If so, does that mean that precisely because Titan is geologically dead (if that is the case), the atmosphere, the hydrocarbon lakes or other parts of the surface of Titan probably contain living organisms?
I'm asking because there has been quite a bit of speculation about the methane in Titan's atmosphere. Wikipedia writes this about Titan's methane:
So if there is really no cryovolcanism to explain the methane in Titan's atmosphere, is it likely then that the methane was made by living organsims?Energy from the Sun should have converted all traces of methane in Titan's atmosphere into more complex hydrocarbons within 50 million years—a short time compared to the age of the Solar System. This suggests that methane must be somehow replenished by a reservoir on or within Titan itself. That Titan's atmosphere contains over a thousand times more methane than carbon monoxide would appear to rule out significant contributions from cometary impacts, since comets are composed of more carbon monoxide than methane. That Titan might have accreted an atmosphere from the early Saturnian nebula at the time of formation also seems unlikely; in such a case, it ought to have atmospheric abundances similar to the solar nebula, including hydrogen and neon. Many astronomers have suggested that the ultimate origin for the methane in Titan's atmosphere is from within Titan itself, released via eruptions from cryovolcanoes. A possible biological origin for the methane has not been discounted (see below)
Mars, too, has some methane in its atmosphere, although in very small amounts. Wikipedia writes:
Methane has been detected in the Martian atmosphere with a mole fraction of about 30 ppb; it occurs in extended plumes, and the profiles imply that the methane was released from discrete regions. In northern midsummer, the principal plume contained 19,000 metric tons of methane, with an estimated source strength of 0.6 kilogram per second. The profiles suggest that there may be two local source regions, the first centered near 30° N, 260° W and the second near 0°, 310° W. It is estimated that Mars must produce 270 ton/year of methane.
The implied methane destruction lifetime may be as long as about 4 Earth years and as short as about 0.6 Earth years. This rapid turnover would indicate an active source of the gas on the planet. Volcanic activity, cometary impacts, and the presence of methanogenic microbial life forms are among possible sources. Methane could also be produced by a non-biological process called serpentinization involving water, carbon dioxide, and the mineral olivine, which is known to be common on Mars
I'm asking this because I have read a bit of speculation that methane is a good tracer of life on other planets. And the methane in the atmospheres of Mars and Titan, which are worlds that seem life-friendly for other reasons, has been cited as possible biomarkers there.
My question is how good methane is as a tracer of life. If, for example, NASA manages to build the kind of telescope that can detect and analyze atmospheres on planets in other solar systems, how should we react to the news that the atmosphere of such an exoplanet has been found to contain methane?