CultureLab - Life's secrets lie in stars and Petri dishes

Marcus Chown, consultant

WE CAN kid ourselves about big questions. What is the origin of mass? What is dark matter? Does time really exist? But in our heart of hearts there is only one question we desperately want to answer: what is life and how did it come about?

Astrophysicist Dimitar Sasselov argues that we are on the brink of being able to answer this question, and his enthusiasm is infectious.

Sasselov cites two key developments. The first will come as no surprise: the discovery of planets outside our solar system. The total stands at over 700, with new ones being discovered every day. Rarely in the history of science can a field have advanced at such a breakneck pace.

Of crucial importance to the life question, which explains Sasselov's title, is a certain type of extrasolar planet, a super-Earth. These are solid planets of rock and ice between 1 and 10 times the mass of the Earth. We never suspected they existed because, in our own solar system, with its rocky terrestrial planets and bloated gas giants, such bodies are conspicuous by their absence.

It is these super-Earths that are key, argues Sasselov. They are even more attractive as life-bearing worlds than our home planet. They have a relatively small surface area to volume ratio, for instance, so they are better at holding on to their internal heat than Earth. That makes them likely to have the plate tectonics necessary to prevent carbon dioxide from volcanoes building up to dangerous, Venusian levels. If born with sufficient ice, super-Earths may even have giant oceans spanning the surface, 10 times deeper than any ocean on Earth. Think of those as habitats.

But most importantly, according to Sasselov, the surfaces of super-Earths will be at temperatures that permit large molecules to survive over long periods of time and attain the concentrations necessary for the chemistry of life.

What chemistry? Ah, this is where the second development crucial to the life question comes in: synthetic life. More specifically, the creation of a chemical system enclosed in a "vesicle" and capable of life's main functions. According to Sasselov, this field will enable us to overcome our most crippling handicap: that we know of only a single instance of life. It will enable us to explore the limits of biology, to extrapolate from the specific to the general. And here Sasselov sees the two developments feeding off each other. Super-Earths will tell us about the chemical environments for alien life, which will help those seeking synthetic life to zero in on other biochemistries.

And the results of all this striving? To know ourselves, of course. Only by knowing what is possible, says Sasselov in this inspirational book, can we ever understand how life got going on Earth and why it has the characteristics it has. Sasselov quotes T. S. Eliot: "We must never cease from exploration. And the end of all our exploration will be to arrive where we began and to know the place for the first time."

http://www.newscientist.com/