NASA - National Aeronautics and Space Administration

QUESTION:
How can methane be on Titan, as recently speculated by scientists?

My problem is that I have always believed that methane was produced by bacteria feeding on vegetable matter in a non-oxygen environment, like at the bottom of a lake or deep within the bowels of our Earth. But if methane exists on Titan, it must have been produced by some method other than bacterial action. So I think that is my question -- just what other methods are there that produce methane?

ANSWER:
Saturn's largest moon, Titan.
Methane is produced biologically, but it also is produced by many non-biological processes. The atmospheres of Jupiter and Saturn are composed predominately of H₂ (hydrogen). In such an atmosphere, all the C (carbon) is converted to CH₄ (methane). In our atmosphere (O₂ rich), the stable form of C is CO₂.

There also is methane in comets.

We are not sure where the methane on Titan came from. It could have come from the same material that forms Saturn if Titan formed as part of the Saturn system. Or it could have come in from comets.

Note that comets would also bring methane to Earth, but here it would react to become CO₂.

Chris McKay
Space Science and Astrobiology Division
NASA Ames Research Center, Moffett Field, Calif.


NASA Ames Research Center, Moffett Field, CA