience on Earth is that microbes can evolve to cope with the most extreme conditions.

These 'extremophiles' on Earth can live in the permanently frozen wastes of Antarctica, in ponds as acid as a car battery, in boiling springs, in alkaline wastes, and in cracks several miles underground. The microbe deinoccus radiodurans can even live inside a nuclear reactor.

There's no doubt that rocks from Earth have landed on Mars; no doubt some must have contained bacteria; and no doubt they could have evolved to thrive in even the most hellish conditions. So – as Charlie says – the real surprise would be not to find the descendant of those original bugs living on Mars today....

It was the science story of 1996: newspaper headlines screamed "Life on Mars – Official!" NASA scientists had looked inside a meteorite from Mars and found strange minerals and crystals, and tiny tube-like things that looked like fossilised bacteria. On the other hand many other scientists were quick to criticise their claims.

So what's happened to this story, almost a decade on?

Well, the scientists who believed they'd found micro-fossils from Mars still believe that's what they are – and have more evidence to back their claims. Personally, we think they've got a pretty convincing case. In particular, they've found tiny crystals of a substance called magnetite which are identical to magnetite crystals made inside living cells on Earth – they use them for navigating in the Earth's magnetic field.

But the critics certainly haven't given up. (For more on all the argy-bargy, take a look at our book.) We may not really know the answer until a geologist goes to Mars and takes a first-hand look.

Everyone's heard of the Martian meteorite, codenamed ALH84001, but it's not the only one. Scientists now have over 30 meteorites from Mars.

One fell in France during the Napoleonic wars, sounding like the rattle of gunfire. Another dropped uninvited on a village in Egypt in 1911. There's an urban myth that this meteorite killed a dog – the only case of a living thing being annihilated by a space invader; but Monica Grady from London's Natural History Museum has investigated and found that the poor canine actually died two days before the meteorite fell.

Many others have been picked up several millennia after they fell, in the bleak deserts of north Africa and the Middle East as well as the snowfields of Antarctica.

But be on your guard if someone tries to sell you a bit of Mars. There have been several cases recently of people selling pieces of fake pieces of Moon rock. And you'd need a deep pocket, too. In August 2000 a 4.5 gramme (1½ ounce) piece of Martian meteorite found near Los Angeles was sold at auction for $13,800!

There's another way to look at all those rocks zipping from planet to planet in the early days of the Solar System. Perhaps it wasn't a matter of the Earth seeding Mars with life; perhaps life started on Mars and came to Earth snuggled away inside a meteorite.

Actually, Mars was a better place for life to start. Earth had more powerful gravity, and wayward asteroids smashed into it so violently that the entire planet would have been sterilised – again and again, with each new impact.

Meanwhile the first bugs on Mars would have been living in a tranquil paradise. Small impacts would knock the occasional rock towards Earth, bearing microbes on board.

Once the great bombardment of Earth had stopped, the bugs arriving from Mars could quickly colonise the oceans. They'd evolve into fish, reptiles, dinosaurs, mammals – and eventually humans. In this case, you don't need to search hard to find a Martian: just look in the mirror!

The text books will tell you that the volcanoes on Mars are magnificent, but long-since defunct. That view doesn't square with new images from the Mars Global Surveyor spacecraft. The hot news is that some Martian volcanoes are merely dormant, and will erupt again.

The mother of all Mars' giant mountains, Olympus Mons, is the biggest volcano in the Solar System. It's three times the height of Everest, and is large enough to cover the whole of Spain. It's not much of a challenge for a climber, though, as the slopes are so gradual you'd hardly notice you were walking uphill.

Astronomer-artist Bill Hartmann has pored over new detailed images of the flanks of this huge volcano, and has made a startling find. He expected to find many pockmarks blasted out by meteorites falling down from space, but the solidified lava flows were hardly scarred at all. Since Mars is under constant bombardment from space, Hartmann has concluded that the lava must have flowed very recently.

"It's unlikely this volcanism continued up to the last 1% of the history of Mars and then shut off," he argues. "So the bottom-line inference would be that that volcanism is undoubtedly still going on on Mars. And there will be volcanoes erupting in the future."

