Life on Titan may be smelly and explosive

09:14, April 13, 2010      

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Scientists have yet to find life beyond the confines of Earth but Saturn's largest moon Titan is becoming the focus of increased interest.

However if life were to be found, it would not be life as we know it. A commonly held belief is that life could only evolve on worlds where water is prevalent. But some scientists suggest Titan may be an exception to that rule.

Although nothing has yet been found to suggest life on Titan, research by astrobiologist William Bains suggests that if life has evolved on the frozen surface of Saturn's moon it would be strange, smelly and explosive compared to life on Earth. Dr Bains will present his work at the National Astronomy Meeting in Glasgow on Tuesday April 13th.

"Life needs a liquid; even the driest desert plant on Earth needs water for its metabolism to work," Bains says, "So, if life were to exist on Titan, it must have blood based on liquid methane, not water. That means its whole chemistry is radically different. The molecules must be made of a wider variety of elements than we use, but put together in smaller molecules. It would also be much more chemically reactive."

Titan is, in many ways, the closest object in the solar system to Earth itself. It has an atmosphere which is so thick that it obscures the moon’s surface in a perpetual orange haze. It has rain, rivers, and lakes, making it the only other world in the solar system known to have liquid on its surface. And it’s clouds and seas are thick with hydrocarbons, the building blocks that, when combined, formed life on Earth.

However, the temperature on the surface is -180 degrees Celsius. Water is permanently frozen into ice and the only liquid available is liquid methane and ethane, which the Cassini/Huygens mission has shown is present in ponds and lakes on the surface of the moon.

"Terrestrial life uses about 700 molecules, but to find the right 700 there is reason to suppose that you need to be able to make 10 million or more. The issue is not how many molecules you can make, but whether you can make the collection you need to assemble a metabolism, Dr Bains says, "It is like trying to find bits of wood in a lumber-yard to make a table. In theory you only need 5. But you may have a lumber-yard full of offcuts and still not find exactly the right five that fit together. So you need the potential to make many more molecules than you actually need. Thus the 6-atom chemicals on Titan would have to include much more diverse bond types and probably more diverse elements, including sulphur and phosphorus in much more diverse and (to us) unstable forms, and other elements such as silicon."

Even if life were to be found on the distant world, it would be quite basic. "Rapid movement or growth needs a lot of energy, so slow-growing, lichen-like organisms are possible in theory, but velociraptors are pretty much ruled out," said Bains.

Dr Bains, whose research is carried out through Rufus Scientific in Cambridge, UK, and MIT in the USA, is seeking to work out just how extreme the chemistry of life can be. Any creatures found on Titan would be strange indeed. "Hollywood would have problems with these aliens," says Dr Bains.

"Beam one onto the Starship Enterprise and it would boil and then burst into flames, and the fumes would kill everyone in range. Even a tiny whiff of its breath would smell unbelievably horrible. But I think it is all the more interesting for that reason. Wouldn't it be sad if the most alien things we found in the galaxy were just like us, but blue and with tails?"

Several scientists are working on a potential Titan lander that would splash down in one of the moon's seas and take readings on its chemistry for 16 Earth days. The so-called Titan Mare Explorer has yet to be approved or rejected by NASA.

Source:Xinhua/Agencies

(Editor:梁军)

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