Of course the answer is 42. Which makes sense. Nothing else really does make sense when we talk about life in the Universe. This Universe, or one of the possible Multiverses.
Let's be clear: I'm no specialist. An online course on astrobiology does not qualify me to speak about extremophiles, or discuss about where and how to find them within our solar system.
Yet, I like to think about the existence of sentient beings other than ourselves and our fellows in the animal kingdom as an obvious fact of ... life.
But sentient beings does not mean "things" that see in the visible spectrum of light, or even that see at all. In caves animals loose the ability to see, since they do not need to see a light that does not exist. And I assume that beings which would have evolved on the Moon, if that would have been the case, would not have used air waves to communicate, since air is not an option on the Moon.
Now, those are of course simplified cases, but considering how quickly our body adapts to different conditions, say, microgravity, by loosing fluids or calcium, or reducing muscle mass, we can only assume that beings growing in a different world would adapt to the physical parameters of that world. Therefore developing a need to use the most appropriate senses for that world.
Now, there is a chance that some of those beings may have developed some ways to sense portions of their environment that we share: like x- or gamma- rays. Unless they went for a more local adaptation, and then who knows, what beings living in the core of stars may be able to sense.
For them, beings like us, living in the cold of a planet surface would be real extremophiles, don't you think?
