Brussels, 26 Jul 2005
Scientists are preparing to use data collected as the European Space Agency (ESA) probe Huygens descended through the atmosphere of Titan to see whether there is methane-producing life on the Saturnian moon.
Titan's atmosphere is five per cent methane, and Chris McKay of NASA's Ames Research Centre, together with Heather Smith of the International Space University in France, believes that some of it could be coming from methanogens - methane-producing microbes.
To test the theory, the pair worked out the likely diet of such organisms. They argue that the microbes would breathe hydrogen rather than oxygen, and eat organic molecules that drift down to the surface from the upper atmosphere. Of three possible candidate molecules, they argue that acetylene is the most likely as it yields six times as much energy per mole.
Dr McKay and Dr Smith calculate that if methanogens are thriving on Titan, their breathing would reduce hydrogen levels near the surface to one-thousandth of that of the rest of the atmosphere. Therefore, detecting such a variation in hydrogen levels would provide compelling evidence for life on Titan, as no non-biological process on Titan could affect hydrogen concentrations to such an extent.
The chemical make up of Titan's atmosphere was recorded as Huygens descended to the moon's surface, but it will take time to separate the hydrogen's signal from that of the other molecules. Another option would be to analyse acetylene levels in the atmosphere, which could be easier.
'I would guess that there would be a similar fall-off of acetylene if the microbes are eating it,' Dr McKay told New Scientist. The results of the pair's work will be published in the journal Icarus.