Hints of unexpected chemical activity on Saturn's moon Titan have sparked speculation that there may be alien life there. The new measurements, reported earlier this week, are intriguing. Taken alone, however, they don't constitute evidence of extraterrestrials. New Scientist examines what it will take to settle the question of life on Titan.
What's all the fuss about?
Titan's surface is a frigid -178 °C, too cold to sustain liquid water. But life may have been able to find a toehold nevertheless. In 2005, researchers suggested that organisms might survive in this inhospitable environment by breathing hydrogen and eating organic molecules such as acetylene and ethane. Now the Cassini spacecraft has found evidence that there's less acetylene on Titan than we would expect, and that levels of hydrogen may be actively being depleted at the surface – raising the possibility that exotic life forms are consuming these substances.
Sounds like evidence of life to me…
It is consistent with the existence of a proposed life form that might conceivably eke out an existence on icy Titan. That's a far cry from evidence that there is life on the moon.
So what else could be causing the unexpected chemical activity?
The mostly likely explanation is that the model used to estimate the flow of hydrogen in Titan's atmosphere from the Cassini measurements did not accurately simulate conditions on the moon, says Chris McKay of NASA's Ames Research Center in Moffett Field, California, one of the researchers who first proposed the acetylene-munching organisms.
This may mean the model overestimated the amount of hydrogen reaching the surface of Titan, which would make it seem that something is consuming hydrogen when it isn't. Another alternative is that Cassini's measurements are more uncertain than we think.
OK, but what if further models suggest hydrogen really is disappearing?
This still wouldn't be evidence of life. There is also the possibility, says McKay, that hydrogen is being consumed through a non-biological process, such as a reaction with acetylene to make methane. It seems unlikely, because catalysts such as copper and iron, which are needed for this reaction, are not thought to be present on icy bodies like Titan, nor very effective in extreme cold. But it's certainly a possibility.
So what are the next steps?
So far, only one model has been used to estimate hydrogen flow on Titan. Once others are used and more Cassini data comes in, we'll have a better idea about whether hydrogen really is being depleted at the surface.
If it is, experiments that simulate Titan conditions on Earth could show whether catalysts that help hydrogen and acetylene react with one another might work on Titan.
Would that be evidence for life?
No. Several missions to Titan's surface would be needed to find unambiguous evidence for life. One of the first steps may be to send a robotic lander equipped with a mass spectrometer, which could look for complex organic molecules – Titan analogues of molecules like ATP and chlorophyll – that could provide additional evidence of life.
A team of researchers is asking NASA to fund one such spacecraft, the Titan Mare Explorer. If accepted, it will launch in 2017. A larger Titan mission that would include a balloon and lander was deferred by NASA last year in favour of first sending two probes to explore Jupiter and its moons. These will lift off in 2020.
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Oil Be Back!
Fri Jun 11 18:07:18 BST 2010 by T R
Is it me, or does this put the Gulf of Mexico into new perspective? What looks like an oil spill to us may just be the advance force for a hydrocarbon invasion force!
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