Eighty-three per cent of us believe there is, and some believe life originated on Mars. Colin Pillinger outlines efforts to collect data from the Red Planet and considers the implications

The question "where do I come from?" seems to be on the tip of everyone's tongue. It can be answered in a variety of ways. We could be talking about a little harmless genealogy to trace one's ancestors or more problematic issues concerning an individual's right to locate missing natural parents. An answer could also focus on the quest to establish how life began and whether we are alone in the universe.

About 17 per cent of the population believes that life on Earth is unique, the result of some happy accident that we have not yet been able to fathom. This egocentric view has always struck me as being a cop-out; an excuse devised to avoid the alternative. The rest of us (83 per cent) staring at the night sky, contemplating billions of galaxies, with billions of stars (each a nuclear reactor pumping out the essential elements of life, hydrogen, carbon, nitrogen and oxygen), are more inclined to accept that a spontaneous generation must have occurred elsewhere.

There is, of course, another view that has been in vogue for at least a couple of centuries: that life on Earth arose in another place and was brought here by meteorites. If this were true, we might all be Martians - Mars would have been geologically more suited to life developing at an earlier stage in the history of the solar system.

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Within a few years, we may have experimental data to enable us to choose among these speculations.

Both Europe and the United States have set out their stalls with respect to looking for past and present life on Mars. Beagle 2 - the British spacecraft to be launched by the European Space Agency as part of its Mars Express mission - intends to perform its studies in situ . It carries instruments to measure the abundance of water, organic matter and carbonate minerals on Mars.

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The US space agency Nasa's programme, by contrast, is geared up to identifying places on Mars that might yield the right samples, which will be collected for a return to Earth and a detailed investigation. Everybody party to both investigations has agreed to an international protocol that can be paraphrased thus: "You should not take living terrestrial organisms to another body that might be capable of sustaining them."

Sterilising spacecraft is not entirely altruistic - carrying viable organisms on space missions might prevent a future generation of scientists, equipped with better techniques, finding life in all manner of places if we masked it with terrestrial organisms; there could be all manner of false positives. But our main concern is to prevent the havoc extraneous organisms could cause. Remember what rabbits did for Australia.

The other half of the planetary protection decree is: "Nor should you contaminate the Earth." The consequences of one biology meeting another were illustrated by the fate of H. G. Wells's fictional Martians when they encountered terrestrial microbes.

No one is suggesting that any martian sample would be brought to this planet without quarantine arrangements. But quarantine procedures are notoriously incompatible with the cleanliness requirements that are imperative if we are to be certain that the information sought from martian samples is not a result of contamination by terrestrial matter. Without a foolproof solution to this difficulty, the outcome is likely to be a compromise. When Apollo lunar samples were analysed in the 1960s, one scientist volunteered to eat some of the Moon dust if it meant he would obtain the material before anyone else. Volunteers for martian rocks? - there would be plenty.

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There is another scenario: suppose Beagle 2 finds signs of past life on Mars to confirm the tentative observations already made from martian meteorites. Perhaps its mole will reveal an unambiguous sample of organic materials protected from the planet's harsh environment under a giant boulder. Maybe the mass spectrometer will show that the carbon isotopes are fractionated between organic and inorganic phases - mimicking what happened on Earth where such results testify as chemical fossils of living processes that took place nearly 4 billion years ago.

Another prospect is that analysis of the martian atmosphere by Beagle 2 could detect minute quantities of gases such as methane that should not be there unless an actively metabolising community exists on Mars. What would happen next if we found some evidence of life past or present? Naturally, we would want to know if life on Mars had the same biochemistry as us. How did it evolve? Science progresses faster when you have two different systems to study. Beagle 2 has no agreed follow-up investigations in place - we resorted to commercial arguments to obtain sponsors. Would the prospect of extraterrestrial biodiversity stimulate space exploration funding from the multinational biotechnology companies? I rather think it might. Would we want to accelerate or decelerate exploration of Mars by people if there were human health risks?

All this may never come to pass. Mars may be desolate and sterile, except in the eyes of geologists, geochemists, geophysicists and meteorologists. In which case the show will move to the moons of Jupiter - Europa in particular shows evidence of the essential ingredient of Earthly life, liquid water.

And, sooner or later, one of the extrasolar planets will be found to be Earth-like; space telescopes are planned to look for telltale ozone, a signature of life, in far away planetary atmospheres. The search for extraterrestrial intelligence by communication might become mainstream - motivated by inquisitiveness, profit or a desire for military supremacy.

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Looking for the origin of life by travelling away from Earth is not a stroll down to the archives or a visit to the law courts; it will be fraught with difficulties but it cannot and should not be stopped.

Colin Pillinger is professor of planetary science, Open University, and lead scientist in the Beagle 2 project.

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