There’s a potential new wild card in our search for life on other planets.
Two teams of scientists reported last week that data from NASA's Cassini orbiter reveal unusual chemical activity on Saturn's giant moon Titan.
It's plausible, but far from definitive, that a primitive exotic form of life on Titan's frigid surface could be causing the strange results.
Earth organisms would barely last a few seconds before freezing solid on Titan's -300 degree Fahrenheit surface. But this could be tantalizing evidence for "cryo-life." It would be an utterly alien biology existing at very low temperatures where liquid methane and ethane are used in place of water as a solvent.
Confirmation of such an exotic life form would simply blow the doors off any doubt that life is a fundamental condition of the universe. Why? Because not only would we have evidence of a second genesis in the solar system, but a genesis that used a completely different chemical strategy under extreme conditions for assembling self-replicating matter.
Such an alien biology would dramatically underscore the emerging view that "life finds a way" — in this case through a completely different biochemical pathway. Such a discovery would be even more profound than finding carbon-based life on Mars.
The two puzzle pieces are (1) hydrogen molecules raining out of Titan's atmosphere disappear at the surface, and (2) acetylene that should also be raining down due to photochemical processes in the upper atmosphere is also missing from Titan's surface.
One explanation is that life on the surface is consuming the hydrogen (as we consume oxygen) and using the acetylene as an energy source. (Though methane is a byproduct of Earth microbes, methane-based life forms have never been identified on Earth.) Astrobiologist Chris McKay of NASA's Ames Research Center in Mountain View, Calif. first proposed this hypothesis for methane-based life on Titan in 2005.
While what is being observed could be due to biology, it could also be due to some unknown low- temperature, non-biological catalysis.
"This is almost as odd to imagine as an alien biology," McKay told me. "It would require some unknown mineral acting as the catalyst on Titan's surface that converts hydrogen molecules and acetylene back to methane."
Settling the mystery would require a Titan lander to conduct experiments on surface material. "We possibly could measure metabolism but (as with the Mars Viking experiments) there could be confusion between chemical reactions and biological metabolism," says McKay. "Detection of biomolecules would be easier and more definitive." This would require a gas chromatograph mass spectrometer (GCMS), as is being flown on upcoming Mars Science Laboratory and was flown on the twin Viking Mars landers, and ESA Huygens Titan lander (which carried a GCMS for atmospheric studies.)
"The distinction between microbial activity and a non-biological catalysis would be the accumulation of complex and non-equilibrium organic molecules, the alien equivalent of ATP and Ribisco," says McKay.
If exotic alien life were someday confirmed on Titan, it would further dilute the idea of a precise "habitable zone" around stars. Various manifestations of life could evolve under a wide range of temperature and chemical environments. This would unfold on a variety of moons and planets throughout a planetary system.
True, intelligent life might only have its best shot in a habitable zone supporting carbon-based biology. And, detection of exotic astrobiology across interstellar distances is probably impossible without in situ experiments. Therefore, Titan could turn out to be our first and perhaps only example of life as we don't know it.
Image credit: NASA