Running water on Mars was a big story in mid-2000. It was down to Mike Malin and Ken Edgett, who had installed a camera on the Mars Global Surveyor mission that was able to spy on the Red Planet in unprecedented detail. Malin and Edgett found water-worn gullies that showed no sign of meteorite craters. It meant that water must have been flowing pretty recently – in fact right up to the present day, and into the future.

It was all a bit of a surprise, because Mars is a pretty chilly place. We're talking 50º to 100ºC below freezing point where these gullies run down the hillsides. There's been a lot of discussion about what's going on – you can catch up on the arguments on the web or in our book.

But that's not all. Let's move on from the fleeting appearance of flash floods that carve the gullies. Much more exciting, Mars has liquid water standing on the surface right now in mud-filled lakes. That's not been talked about anywhere as near as much.

Over to Nathalie Cabrol at NASA's Ames Research Center. She's been looking at the lowest-lying points on Mars, where water might have pooled up in the past. Like Malin and Edgett, she began counting meteorite craters to find out how long it's been since these lakes dried out. But there were some that troubled her: lake beds where she couldn't find any craters. "They were young, but at the time I didn't know how young."

She headed down the corridor with to chat with her colleagues Bob Haberle, a Martian weatherman. He was investigating the tropical paradises of Mars: places where the temperature might just rise above freezing on the hottest of summer days. That's a matter of being close to the equator, and also at a low altitude.

Cabrol found that Haberle's tropical hot-spots were in exactly the same places as her young lake-beds. "That's why I believe there is liquid water on Mars today."

It may not even need Haberle's summer sun-traps to keep these muddy lakes liquid. As any motorist knows, all you need is a spot of antifreeze. And there are plenty of lakes in the Antarctic that stay liquid when all around is freezing, because they contain natural antifreeze. "We're looking at 'superbrine';" Cabrol explains; "that's salts of potassium, magnesium and so on. With these you can depress the freezing point to maybe minus 60ºC."

So bring your sunscreen to the beaches of Mars – the planet lacks a protective ozone layer – but bring your duffle-coat too!

OK, we've included the famous Face on Mars... but only to show the latest image from the Mars Global Surveyor which shows exactly what it is. Not a giant sculpture from the ancient alien civilisation, but an eroded plateau or mesa.

But what of the Sandworm? Not many people know about this alien presence on Mars. We were alerted to it by none other than Arthur C. Clarke. Our conversation went like this:

And send the images he did – let us introduce the Sandworm of Mars, clearly visible inside its long glass tunnel.

Or is it? We contacted one of the scientists behind Mars Global Surveyor, Ken Edgett (see the Good Beaches Guide to Mars above). He explains: "It's a trough. The features on the trough are dunes. We see these things – narrow troughs with dunes and ripples in them – all over the planet. For reasons that escape me, those that see a 'tube' are inverting the feature in their minds."

So take a look again. This time turn your head through 90 degrees so you're looking at your screen from the left. Perhaps Ken Edgett has a point....

Long before anyone saw a face on Mars looking towards us, there was a plan to build a face on Earth.

After the Second World War an American artist called Isamu Noguchi worked on several huge schemes, including the gardens for the UNESCO headquarters in Paris. He was haunted by the idea that nuclear war would destroy humanity, and planned a vast sculpture that would inform extraterrestrials that a civilised life form had once existed on Earth.

The vast set of earthworks – sadly never realised – would have depicted a giant human face centred on a nose that was a pyramid a mile long. Noguchi called it Sculpture To Be Seen From Mars....

It was going to be an awful early morning call, as it often is when you're filming for TV. We were due up at NASA's planetary control centre, the Jet Propulsion Laboratory (JPL) near Pasadena in California. But we weren't expecting calls at 5am from the programme's director. "You'd better get to JPL now; they've lost the space probe."

Mars Observer was an all-singing, all-dancing spacecraft designed to unravel the mysteries of Mars' atmosphere and geology – including the role of water – at a stroke. Now it was no more.

It was one of many Martian casualties. Of some 35 Mars missions to date, two thirds have failed – more than the failure rate to any other goal in space. They've become victims of the Curse of Mars.

