Life off Earth - Do Aliens Exist?

The next big discovery in science will be the proof that alien life exists - and it could come any day now...

A few weeks ago, I put the finishing touches to one of the most visionary projects I've ever been asked to present. The Essential Guide to the 21^st Century is the BBC World Service's flagship series for the start of the new Millennium. My brief was to investigate where science will take us in the future and what are the big discoveries coming up.

In the course of a whistlestop tour from the depths of the CERN particle accelerator under the Alps to NASA's Mars mission control overlooking Los Angeles, scientists predicted some pretty mind-blowing ideas. Around 2020, we'll be wearing mini-computers as fashion accessories, with mini-robots surging around our bloodstream to scavenge viruses. High overhead, astronauts on the International Space Station will be attended by their own colourful, football-sized personal satellites. And, in case A Brief History of Time wasn't enough, we'll have to face the fact that the Universe isn't made of just three dimensions, but contains six or more tiny extra dimensions all curled up on themselves.

But all the scientists I interviewed were abuzz about the biggest story of all. They agreed that this is the millennium in which we will discover intelligent alien life and make contact with it.

NASA The infamous "microbes from Mars". Researchers are still arguing whether these bug like shapes (magnified 100,000 times) are indeed fossilised bacteria.

Bizarre lifeforms

Until recently, we've looked at life in a pretty conservative way. Wildlife films on TV help to reinforce the notion that we and our fellow-creatures live within a fairly narrow range of temperatures and environments, and that, deep down, we all bear a strong family resemblance.

But this complacency has all changed. In just the past three or four years, biologists have discovered that life on Earth can exist in the most extreme places, and in the most bizarre forms. Microbes have been found down boreholes two kilometres deep. They live inside rocks scattered across the freezing wastes of Antarctica. White crabs and giant tubeworms inhabit scalding deep-sea vents that never see the rays of the Sun.

These forms of life may look more akin to "green slime" than to our usual idea of life on Earth. But they are still alive. When life gets started, and wherever, it seems determined to hang on for dear life! So if life got started on our planet and it did so pretty quickly then why not on some of our neighbour-worlds in the Solar System?

Where are the Martians?

Mars has long been a favourite with film directors, yielding untold numbers of B-movie aliens. But many scientists are taking things a little more seriously. Knowing that Mars is a smaller, colder version of Earth, they figure it is a good place to start to search. Mars probably