# Did this paper just argue that there is surely life on Titan?

I just read the popular press version of a new paper, and now I have a question about Titan.

Here are some quotes from the pop article:

A rocky, ocean-bearing planet with more than 0.1 percent methane in its atmosphere should be considered a potentially inhabited planet, the researchers say. And if the atmospheric methane reaches levels of 1 percent or more? In that case, “potentially” doesn’t cut it—such a world would “likely” be home to alien life.

...

Thus, methane and carbon dioxide together, unaccompanied by carbon monoxide, on a rocky, ocean-bearing world would best be interpreted as an airtight sign of anoxic life.

Titan's atmosphere
Stratosphere:
98.4% nitrogen
1.4% methane
0.2% hydrogen
Lower troposphere:
95.0% nitrogen
4.9% methane
-OR, depending on who you ask-
97% nitrogen
2.7% methane


The density of Titan is consistent with a body that is about 60% rock and 40% water.

There are trace amounts of other hydrocarbons, such as [...] carbon monoxide [...].

If I understand correctly, 'trace amounts' of CO is in line with the requirements stated in the Catling paper.

So, is Titan covered in microbes, or what? Since the article didn't mention Titan, I presume I missed something. What was it?

• I believe the paper was referring to "oceans" of water; Titan is far too cold for that. The temperature of Titan disqualifies it from the argument presented in the paper (not that it is impossible that there is life on Titan, either in sub-surface ocean or in some exotic cold-tolerant form on the surface). Jan 25 '18 at 16:33
• The underlying article refers to a planet whose atmosphere contains free oxygen, which alone might be a sign of life. (But there are non-biological sources of free oxygen. For example, a planet without life that is undergoing a runaway greenhouse or moist greenhouse will exhibit a strong oxygen signature, at least until its oceans evaporate/boil to nothingness.) Titan has close to zero free oxygen, so this paradigm doesn't apply. Jan 25 '18 at 16:57