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The search for alien life

How do you look for something if you don't know what it looks like?

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Widening up the field

Not everyone is sure how helpful all this is. Serena Viti, an astrobiology researcher at University College, London, summarises: "If life is not based on what we know, then it becomes more difficult to know what we are looking for."

The further into the report you go, the wider and weirder the possibilities become: the latest experiments in synthetic biology suggest we might not even have to look for life based on DNA. It even raises the possibility of "non Darwinian life". (On being told this, Professor Burchell chuckles wryly, a man laughing at a private joke. The suggestion that some universally agreed on definition of Darwinian life might already exist is obviously amusing.)

The report notes that experiments in synthetic biology have created structures with six or more nucleotides that can also encode genetic information and, potentially, support Darwinian evolution. It also cites studies in chemistry that show how an organism could tap into other energy sources. A reaction of sodium hydroxide and hydrochloric acid, for instance, would make it possible for a life form to have an entirely non-carbon-based metabolism. 

Put the paparazzi on the case

The authors recommend that the machinery we send out to the furthest corners of our solar system should carry with it an array of detectors capable of sniffing out life of all kinds. Saturn's moon Titan is a high priority for exploration for the authors. The Huygens probe which landed there in 2005 discovered an environment they consider most fertile for weird life in our solar system.

There are problems with this approach, of course, not least the bewildering array of possible life forms we are looking for.

Professor Burchell argues that if we really want to find alien life, we'll have to do it with cameras. This might not be the most obvious conclusion to come to after reading about how life could be far more varied than boring terran life with its dull as dishwater carbon and water based biochemistry, but it isn't a foolish one.

Cameras will be essential in the hunt for ET, because "there is no single definitive test for life", he says.

Finding carbon-based life anywhere is extremely hard. Even on Earth growing a culture in a petri dish requires care, and a probe that has landed on another planet is not exactly a biology lab. Assuming it exists, there are all kinds of ways you can miss it, not least precisely because you don't know what it will be like.

"Take salt, for instance. Some bacteria need it to grow, but it will kill others," Burchell says. His point is clear: send the wrong test and we could get a negative result.

"Sending a test to find life to another planet is very difficult. For a start the test has to be able to do somthing fairly sophisticated: detect respiration, cell walls or genetic material. Then it has to be very small, not mind being shaken about like a James Bond Martini during a rocket launch, the being frozen in space for a journey of many years before being expected to work right out of the box when it reaches its destination."

A team at the University of Leicester, led by Dr Mark Sims, is developing a chip which could test for some indicators of life. But even this would not be exhaustive.

Add to this the new complexity of looking for life that is unfamiliar, and the already formidable challenge becomes truly daunting. Burchell puts his finger on the problem: it is too complicated to test for life remotely, but you can't send an astronaut to do it because you would, in the best tradition of a twisty CSI plot, contaminate the scene.

This is where the cameras come in.

"A better alternative is to send a camera and look for changes. If you see a change, you can try to assign a reason for it. Are the seasons changing and frost melting, or have you observed something else, maybe a biological process," he says.

Viti seems to agree: she argues that alien life might not look very different, even if it is chemically worlds apart: "I think that when we speak about extra-terrestrial life, one has to remember that the most common form is probably non-intelligent, as defined by us, basic form like bacteria and viruses. So, it is hard to imagine how they would look, or whether to our eye they would look like any different from earth bacteria," she says.

A change, though, might be detectable, regardless of the chemistry of the life that produced it. ®

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