Amazingly, in many cases the people responsible knew there was a risk of failure, but the launch went ahead anyway. Mike Malin (see The Good Beaches Guide to Mars above) built the camera on board NASA's Mars Observer, and he recalls: "We knew there was a risk in this mission – and that's a story I don't think the public is well aware of. Before the launch it was determined that the valves and the propulsion system had some finite potential of failing."

Mars Observer was basically an Earth-satellite that was sent to another planet. But an Earth-satellite doesn't have to endure months of freezing cold before its engines are fired. By the time Mars Observer arrived at the Red Planet some of the valves were leaking. Fuel and oxidant mixed and exploded, causing the spacecraft to spin out of control.

Even more scary was the story of the Soviet Union's early Mars probes, as we learned from the man responsible, Roald Sagdeev. When he was appointed to head up the Soviet unmanned space programme in 1973 Sagdeev discovered that four massive Mars probes were to be launched within the next three months. And there was a shock in store: "I discovered that the latest tests of the spacecraft systems indicated that some microcomponents or transistors were doomed to fail."

But political inertia overcame Sagdeev's attempts to delay the flights. "The government and we knew we were gambling; it was like Russian Roulette – Russian Martian Roulette." In the event just one of the four probes reached Mars orbit and sent back a few pictures before it too succumbed.

It's not just hardware; computer software is also an ally of the Martian Curse. In 1988 Sagdeev sent two huge probes to explore Mars' larger moon, Phobos. One 'died' en route because an operator sent an incorrect command; more sophisticated software would have picked up the error. And the second disappeared from view on arrival, probably because of an on-board software error.

NASA has had its problems with software too – as we found out quite unintentionally. In 2000 we were travelling from Denver, Colorado, to Washington, DC, and happened to be sitting next to an engineer from the aerospace company that built two NASA probes that had failed spectacularly the previous year. The public report revealed that one had crashed onto Mars' polar ices, while the other had burned up in the atmosphere because – famously – NASA had confused feet and inches with metres. But our travelling companion revealed that the underlying problem behind the public announcements was software: it had been delivered very late in a tight schedule, and had not been adequately tested.

Two more spectacular failures followed: the Russian Mars-96, and Britain's Beagle 2. But they deserve stories of their own....

Mars-96 was a behemoth of a spacecraft. Built by the Russians, it also carried a vast array of scientific instruments from the European Space Agency. Weighing seven tonnes, Mars-96 was actually five space probes in one: a huge orbiter, two landers and two penetrators that would pierce deep into the planet's surface.

In November 1996 a mighty three-stage Proton rocket lofted Mars-96 on the first stage of its journey, into Earth orbit. A fourth stage would then send the probe on its way to Mars.

But the Curse of Mars struck again. The fourth stage failed; the spacecraft was now in an unstable orbit. With the world watching with bated breath, it eventually plunged down safely into the depths of the Pacific Ocean.

Or so it seemed. But the Russians then admitted that Mars-96 had already separated from the fourth stage. What fell in the ocean was the rocket; where was the Mars probe itself?

American analyst Jim Oberg was on its trail. He had worked at NASA's mission control, and he thought that Mars-96 must have overshot the Pacific. Then he came across reports from South America. "There were eyewitness accounts of a fireball that had been seen crossing the Chilean coast at the exact moment that the probe was burning up. They were watching the probe, as it headed towards the Andes Mountains."

Somewhere on the borders of Chile and Bolivia lies the wreckage of Mars-96. Neither the Russians nor the Europeans will admit to it; NASA won't be involved as it wasn't their spacecraft. Not that it would matter, apart from one crucial fact: Mars-96 was nuclear-powered.

Plutonium was to provide the power for Mars-96 on its arrival; and plutonium is not only dangerously radioactive but is also a lethal poison. The small nuclear power-plants were well encased, and would have survived the crash to Earth. But whose hands are they in now?

"The casing could impact a rock and not break open," says Oberg, "Well, yeah – but perhaps it will break open on impact with a chisel. And the tradition in South America is to collect scrap and reprocess it. That material is on the ground, within long hiking distance of the Maoist guerrilla camps in Peru. How's that for a happy thought? What could they do with a couple of hundred grammes of plutonium?"

