It’s life but not as we know it

Tim Radford

On 4 July, the US spacecraft Pathfinder, one of three launched last November, will enter the thin atmosphere of Mars. Though the Martian atmosphere is about 1 per cent of the Earth’s, the buffeting will slow the spacecraft down from 7.5 kilometres a second to about 400 metres a second, or 900 miles an hour – which is slow enough for a parachute to open (rockets will help). Pathfinder will literally bounce into touch, bobbing on a cocoon of inflated airbags, before coming to rest on Martian soil. The touchdown will be in a region called the Ares Vallis, chosen because it seems to be a huge wadi or dried-up watercourse. A hatch will open, and out will pop a little wheeled robot rover called Sojourner, which will beetle about the immediate terrain, examining rock chemistry and reporting back to the lander, which will relay data and pictures back to Earth.

In September, Pathfinder will be joined by a second American spacecraft, Global Surveyor, which will stay in orbit round the Red Planet. The third, a Russian satellite called Mars 96, burned up shortly after its launch: a reminder that in space the smallest errors impose huge costs. The loss, though awful for the British, European, American and Russian scientists who spent years designing the experiments on board, will not make much difference in the long term. Between now and 2005, pairs of robot spacecraft will leave the Earth for Mars every 26 months or so. The ostensible and often-stated reasons for the programme are simple: if we learn more about the climate and history of Mars we will understand more about the climate and history of Earth.

That is the official line: But many people inside space science and most people outside believe something more immediately interesting: that Pathfinder and Sojourner and the Global Surveyor are looking for life on Mars. This is because a team of US scientists announced last August that they thought they could see evidence of bacterial action in a meteorite, found in Antarctica, with a chemistry that identified it as having come from Mars: evidence, in other words, of life on Mars at one time, even if not now. When they made the announcement there were sharp intakes of breath in space science departments everywhere. (Altogether, 12 meteorites have been identified as bits of Mars, chipped loose in a bygone catastrophe – a collision with something big, like an asteroid or comet – which had spun around the solar system before bumping into Earth. A number of meteorites, Martian or otherwise, contain organic chemical compounds.) The claim was tentative, and some dismissed it, but since then other teams have claimed to have seen what might very well be confirmatory evidence. Unfortunately, the experiments and instruments aboard the spacecraft had already been designed and tested. It was too late to think of some really simple and dramatic extra: one of those sensors like the ones in Star Trek that enable you to say: ‘It’s life, Jim, but not as we know it.’ So the Mars probes will be looking for liquid water or evidence of liquid water in the past, and for resources that might support eventual human exploration. There isn’t any convincing evidence of life beyond Earth, but, once again, we are looking, and this time we expect to find it.

In 1969, the Apollo 11 astronauts, returning from the Moon, were freed from their capsule by men in masks and immediately clapped in quarantine, in case they introduced some dreadful alien infection to the planet. Even at the time, Nasa knew there was nothing much to fear. The Moon looked as though it had always been sterile. Robot spaceprobes went further afield. Venus, once imagined as a warm, tropical garden, an Eden for one of C.S. Lewis’s science fiction parables, turned out to be a hellish place: a surface hot enough to melt lead, covered by thunderous stormclouds which rain boiling acid. Mars, the planet on which astronomers once thought they could actually see canals, seemed an unlikely home for life: it was covered by huge dust storms and its polar caps were coated in frozen carbon dioxide. Just over twenty years ago, Viking landers touched down on Mars and sent back their instrument readings. Nothing. No remains of a vanished civilisation, no little green men, no little green plants, nothing. Humans contemplated the consequence. They were alone around their own star. The nearest star to theirs was four light-years away. That is, if you could accelerate a spaceship to 300,000 kilometres a second, which you couldn’t, it would still take more than four years to get to Alpha Centauri, and there was no evidence that any of the stars in that group had encircling planets. Mankind was effectively alone.

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Books referred to in the writing of this piece:

Life on Mars? The Case for a Cosmi Heritage by Fred Hoyle and C. Wickramasinghe (Clinical Press, 222 pp., £17.50, 2 June, 1 85457 041 2).
The Case for Mars: The Plan to Settle the Red Planet and Why We Must by Robert Zubrin with Richard Wagner (Simon and Schuster, 320 pp., £16.99, 3 March, 0 684 81930 9).
Evolution of Hydrothermal Ecosystems on Earth (and Mars?): Ciba Symposium 202 (Wiley, 346 pp., £55, 15 November 1996, 0 471 9 6509 X).
The Rivers of Mars: Searching for the Cosmic Origins of Life by Piers Bizony (Aurum, 190 pp., £9.95, 24 April, 1 854 10495 0).
UFO 1947-97: Fifty Years of Flying Saucers, edited by Hilary Evans and Dennis Stacy (Brown, 272 pp., £16.99, 1 May, 1 870 87099 9).
Life’s Grandeur by Stephen Jay Gould (Cape, 272 pp., £16.99, 7 November 1996, 0 224 04132 0).
Sex and the Origins of Death by William Clark (Oxford, 208 pp., £16.99, 30 January, 0 19 510644 X).