New thoughts on the definition of life

Could alien life exist in the form of DNA-shaped dust?

* 18:09 10 August 2007
* NewScientist.com news service
* Stephen Battersby

'Plasma crystals' that behave like life could exist in Saturn's rings, where the 'dust' would actually be fine ice grains, and the nourishing plasma would be supplied by the solar wind

'Plasma crystals' that behave like life could exist in Saturn's rings, where the 'dust' would actually be fine ice grains, and the nourishing plasma would be supplied by the solar wind.

Could alien life exist in the form of dancing specks of dust? According to a new simulation, electrically charged dust can organise itself into DNA-like double helixes that behave in many ways like living organisms, reproducing and passing on information to one another.

"This came as a bit of a surprise to us", says Gregor Morfill of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. He and colleagues have built a computer simulation to model what happens to dust immersed in an ionised gas, or plasma.

The dust grains pick up a negative charge by absorbing electrons from the plasma and then this charged 'nucleus' attracts positive ions, which form a shell around it.

It was already known that this system can produce regular arrays of dust called plasma crystals, and some experiments have even generated spiral structures. Now, Morfill's simulation suggests that the dust should sometimes form double helixes.

Like DNA, the dust spirals can store information. They do so in the scaffolding of their bodies, as they have two stable states – one with a large diameter and the other with a small one – so a spiral could carry a series of wide and narrow sections.

The specific order of these sections can be copied from one dust spiral to another, like a genetic code. The researchers aren't sure how it happens, but they think each narrow section of spiral creates a permanent vortex of moving dust outside it. So if another spiral drifts alongside it, that vortex pinches the same length into its narrow state.

Genetic code

The spirals even feed, in a sense, as they need fresh plasma to survive and grow, suggesting they may compete with one another for food. Since they are also capable of passing on their genetic code, then perhaps they could evolve into more complex structures.

But that is very speculative, says Morfill, explaining that the simulation is far too simple to include such complex processes as evolution. "It has a lot of the hallmarks for how we define life at present, but we have not simulated life," Morfill told New Scientist. "To us, they're just a special form of plasma crystal."

"It's interesting," says astrobiologist Chris McKay of NASA's Ames Research Center in Moffett Field, California, US.

"Some people have argued that life is a self-organising system [that is out of equilibrium], but you could say that of a hurricane," he told New Scientist. "What these guys have done is one step up from pointing at a hurricane and saying it's a living organism. They argue there's a way this can store information, which is a central feature of life. But it's somewhat disappointing that this is only theoretical work."

"Claiming that something is (or is not) alive is almost pointless because there is no mathematically rigorous definition of life," agrees David Grier of New York University in New York City, US.

Life in Saturn's rings?

The team is now setting up an experiment to find out whether real dust spirals exist. It's tricky, because gravity will tend to disrupt the delicate dust structure, but they can get around that to some extent by compressing the dusty plasma, increasing electrical forces within it. To go much further, they will have to find another way to counteract gravity – perhaps by using magnetic fields, or by putting their experiment in free-fall on the International Space Station.

Alive or not, these dust structures could exist in nature. There are many places in space where small grains of material are immersed in a plasma.

"In our solar system, the places most likely to have the right conditions are planetary rings, especially the rings of Saturn and Uranus," says Morfill. There the "dust" would actually be fine ice grains, and the nourishing plasma would be supplied by the solar wind, channelled by planetary magnetic fields.

But Grier says the dusty spirals may be difficult to form in space, since they require grains of uniform shape and size: "I cannot imagine this will happen in space on a large enough scale to be observable."

If there are any ice-grain creatures roaming the rings of Saturn, though, the pace of life would be leisurely, because plasma-crystal processes run more than a hundred thousand times more slowly than the biochemistry of Earth. So even if they are alive, there's no need to worry about them possessing malign alien intelligence. They probably won't have had time to evolve very far.



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