9734_cohen.b.qxd 9/3/02 10:15 AM Page 1 ASTROBIOLOGY AND XENOSCIENCE AIN AND ABEL have walked and drifted in many strange places – C ‘walked’ was not appropriate for many of them. Cain is a millipede four feet long, or alternatively one hundred and twenty-two feet along; Abel is – well, more of a gas cloud with a few solid bits, really. Our translator can give some flavour of their reactions to various Earth ecosystems, as they prepare a booklet for alien tourists. (The translator is necessarily imperfect; all alien concepts are replaced by the nearest human equivalent, however inappropriate.) They start, as they usually do, in a desert; it is a simple ecosystem with about species. Abel sinks into the sand, while Cain turns over a flat rock. Under the rock is a small yellow scorpion, whose sting tries to penetrate Cain’s armour and fails. Cain notes that the scorpion is nearly at the top of the ecosystem; he picks up a piece of its excreta and chews it thoughtfully. ‘We should warn them about stings ...and about this stuff,’ he says. ‘It is delicious, and could be addictive. This little chap ate two beetles last week. One was a fungus-feeder, one was a little carnivore; nematode worms, mostly.’ Abel lifts partly out of the sand. ‘About three or four grams of algae every square metre,’ he says, ‘photosynthesising like mad. Lots of grazers on the algae, springtails, lots of kinds of mites ...There’s a fungus mat about ten centimetres down, catching all the excreta, shed skins, corpses; every couple of days it makes a set of spore-bodies at the surface, wafts spores around everywhere; only one in a million hatches, the others are eaten. Now, who’s creaming off the top of this little system?’ Cain burrows feverishly in the surface layers, and reports: ‘Down in that dip there’s a frog who hasn’t woken up for three years. It will be wet enough 9734_cohen.b.qxd 9/3/02 10:15 AM Page 2 WHAT DOES A MARTIAN LOOK LIKE for him this year, he’ll eat a couple of beetles and go down again. And there’s a dry stream bed with lots more life under its stones ...a wind-scorpion who’s just moulted: all it’s had to eat is its shed cuticle; it might take a lizard some time in the next month.’ ‘What is there for the tourists?’ ‘Um ...quite a big gecko ...and with some eggs it’s guarding. And on the horizon, a maned wolf – they’ll like that.’ ‘Enough here,’ Abel declares, as he makes a few notes. ‘More than enough to fill a prospectus.’ ‘Across the gulf of space, minds that are to our minds as ours are to those of the beasts that perish . regarded this Earth with envious eyes, and slowly and surely drew their plans against us.’ In the opening paragraph of his story The War of the Worlds, the great H.G. Wells introduced his Victorian readers to the novel concept of an alien lifeform – a creature from another planet. (Anyone who has listened to the Jeff Wayne musical version narrated by Richard Burton will find ‘minds immeasurably superior to ours’ more familiar, which is less clumsy to the modern ear, but the above is what Wells actually wrote.) The wide Victorian readership of Wells’s books and magazine stories found little difficulty in following his imagination out to the denizens of Mars, busily planning the invasion of Earth. The Victorians revelled in the harrowing tale of blood, death, and destruction as the Martians, disembodied brains enclosed in three-legged walking machines, laid waste to their home planet – or, at least, to England, which Wells pretty much identified as the home of humanity. And they were spellbound by the unexpected ending, in which Earth is saved not by Man, but by microbes. The War of the Worlds still has the power to thrill us, even in its mostly dreadful movie incarnations, and it has given us an icon for creatures from other planets that continues, subconsciously, to influence our thoughts about alien life. Wells also gave us other memorable SF ‘tropes’ – generic story concepts – such as The Time Machine and The Invisible Man, concepts that most of his readers would otherwise not have entertained in all their lives. But there is a big difference between his Martians and those other concepts. Time machines and invisibility are simply fantastic – exercises of the imagination without any correspondence in reality, 9734_cohen.b.qxd 9/3/02 10:15 AM Page 3 ASTROBIOLOGY AND XENOSCIENCE whereas Martians might really have existed earlier in that planet’s history. In fact, as far as Wells knew, they might have been observing the Earth while he was writing his story. Envious eyes and all. The War of the Worlds (H. G. Wells 1897) Earth’s observatories notice a brilliant light on Mars. A ‘falling star’ that lands near London turns out to be a cylindrical spaceship. A Martian emerges – ‘a big, greyish, rounded bulk, about the size of a bear . [it] glistened like wet leather . There was a mouth under the eyes, the brim of which quivered and panted, and dropped saliva.’ Others follow. The Martians construct giant tripodal fighting machines, whose terrible heat-rays terrorise the human inhabitants: Earth is being invaded by aliens. Panic-stricken crowds of refugees evacuate London and head for the coast, but few escape. New machines like metallic spiders, with five legs and innumerable arms, appear. Inside them are Martians, who can now be seen to have the most grotesque appearance – living heads, little more than brains, with huge eyes but no nostrils, their mouths surrounded by sixteen tentacles arranged in two bunches of eight. Having no digestive organs, they take blood from living human victims and inject it into their own veins. They reproduce by budding, like the earthly micro-organism Hydra. Earth (or at least Southern England) is overrun by Martian vegetation, the Red Weed. But there is a fatal flaw in the Martians’ invasion plan. There are no bacteria on Mars, and ‘directly those invaders arrived . our microscopic allies began to work their overthrow . they were irrevocably doomed.’ We now know that there are many planets out there in the galaxy, and we have good grounds for supposing that a number of these will have life. Not all scientists agree with these two statements, and we will discuss – and offer some answers to – their objections later; for now, assume that what we’ve said can be justified. If so, then life as we know it here on Earth is but one sample among many. And our biology, therefore, is but a small sample of all those extraterrestrial biologies. It is the only biology about which we know anything by direct observation, but we really do have a lot of information about its evolutionary history and its variety. Some two thousand years of study, 9734_cohen.b.qxd 9/3/02 10:15 AM Page 4 WHAT DOES A MARTIAN LOOK LIKE? more than half of it carried out in the last twenty years, has provided a large and reliable database against which to test our theories. We have a rapidly growing theoretical biology that sits squarely on our knowledge of life’s history and function, its biochemistry and its adaptations, and to some extent its ecology, here on Earth. Presumably much of this theory can also be applied to life processes elsewhere: the process of natural selection, for example, applies to all simple lifeforms, though perhaps not to those that have organised their environment as human beings have. Over the last decade or so, aliens have become scientifically respectable. Groups of scientists from widely scattered areas of expertise have become interested in extraterrestrial life. Evidence of possible life on Mars has hit the headlines. In a group of NASA scientists headed by David MacKay found tiny tube-like structures in the meteorite ALH, found in Antarctica in . The tubes look rather like fossil bacteria, and there is good circumstantial evidence that the meteorite came to Earth from Mars, splashed off its surface by an impact. These ‘nanobacteria’ proved highly controversial; for a start, they were far smaller than Earthly bacteria. The controversy continues, but few scientists currently believe that the tubes have anything to do with Martian lifeforms. Nevertheless, the claim was taken seriously, and still is. A new science of alien life has been emerging, but unfortunately in its most recent incarnation it has adopted the name astrobiology. It is – or, rather, claims to be – the serious science of alien life. The science is sound, often frontier work: planets encircling distant stars, the latest in genetics. As its name suggests, astrobiology is a fusion of modern astronomy and modern biology. So what’s unfortunate about it? Astronomy is about the stars, and other celestial bodies, and the key area here is the recent discovery of solid observational evidence that proves some stars other than our own have planets. Biology is also about a planet: this one. Of course the planetary aspects are in the back- ground: biology is about living creatures that inhabit our planet. Biology is a vast and impressive subject, currently progressing at a remarkable rate; but in the context of alien life it suffers from one big drawback. It is restricted to those organisms that exist, or have existed, 9734_cohen.b.qxd 9/3/02 10:15 AM Page 5 ASTROBIOLOGY AND XENOSCIENCE on Earth. Because we know so much about these organisms, it is all too easy to think that we therefore know a lot about life in general.