Is There Really Life on Mars
Early next Wednesday morning, an unmanned spacecraft will slip into orbit around the Red Planet. Mars Odyssey - named in honour of Arthur C Clarke and the year 2001 - will check how wet Mars is. Starting from next January, when its orbit has been brought down to a good height for surveillance, Odyssey will look for signs of ice under Mars's soil - or even pools of liquid water on the warmer parts of the planet.
It's the curtain-raiser to a series of probes that will investigate Mars for signs of life. At Christmas 2003, Britain's Beagle 2 will land on the planet's red desert and check if the soil or atmosphere have been modified by living cells. In 2011, a joint Nasa-French mission will take a sample of Mars's soil and send it back to Earth so that microbiologists can check it out for bugs.
But could this all be a waste of money? After all, in 1976 Nasa landed a pair of vastly expensive probes on Mars specifically to look for life. After months of analysis, Nasa published its official conclusion: Mars is dead.
As scientist and writer, I've always toed that pessimistic line. When Nasa researchers in 1996 claimed there were "fossil microbes" in a meteorite from Mars, I was among the disbelievers. But now I've experienced something of a conversion. It was sparked by the decision - along with my colleague Heather Couper - to write a book on our present knowledge about the Red Planet. As we travelled to interview dozens of researchers - American, British, Russian - we found a wave of new thinking about Mars. Bruce Jakosky, a seasoned planetary scientist at the University of Colorado, Boulder, sums it up: "The Mars I'm studying today is not the Mars that I was studying five or 10 years ago."
The breakthrough has come largely because of a Nasa probe that's currently orbiting the planet. The Mars Global Surveyor has had so little media interest that scientists have nicknamed it the "stealth mission". The spacecraft carries a powerful camera built by Mike Malin, a former Nasa employee who has now set up his own company in San Diego.
Malin is difficult to track down: his company lists no street address. It's because his camera has revealed that the so-called "Face on Mars" is not a giant artificial sculpture but a naturally eroded plateau, and he's constantly pestered by "face-freaks" convinced of some conspiracy to cover up signs of an alien civilisation. "Mars is neither the Earth with craters nor the Moon with an atmosphere," Malin explains. "Mars is Mars. Mars is its own unique planet that has its own unique way of telling us things about itself."
And some of the things it's telling us are turning our preconceptions on their head. Mars has huge volcanoes, which geologists have always thought are extinct. But the detailed pictures from Mars Global Surveyor show fresh lava flows on the flanks of the biggest volcano, Olympus Mons.
But the biggest surprise from the new pictures was water-worn gullies running down the sides of canyons and craters. They appeared so fresh that they could have been eroded yesterday. "They are incredibly young, geologically speaking," says Malin. "We could be talking about a couple of million years ago, or it could be right now."
Ken Edgett, a colleague of Malin's at Malin Space Science Systems, is also a natural sceptic. "I had to be dragged kicking and screaming to this conclusion," Dr Edgett says. He is convinced that there are so many gullies all over Mars that they couldn't all have flowed until a couple of million years ago, and then all switched off in unison. Like the volcanic eruptions, water must still occasionally well up from within Mars, and tinkle down the desert soil to erode fresh gullies.
But temperatures on Mars are well below freezing point. How can liquid water flow? Nasa researcher Nathalie Cabrol thinks the answer is natural antifreeze. "You can have liquid water there if it's a superbrine," she explains, "that's water loaded with salts of potassium, magnesium and so on. …