Beagle 2 was Britain's audacious attempt to sniff out whether there is life on Mars, once and for all, with a single mission. It was carried to Mars piggybacked onto the European orbiter Mars Express. We'll never forget the morning of Christmas Day, 2003. Instead of Santa coming down the chimney, everyone's attention was focused on something equally unseeable: Beagle 2's descent onto the Martian surface.

Beagle could send back no signal until the clamshell-shaped spacecraft opened up. It was all or nothing. If anything had gone wrong with Beagle on the way down - first protected by a heatshield, then lowered on parachutes, and finally bouncing on airbags - we would receive no signal, and the spacecraft's fate would remain a mystery. On the other hand, a signal would mean the spacecraft had survived all the hazards and was working properly - that "the Beagle had landed".

As we all waited in the Press Room in London at 4.00 am on Christmas morning, chief scientist Colin Pillinger was listening intently to a phone, linked up to the giant antennas on Earth that were focused on Mars. Five minutes went by; then ten; after 20 minutes, Colin - with a long face - gently put down the phone and said: "We've received no signal from Beagle 2."

Despite months of trying, not a bark or a whimper was ever heard from the Beagle on Mars. There's been a lot of speculation as to what went wrong. According to the official report, the main problem was probably the Martian weather - Beagle 2 entered the atmosphere in a region where the "air" was unexpectedly thin. One of the instruments on the mothercraft, Mars Express, reported a region of low atmospheric pressure in the region 20,000 to 40,000 metres above the Beagle 2 landing site. In addition, NASA's two rovers, landing a few weeks later, also encountered less atmospheric resistance than expected.

If that's true, the spacecraft probably hit the ground too fast. The airbags burst; and Beagle itself was damaged as it impacted the Martian surface. Until a future salvage mission arrives, all we can hope to spot is a new feature on the Red Planet's surface: according to the team's calculations, if Beagle smashed full-pelt into Mars, it would have blasted out a new crater around 2 metres across, with a halo of debris spreading to a total size of 6 metres….

NASA has plans to send an unmanned probe to Mars to pick up rocks and bring them back to Earth. That's set some alarm bells ringing. If there are living microbes on the Red Planet, will they infect us – creating a virulent Martian plague that threatens humanity?

Step forward John Rummel. He is the man who will protect the world. Rummel is NASA's Planetary Protection Officer.

Part of his job is to stop us infecting other planets, by sterilising NASA's spacecraft before they get sent off. Conversely, his brief also includes preventing other planets from contaminating the Earth. "The plan with the Sample Return Mission," he relates, "is to bring it back to Utah, of all places, and put it in a containment facility. Here it would be assayed to indicate whether or not there's any indication of a biohazard."

The containment facility would be as secure as the labs where scientists study lethal and contagious viruses such as Ebola. Not a single grain of soil would be allowed out until the Martian samples were fully tested.

But Rummel himself is fairly laid-back about the idea of a Martian Plague. On Earth, the most serious bugs evolve along with their hosts. Viruses and bacteria very rarely jump from one species to another. Anything that's evolved on Mars is pretty unlikely to be able to interfere with the way human cells work.

If we do suffer a Martian Plague, Rummel thinks it will be something that returns to haunt us –- Earthly bugs transported to Mars on previous spacecraft and mutated in Mars' harsh climate. "If Earth-life was taken there years earlier, and then we bring it back, I'd want to check it to make sure it's OK."

In Gulliver's Travels, Jonathan Swift writes of the flying island of Laputa, where astronomers have perfected the telescope and know of two small moons circling close in to Mars. The Red Planet does indeed have two moons, in orbits very similar to Swift's description. But they weren't discovered until 150 years later.

Was Swift psychic; or had he been informed by aliens? Well, it's probably not necessary to go those extremes. Astronomers then knew that Mercury and Venus have no moons; Earth has one and – beyond Mars – Jupiter had four moons (another 36 have now been found). So the maths seems to suggest Mars should have two – and they'd have to be small and close to Mars for astronomers to have missed them.

Asaph Hall at the US Naval Observatory discovered the little moons in 1877. Their names were suggested by Henry Madan, the science master at Eton College, England. He proposed Phobos (Fear) and Deimos (Panic), after Mars' attendants in Homer's Iliad. Incidentally, it was Madan's niece who suggested Pluto as the name for the ninth planet when it was discovered by Clyde Tombaugh in 1930.

