The search for ET turns close to home

If life can survive in ocean depths or under ice, then Jupiter, Saturn moons may hold secrets

Times Colonist
Published: Sunday, November 12, 2006

Readers who saw the Jodie Foster movie Contact know all about SETI -- the Search for Extra-Terrestrial Intelligence. Massive radio telescopes aim at the stars, while astronomers listen for a signal that proves we are not alone.

And a laborious search it has been. In the course of more than two decades, tens of thousands of star systems have been checked. Every night computers sort through recordings from 28 million radio channels.

And yet, among all the background noise of decaying stars and colliding galaxies, not a single message has been heard that would point to alien life forms. If the universe is home to other beings, so far, at any rate, they have nothing to say to us.

It could be, of course, that buried in this haystack of recordings is the message we've been looking for. The amount of data produced is so immense, available computer space is swamped.

It would be a cosmic irony if ET is on hold, waiting for someone to pick up the phone. If that thought catches your imagination, and your computer has some free time, you can donate it to the project. Visit the website setiathome.berkeley.edu for details.

In the past few years, a different possibility has begun to emerge. Just conceivably, we've been looking in the wrong places. Evidence is beginning to mount that conditions necessary for life might exist in our own solar system.

Originally, Mars and Venus, our two closest neighbours, seemed the most likely candidates. But Venus turned out to be a hellish 450 degrees Celsius and Mars is an arid, freezing desert. Whatever water may have existed evaporated long ago, or lies frozen deep beneath the surface. Case closed. Or so it seemed.

But recent probes to the outer planets have discovered something entirely unexpected. It appears there is liquid water, and in huge quantities, on at least three bodies. Two of Jupiter's moons, Europa and Callisto, have oceans covering their entire surface. The upper layer of these oceans is frozen to a depth of several kilometres -- about the same thickness as the ice covering Earth's Antarctic Ocean.

Even more surprising, there might be liquid water on, or just below, the surface of one of Saturn's moons. A recent NASA probe photographed what appear to be jets of water venting into space from Enceladus.

How this could be possible, with surface temperatures in each case around minus 300 degrees C, is still uncertain.

But Jupiter and Saturn, the solar system's two largest planets, exert crushing tidal pressures on their satellites. It seems these pressures are sufficient to heat the temperatures of orbiting moons and melt their ice-filled cores. And in the case of tiny Enceladus -- one-seventh the size of our own moon -- the crush is so great that water is forced to the surface in geyser-like spouts.

Until recently, these discoveries might not have raised hopes. Life, at least here on Earth, was thought to require not just water, but light from the sun as well. And little of that reaches Jupiter or Saturn.

But here also, some major rethinking has occurred. Deep sea probes in the Pacific and Atlantic have revealed abundant life forms clustered around volcanic vents in the ocean floor. There is a self-sustaining ecological system, with unique plant and animal species. Yet at those depths, no sunlight at all penetrates; the source of life can only be heat from deep within the planet's core. And it is something very like these conditions that have now been discovered in the depths of space.

Still, there is cause for hope. It appears that living organisms are much more adaptable than used to be thought. Primitive life forms have been found in some of the most hostile paces on Earth, from super-heated thermal springs to frozen ice cores from deep below the Arctic permafrost. The idea that biological life requires warm, sheltered conditions is being replaced with a more rugged picture.

Certainly the moons of Jupiter and Saturn are no Garden of Eden. Some of them are closer to the biblical notion of a nether world, with sulphurous clouds and lakes of methane. Radiation levels on the surface would kill a human being in seconds. It may very well be those environments are simply too hostile for even the hardiest organism to survive.

Nevertheless in these past few years, the odds of finding life elsewhere in our solar system have shortened significantly. And it will be a tangible, knowable form of life.

If we do eventually find an alien message from space, whichever civilization sent it will lie far beyond our reach. There will be no point in replying across the thousands of years a response would take, and no hope of contact.

But if life exists on a neighbouring planet or moon, we already have the means to observe and learn about it. And that is a heartwarming thought.