Move over Darwin

IT'S only a few feet across, weighs a paltry 30kgs, and when fully powered has just enough juice to keep an electric lightbulb going for an hour. Yet inside its clam-like exterior lies the potential to answer the question that has tormented humanity for centuries: is there life on Mars?

Just before 7pm GMT on Monday, the European Space Agency's Mars Express mission is due to launch from Kazakhstan on a Russian Soyuz/Fregat rocket. On board is Beagle 2, a lander designed and built by a British consortium.

More than six months later, just before 3am on Christmas morning, the Beagle 2 is scheduled to land, or, rather, bounce on a set of inflatable air bags, at a site called Isidis Planitia. Over the following days and weeks, Beagle 2 will carry out a series of experiments which could prove, once and for all, whether there was, or still is, life on Mars.

Beagle 2 was named after HMS Beagle, the ship which took Charles Darwin around the world and led to him writing On the Origin of Species, which revolutionised our idea of life and put forward the theory of evolution. The 21st century version is the brainchild of Professor Colin Pillinger of the Open University, who leads the British consortium of universities, researchers and industry.

"It is a tiny lander but it has got a very sophisticated set of instruments on board, the primary aim being to detect whether there was life in the past on Mars, and whether there still is any now," says Prof Pillinger. "The instruments are there to characterise the rocks, so we know their chemistry and mineralogy, and what they look like under a microscope. We will cut samples from them and look for the relic matter of living organisms."

The actual tests are similar to those carried out to search for oil on the Earth: looking for traces of water deposits, and, if there are any, it is possible to detect whether there were any living organisms in the water. These organisms show up as a residue, in the same way as those which break down into petroleum show up.

Beagle 2 will not be the first spacecraft to land on Mars and search for signs of life. In 1975, the two Viking spacecraft concluded there were no signs of life after analysing rocks and soil on the surface of the planet.

But one of the advantages of Beagle 2, giving it the edge over its Nasa predecessors, is the Mole, a device able to burrow beneath the surface of Mars.

"The surface of Mars is a very hostile environment, and anything on the surface will be destroyed. We have to get down below the surface, or, better still, underneath a big boulder," says Prof Pillinger.

After the Viking missions and their apparent lack of success in finding life, interest in expeditions to the Red Planet dwindled, but was revived almost 20 years ago with the discovery that meteorites on Earth had come from our neighbour, and these meteorites were found to contain water, a pre-requisite for life.

"We have analysed these rocks and can say many things about them, and one is that they contain evidence that looks like evidence of past life," says Prof Pillinger.

"The problem is, we cannot say that past life occurred on Mars, so the reason to go back is so we can repeat these experiments in a place where we can dismiss the possibility of contamination."

The lander itself has an insulated outer casing, built to withstand the impact of landing and temperatures of down to minus 70 degrees C, with the lid and base joined by a hinge, which will open the clam once it has landed. The inner shell of carbon-fibre skins on an aluminium honeycomb combines resistance to radiation exposure with as little mass as possible.

The lander is powered by lithium batteries, charged by five solar panels, which fold out from the lander once it has touched down. Energy losses are kept to a minimum by conducting many of the experiments at night.

But Beagle 2 will not be the only mission to Mars this year. Prompted by a favourable launch window - in August, while the spacecraft are en route, Mars will be closer to the Earth than any time over the last 60,000 years - both Nasa and Japan are heading that way.

Nasa's two Mars Explorer rovers are now on the launch pad at Cape Canaveral in Florida, and the Japanese probe Nozomi is already on its way, all due to reach the planet in December.

Nozomi, which was launched four years ago but was forced to take a circuitous route after using too much fuel, will remain in orbit, studying the Martian atmosphere.

But the two Nasa landers will, along with Beagle 2, be aiming for sites which look as though they were fashioned from flowing water, as well as being near the equator to maximise the light their solar panels receive.

Nasa's Rover A, due to be launched next Friday, is aimed at the Gusev crater - an ancient impact crater up to 1,600 metres deep and 150 kilometres across, at the end of a 900 kilometre channel. Rover B, to be launched on June 25, will go to a region called Meridiani Planum, also in the Martian tropics.

In 2000, infrared cameras on Nasa's Mars Global Surveyor spacecraft made an unexpected discovery at the site - crystalline haematite, a form of iron oxide. On Earth, haematite crystals usually form in iron-rich water in lakes and seas. If that was the case here, then Meridiani must once have been flooded. However, it is also possible that the crystals could have been formed when hot lava comes to the surface, without any contact with water.

Whatever its scientific significance, Rover B's cameras are likely to beam back pictures of a truly alien landscape. The surface of the landing site is expected to be grey, not rusty red like most of Mars, with shiny smooth outcrops of haematite that almost look metallic.

But the hopes of British scientists are riding on the Beagle 2, and one feature of its landing site is a large number of small volcanic cones, some just 20 metres across. On Earth, similar cones are formed by magma coming into contact with underground water and exploding. Geologists believe the surface of this site is only ten million years old, and there might still be water ice near the cones.

But again, there could be another explanation; the cones could have been made by carbon dioxide ice meeting lava in the Martian soil. Although carbon dioxide usually turns directly from a solid to a gas, the conditions on Mars might allow it to flow as a liquid.

But it is questions like this that Beagle 2 could answer, the realisation of a seven-year dream for Prof Pillinger and his team.

"I never doubted this would happen. Other people might have done, but my feeling was that it was so worthwhile that we would get there," he says. "We're not anticipating anything - all we can do is design the best experiments and see what happens. We're doing our best, but we never get a chance to get excited."

While Prof Pillinger may not have time to be excited, the culmination of his work could provide the most startling news on life since Darwin.

* For more information visit www.beagle2.com

The facts on Mars

Its reddish colour is the result of iron oxides spread across its surface and gave rise to its name, after the Roman god of war, with its colour reminding people of blood.

It has two moons - Phobos, meaning fear, and Deimos, meaning panic, after the horses which drew Mars' chariot.

A Martian day lasts 24 hours and 37 minutes and it orbits the Sun once every 687 Earth days.

Mars, the fourth planet from the Sun, is 4,212 miles in diameter, just over half the diameter of Earth, and its gravity is about one third that of Earth.

The sky on Mars appears pink, the re sult of fine particles of red dust suspended above the surface.

Its polar icecaps were discovered by Italian astronomer Cassini in 1666.

The atmosphere on Mars is predominantly carbon dioxide, with nitrogen, argon and traces of oxygen.

Surface temperatures range from minus 84 degrees C at night to minus 29 degrees in the afternoon.

On August 27 this year the distance between Earth and Mars will be less than 34.65 million miles - the closest they have been for almost 60,000 years.

There have been six US missions to Mars: the four Mariner spacecraft from 1964 to 1971, and the two Viking craft, which launched in 1975.

Viking Lander 1 became the first spacecraft to successfully touch down on another planet on July 20, 1976.