At 5.35am local time next Friday, a Nasa spacecraft named Phoenix is set to blast off from Cape Canaveral in Florida and begin a 423m-mile journey across the solar system.

After travelling through space for 10 months, it is hoped that Phoenix will finally be able to answer one of science’s biggest questions by discovering once and for all whether life ever existed on Mars.

Launched on the back of a Delta II rocket, the $420m craft must first burst through the Earth’s atmosphere before using the sun’s gravity to slingshot towards the red planet. It will land in an as yet unexplored area called Vastitas Borealis, the arctic plain at the far north of Mars. Using robot testing equipment it will begin, in May 2008, examining the planet’s soil and atmosphere looking for signs of past or present life forms, as well as water. Or so Nasa hopes.

Discovering more about Mars has become the holy grail of space exploration, yet since the 1960s only six of the 37 missions to the planet have successfully transmitted data back to Earth from the planet’s surface. This high failure rate has even led some at Nasa (if only jokingly) to speculate that there exists a so-called Great Galactic Ghoul that swallows up Mars probes. Others talk of a Mars curse that is preventing us from properly exploring the planet.

The reality is that sending a spacecraft to Mars is complex enough in its own right – a favourable window for such launches only appears for a short period every 26 months when Earth and Mars are brought closest together by their orbits, and space travel is fraught with technical difficulties.

This is before you even factor in the challenge of landing a probe on a planet with an extremely thin atmosphere, where the surface is constantly ravaged by solar winds and dust storms and the temperature stays well below zero. Just ask Professor Colin Pillinger, the boffin behind the British Beagle 2 mission, which in 2003 failed spectacularly to put a working probe on Mars.

“The entry, descent and landing is by far the riskiest phase of the mission,” says Peter Smith of the University of Arizona’s Lunar and Planetary Laboratory, who is the principal investigator of the Phoenix mission. “Although it only lasts seven minutes, hundreds of actions must take place in a carefully organised series of events to lead to a safe landing.”

These include deploying a parachute to slow down the descent from an initial speed of 12,750mph to just 5mph, jettisoning the heat shield after resisting temperatures of several thousand degrees, activating the radar, taking readings of the atmosphere and the careful use of 12 thrusters for added deceleration.

If all that succeeds and the Phoenix lander’s three legs touch down on the surface, the real work can begin. The Phoenix, with a deck diameter of just under 5ft, is fitted with two decagonal solar arrays, which will be deployed and convert solar radiation to electricity and power the probe’s onboard instruments.

A pair of rechargeable lithium-ion batteries will provide power storage, while the lander will be in regular radio contact with Earth, using an ultra-high frequency transmitter. The signal will be relayed via two Mars orbiters – the Mars Odyssey and Mars Reconnaissance – which are currently circling the planet. The Phoenix is expected to have an operational life of 90 Martian days (the equivalent of 92 Earth days).

Finding evidence of life will not be easy. The signatures for organic molecules are subtle and can be confused by space debris, or material inadvertently imported from Earth. To guard against this, crucial parts of the probe are covered in a biological barrier wrap and have been heat sterilised. “We have gone to extraordinary lengths to maintain clean surfaces,” says Smith, “but the Earth is filthy with microbes and organic material.”

Despite these problems there are tantalising reasons to return to Mars. In 2002 the Mars Odyssey mission surprised everyone by identifying water ice beneath the ground at the planet’s poles. Phoenix is the next stage of Nasa’s “follow the water” policy, and the space agency expects to find ice within 4in of the surface. This is why a landing site was specifically chosen on the Martian arctic plain, comparable in latitude to Greenland, where no other probe has landed before. Its arrival also coincides with the Martian spring so there will be no frost and longer sunlight hours for the lander’s solar panels.

The panels will charge the batteries that power Phoenix’s sophisticated testing equipment including its 7ft 8in robotic arm made from aluminium and titanium. If all goes according to plan, the arm will bore 20in into the planet’s soil to grab undisturbed samples from beneath the surface. Any water ice will be heated in miniature ovens to check for hydrogen and carbon-based chemicals – the building blocks of life.

The only other tests for organic compounds were made by the two Viking probes in the 1970s. They found nothing, but their ability to sniff out minute traces of organic chemicals was much less sophisticated.

So will Phoenix provide a definitive answer of whether there is life on Mars? Smith is optimistic: “If Mars cooperates and we can find clear signatures that water has modified the mineral and chemical composition of the soil, then yes.”

Mars mission highlights

Mariner 4 (launched 1964, US) After five failed missions by the USSR, Nasa’s Mariner 4 made the world’s first Mars flyby in 1965

Viking 1 and 2 (1975-87, US) Nasa’s Viking landers were the first probes to land on Martian soil and returned some 50,000 images

Mars Pathfinder (1996-97 US) Pathfinder’s Sojourner rover captured the global imagination with its extraordinary images from the Martian surface, many of which were published on the web

Mars Climate Orbiter (1998, US) Nasa’s most embarrassing failure, the $125m spacecraft burnt up in the Martian atmosphere due to human error

Mars Express (2003-, European Space Agency) Europe’s Mars mission is currently orbiting the planet examining the atmosphere and geology. Its lander, Beagle 2, memorably failed in 2003

Mars facts

1.5 times farther from the sun than Earth

Roughly half the size of Earth

Gravity only 38% of Earth’s

Revolves around sun once every 687 Earth days, so a Martian year is nearly twice as long

Surface winds up to 80mph, plus frequent dust storms

Surface temperature averages -53C but falls as low as -128C

Highest point is the Olympus Mons volcano, 16 miles high

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