But these moons harbour one major mystery: no-one knows where they came from. They could be passing asteroids – chunks of space debris – but astronomers can't work out why they ended up in orbit rather than swinging past Mars and back into space. Alternatively, they might be parts of Mars, smashed out of its surface by a cosmic impact.

Either way, they aren't permanent moons. Deimos is gradually spiralling outwards and will one day escape from Mars. Phobos is going the other way. It's moving downwards, and will eventually smash down onto the Martian surface.

NASA has looked into a human mission to Phobos. They say "for the crew, the experience might be likened to working on a large dusty and unequipped spacecraft." In fact, this moon is so cracked that the astronauts may be able to live inside Phobos. On the surface, gravity is so low you'd have to be careful not to jump too energetically, or you'd launch yourself off into space!

There are a lot of problems you need to solve before sending humans to Mars. You've got to get the engineering right, and get the politicians on side. Astronauts will have to exercise seriously to counter the effects of weightlessness. And there's a serious danger from radiation along the way: a solar flare will blast the astronauts with more radiation than an unshielded nuclear reactor.

But all that's the easy part. The real danger in a Mars expedition comes from your fellow astronauts.

The psychological stresses will be unprecedented. One senior NASA astronaut puts it this way: "I always felt comfortable on board the Shuttle. But I've thought about what it would be like to go to Mars, and I don't know if I'm the right person for the job. As you head towards Mars, the Earth gets smaller and smaller, and after a while you're alone in the Solar System."

Yet not quite alone. You are cooped up with a small set of comrades in a very small space for a long time. As psychologist Jack Stuster puts it: "Imagine travelling round England in a motor home with five other people for three years – and you can't go outside."

Stuster considers the flight to Mars as being less like a Space Shuttle flight than one of the long sea voyages of old. "One of the things about isolation and confinement," he says, "is that trivial issues are blown up out of all reasonable proportion." On the Mir space station – though it was comfortably close to Earth – one pair of cosmonauts ended up not speaking to each other except through ground control.

The egotistical and self-motivated 'right stuff' astronauts of the American Mercury capsules would be definitely the wrong stuff for Mars! Stuster admires Ernest Shackleton, the Antarctic explorer, for his skill in selecting compatible crews: "He would interview potential members of his expeditions in a manner that was designed to put them off balance. If they reacted in a defensive way, that might indicate they wouldn't be the best team-mates when things got tough."

Instead, Shackleton would go for the candidate who responded with humour. "It showed they were the kind of person who could get along when the chips were down," Stuster explains. His recipe for choosing a Mars-crew is to put them aboard the International Space Station for several months, to check how they pull together as a team.

Where on Earth would you find a place like Mars? Well, those NASA shots of the Red Planet's deserts might set you thinking of Arizona or New Mexico. But that's entirely wrong. Mars is so utterly cold that you have to look in the Earth's polar regions.

"The Antarctic deserts are ideal analogues of Mars," maintained the late British geologist David Wynn-Williams. "As Mars cooled down, the water receded into ice-covered lakes; then into rocks which contain moisture; and eventually you end up with a desert. That's what we have on Mars at the moment – and that's also what we find in the Antarctic."

The Antarctic Dry Valleys are a far cry from the ice-covered white wilderness we're used to seeing. They are rocky wastelands; permanently frozen, and exposed to the Sun's deadly UV radiation through the ozone hole. Yet here scientists find colonies of living bacteria.

On the other side of the world, north of Canada, Devon Island is another cold and barren waste. Like Mars, it's also been pounded by a giant asteroid impact. And Devon Island is dissected by finger-like lakes and canyons that look strangely Martian.

And here you'll find the first human Mars colonists. They live in a cylindrical 'Mars Habitat', and venture out to work in Mars-spacesuits. A radio link to 'mission control' in Houston has a built-in delay of several minutes, to mimic the delay a real mission would experience in communicating with Earth.

