London, Nov 4 : A new study has indicated that the Cassini probe may have already collected data that could reveal the presence of life on Saturn's moon Enceladus, in the form of an underground ocean capable of sustaining life.
Researchers have been fascinated with Enceladus since July 2005, when Cassini revealed a dramatic plume of ice particles and water vapour shooting out from the moon's south pole.
The plume's origin is still being debated, but some models suggest the moon holds an ocean of liquid water beneath its surface. This ocean could be a potential habitat for extraterrestrial life.
Now, according to a report in New Scientist, a team led by Christopher McKay of NASA's Ames Research Center in Moffett Field, California, Cassini could offer up the first evidence that life exists or once existed on the 500 km-wide moon.
Though the probe was never designed to look for life, it could do so by studying organic chemicals such as methane in the plume, according to the team.
"If you think about what you need for life, you need water, energy, organic material, and you need nitrogen, and they're all coming out of the plume," McKay told New Scientist. "Here is a little world that seems to have it all," he added.
Life could take the form of methane-producing microbes, or methanogens, similar to those that have been seen buried under kilometres of ice in Greenland.
Cassini could potentially find evidence for such life by studying the relative abundances of methane and heavier organic chemicals, such as propane and acetylene.
So far, flybys of the plume suggest its chemical makeup is quite comet-like.
That hints that the moon's methane was created early on, perhaps in clouds of gas that predate the solar system.
"That doesn't mean there's not a biological signal hidden under the other stuff, but we don't have any evidence to suggest that is the case," said INMS lead scientist Hunter Waite of the Southwest Research Institute in San Antonio, Texas.
"It's not a clear-cut, hands-down winner for biology," McKay acknowledged.
To better understand what a biological signal on Enceladus might look like, McKay has reconfigured a chamber previously used to simulate conditions on Saturn's moon Titan to simulate non-biological ways of making methane and other organic molecules.
The signatures could help researchers interpret Cassini's results, according to McKay.
According to Waite, the best way to search for evidence of life may be to return to Enceladus with more sensitive instruments.