Paul McAuley

A very common early twenty-first century condition is that of disappointed or diminished expectations. Here we are in 2001, the future of science fiction's Golden Age, and we don't have the aircars, jetpacks, vastly ambitious space programs, and homicidal computers we were promised. Not to mention, of course, aliens willing to meddle in human evolution, or even their black monolithic stand-ins.

Even so, not since the end of the space age have there been so many science-fictional headlines in the newspapers: planet-busting asteroids; worlds around other stars; cloning (my favorite headline generated by the cloning of Dolly the sheep, a headline guaranteed to falsely raise expectations, was "Soon we will be able to raise the dead"); obsolete space stations crashing into the Pacific Ocean; and, of course, life on Mars.

Not the cold, inhuman intelligences of H.G. Wells' War of the Worlds, or the belligerent warrior-races of Edgar Rice Burroughs, or the mournful aesthetes of Ray Bradbury's The Silver Locusts (killed off by culture shock and McDonald's-ization); not even the modest splotches of a few hardy lichens hugging the sunny side of some deep equatorial canyon. No, the reality is nothing more than the fossilized remains of incredibly tiny bacteria associated with smears of organic material deep inside a meteorite -- famously designated ALH84001 -- that was knocked off Mars by a glancing impact some 15 million years ago. And it is entirely possible that the fossil "bacteria" might be nothing more than inorganic crystalline deposits, and the organic material might be due to contamination after the meteorite hit the Antarctic ice cap.

The best we can expect of life on Mars, it seems, are contentious traces of bacteria which, even if they had existed, (1) died out billions of years ago, and (2) were so small that most other bacteria would have no trouble kicking nanosand in their endcap filaments.

Talk about your basic twenty-first century diminishment of expectations. If science fiction writers are going to spin fictions about life on Mars, they had better learn some microbiology, and they had better find some way of making the small and insignificant interesting. How much easier H.G. Wells, Edgar Rice Burroughs, and Ray Bradbury had it!

But the possibility that bacterial fossils were able to travel from Mars to Earth inside a chunk of rock hints at an intriguing possibility: suppose live bacteria could have traveled the same way?

Bacteria can be incredibly hardy. Forty-million-year-old bacteria have been extracted -- and cloned -- from inside a bee preserved in amber. Bacterial spores were recently isolated from water trapped in a billion-year-old salt crystal -- and the spores produced living bacteria. The Apollo 12 astronauts recovered viable bacteria from Surveyor 3 after it had spent two-and-a-half years on the Lunar surface. Experiments show that bacteria, by their very small size, could survive the 10000g acceleration needed for a rock to be blasted off Mars at escape velocity by an asteroid impact, and that some species are very resistant to raw solar radiation. If protected inside a layer of rock, they can survive in the vacuum of space for up to several thousand years. The cold of space, by the way, isn't much of a problem. Between Earth and Mars, sunlight keeps objects at about minus 50 degrees centigrade -- the temperature inside a laboratory freezer -- and viable bacteria are often stored at even lower temperatures. And although the outer layers of a meteorite are heated by friction when it enters the atmosphere, rock is a good insulator and the inside remains cool.

Suppose that there once was life on Mars. It now seems very likely that life on Earth arose almost as soon as the crust had cooled to acceptable temperatures. Mars, a much smaller body, would have cooled more quickly, and if conditions were right, life would have arisen there before it had a chance to do so on Earth. Four billion years ago, inner solar system bodies, including Mars, were undergoing intense meteoritic bombardment. Perhaps at that time many life-bearing rocks were knocked off Mars and eventually fell to Earth. Only one Martian bacterium would have needed to survive. The descendants of that single bacterium -- the Solar System's first successful astronaut -- could have flourished here on Earth while life on Mars died out, or retreated to a last stronghold.

The millions of species living on Earth could all be descendants of that microscopic Martian pioneer. What would happen if, four billion years later, astronauts brought back Martian life, which shares a common ancestor with life on Earth? This notion was the seed of my novel The Secret of Life, but there are other variations on the same theme. Perhaps there's life on Mars -- but it came from Earth, not Mars. Billions of years before the first human colonists reach Mars, it had already been colonized by hardy, microscopic pioneers. Perhaps other bacterial pioneers have colonized every habitable corner of the Solar System -- the subsurface oceans of Europa and Enceladus could harbor ecologies derived from the same primordial ancestors as ourselves.

It is even possible that bacteria could travel between stars. Bacteria permeate the Earth's biosphere -- all the way up to the top of its atmosphere. Solar winds could on occasion strip some of the wispy upper layers of the atmosphere and send the puffs of gas -- and bacteria and bacterial spores -- into space. The same solar winds would propel the microscopic spores outward, towards interstellar space.

It's not an original idea: it was first proposed by the Swedish chemist, Svante Arrhenius, who called his theory panspermia. He suggested that bacterial spores wafted through the Galaxy by starlight could have given rise to life on Earth, and by implication, to life on other planets of other stars.

Needless to say, it would be a very difficult journey. Bacterial spores would have to survive millions of years in hard vacuum and temperatures approaching absolute zero, and would also have to survive the drenching of ultraviolet light when approaching another star. One possibility is that they could be protected by something as simple as soot. G-type stars like the Sun start to eject carbon grains as they age; like banked furnaces, they grow smoky. The microscopic carbon grains could accrete around bacterial spores, and this coating of soot could help the spore survive ultraviolet light as it approached a new star.

Again, only one microscopic star voyager would need to find a new home and survive in it to begin a new cycle of life. And even if it was dead on arrival, if its RNA fell in a suitable prebiotic soup, it could kickstart life.

Bacteria could have been the first interstellar astronauts.

We could truly be children of stardust.

Paul McAuley's books have that ring of authority that tells you the author is not just making this stuff up, he knows what he's talking about. He has a Ph.D in Botany, has worked as a researcher in biology in various universities, including Oxford and UCLA, and for six years was a lecturer in botany at St Andrews University in Scotland.

His first novel, Four Hundred Billion Stars, won the Philip K. Dick Memorial Award, and Fairyland won the 1995 Arthur C. Clarke Award for best science fiction novel published in Britain and the 1996 John W. Campbell Award for best novel. He has also won the British Fantasy Award, and the Sidewise Award for Alternate History fiction. Most of the time he lives in London.