The Habitat is the brain-child of Robert Zubrin, who heads up a public pressure-group called the Mars Society. And it's not just game-playing. NASA has worked with Zubrin and his team to build up experience of working in a Mars-like environment. The project has had its ups and downs – and the set-backs are perhaps more important than the triumphs. "What we've learnt," says Zubrin, "is that when machines break, it's humans who find a way round. On a human mission, the crew is going to be the strongest link in the chain."

Martians – evil little green men, intent on invading the Earth – are part of our culture, nurtured by tales like HG Wells' The War of the Worlds, and Orson Welles' famous radio adaptation of 1938, which caused panic in the streets of New York.

The whole Martian idea was created largely by the Canals of Mars – evidence that the Red Planet had civil engineering works on a scale that dwarfed anything on Earth. The Canals were long straight dark lines crossing the red deserts, apparently to bring water from the polar caps to the equatorial lands.

Spacecraft have now shown that the canals don't exist – there's nothing like them on the surface of Mars. There are just splodges of darker rock scattered around randomly in the otherwise brighter deserts sands. So how did the idea arise?

In 1877, the Italian astronomer Giovanni Schiaparelli described 'canali' – channels – a word taken by Americans to mean manmade canals. Rich Bostonian Percival Lowell built an observatory at Flagstaff, under the clear skies of Arizona. It was equipped with a huge telescope, specifically to map the canals of Mars. And map them he did, in wonderful profusion.

A few years ago, we caught up with another famous astronomer from Flagstaff - the late Clyde Tombaugh, who discovered Pluto there. We asked him how Lowell had managed to see canals which just don't exist. Was it purely an optical illusion?

Tombaugh revealed that Lowell's own observing notes showed that he saw the best canals when he masked off most of the telescope's giant lens. But this also makes the contrast much greater between the darker and brighter parts of Mars, sharpening up the edges in a quite artificial way and leading to the illusion of narrow straight lines.

"Stopping down the telescope like this," Tombaugh surprised us by saying, "I've seen some quite convincing 'canal networks' myself."

There's been a lot of talk about turning Mars into a place fit for humans, by changing its atmosphere and climate – terraforming Mars. But it's a pretty tough job to engineer the alteration of an entire planet. And there are moral arguments against it too, especially if the planet has indigenous life adapted to Mars's present climate.

NASA scientist and Mars visionary Pascal Lee has a different vision: "What may catch up with us faster than the engineering capability for terraforming is progress in genetics."

With the human genome – the "book of life" – now open for any scientist to read, we can expect huge advances in medical science. It also offers the possibility of changing the nature of humans.

"We might be able to adapt human beings and genetically engineer them to live on Mars," Lee continues, "without really changing the planet much." We could evolve long lanky limbs suited to the low gravity, a thick hide to protect us from the ultraviolet radiation, and a digestion system that would allow us to eat oxygen tablets rather than breath Earth-like air.

If – in the far future – life on Earth were extinguished by a cosmic impact, then these strange-looking Martian creatures could be the future of mankind…

In January 2004, NASA's Mars-rover Spirit touched down in the crater Gusev. And something very odd happened soon afterwards.

As the robot craft pulled in the airbags that had cushioned its landing, one of the fabric bags scuffed up the soil in an unexpected way. Instead of scraping along the soil and cracking up the surface - as you'd expect for a dry soil - the airbag rucked up the surface as if it were a rug. It was promptly nicknamed "the Magic Carpet".

Under the rucked-up rug, the soil looked darker. Though NASA's official doctrine is that there's no liquid water near the Martian surface, the carpet's underlay looks for all the world like a layer of mud. And a muddy layer just below the surface would lubricate the motion of the Magic Carpet as it was pulled along.

And what is holding the Magic Carpet together? According to NASA scientist David McKay, the top layer of the soil has a cohesiveness that reminds him of bacterial mats on Earth. Primitive bacteria can stick together in wide thin mats consisting of bacteria and soil particles.

The Magic Carpet could be the remains of a bacterial mat from the early days of Mars's history, when the planet was warmer and wetter. Or it might be living today. McKay says: "I have a lot of trouble figuring out how to tell those ideas apart."

For our money, a dead bacterial mat 2 billion years old would be dry and fragile, like any old fossil. If the mat is flexible today, it must be based on cells that are sticky - and still alive and currently flourishing…