Washington: Complex chemical activity on the surface of Saturn’s moon Titan has baffled scientists. While some think it’s non-biological chemistry, others believe there might exist some primitive, exotic form of life.
Astro-biologists theorize that the signatures fulfil two important conditions necessary for a hypothesized “methane-based life.” Two findings have revealed hydrogen molecules flowing down through Titan’s atmosphere and disappearing at the surface, and a lack of acetylene.
According to Chris McKay, an astrobiologist at NASA Ames Research Center, Moffett Field, California, acetylene would be the best energy source for a methane-based life on Titan.
One interpretation of the acetylene data is that the hydrocarbon is being consumed as food. But McKay said the flow of hydrogen is even more critical because all of their proposed mechanisms involved the consumption of hydrogen.
“We suggested hydrogen consumption because it’s the obvious gas for life to consume on Titan, similar to the way we consume oxygen on Earth,” McKay said.
“If these signs do turn out to be a sign of life, it would be doubly exciting because it would represent a second form of life independent from water-based life on Earth.”
A methane-based organism on Titan would have to use a liquid medium for living and not water which is frozen solid on the planet. And the list comprises - liquid methane and related molecules like ethane. While liquid water is widely regarded as necessary for life, there has been extensive speculation published in the scientific literature that this is not a strict requirement.
The new hydrogen findings are consistent with conditions that could produce an exotic, methane-based life form, but do not definitively prove its existence, said Darrell Strobel, a Cassini interdisciplinary scientist based at Johns Hopkins University in Baltimore, Md., who authored the paper on hydrogen.
“It’s as if you have a hose and you’re squirting hydrogen onto the ground, but it’s disappearing,” said Strobel, who studies the upper atmospheres of Saturn and Titan.
“I didn’t expect this result, because molecular hydrogen is extremely chemically inert in the atmosphere, very light and buoyant. It should ‘float’ to the top of the atmosphere and escape.”
Strobel said it is not likely that hydrogen is being stored in a cave or underground space on Titan. The Titan surface is also so cold that a chemical process that involved a catalyst would be needed to convert hydrogen molecules and acetylene back to methane, even though overall there would be a net release of energy. The energy barrier could be overcome if there were an unknown mineral acting as the catalyst on Titan’s surface.
“Titan’s atmospheric chemistry is cranking out organic compounds that rain down on the surface so fast that even as streams of liquid methane and ethane at the surface wash the organics off, the ice gets quickly covered again,” said Roger Clark, a Cassini team scientist.
“All that implies Titan is a dynamic place where organic chemistry is happening now.”
“Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed,” said Mark Allen, principal investigator with the NASA Astrobiology Institute Titan team. “We have a lot of work to do to rule out possible non-biological explanations. It is more likely that a chemical process, without biology, can explain these results – for example, reactions involving mineral catalysts.”
First Published: Friday, June 04, 2010, 12:21