Mars, Moon, Earth, comet 67P. So far we're at 1/4 chance to have life on a celestial body.
Now THIS is interesting. Molecular Oxygen, aka O2, is a strange beast. I'm not sure I get the whole picture, but O2 is not a stable molecule over long periods of time. Oxygen likes to be paired with something, and that something is more often than not Hydrogen to for OH which will bind with something like Carbon or Nitrogen, or make water, H2O. UV light breaks up the bonds in O2, and one of the ideas of looking for life on exoplanets is that if there is a significant amount of O2 in the atmosphere of a plant, something has to be producing it; that something on earth is life.
This is not saying at all that there is life on this comet, that is very unlikely, but it does raise the question of where this O2 is coming from? It is being replaced by a chemical process in the comet? This is one of those discoveries that leaves more questions than before. One of the points they make talking about this discovery is that it was thought that if you had Methane and O2 together, this was the markings of some sort of biological activity. Now, maybe that has to be reevaluated.
If we find O2 on say Europa or Enceladus, then you start to get excited. Everywhere we find liquid water on earth we find life. My hope is that we find something alive on either moon that is completely different from earth in my lifetime.