For all that he'd like to think that the concepts of day and night were universal, there's little denying that neither are something that would be naturally occurring underground. Whether or not the Praxians had arranged to make something that would at least approximate the solar cycle is something that he can't answer (and still wishes he could) but he supposes that at least the earliest Praxians must have remembered life on the surface if nothing else. How well that will have translated into the map itself... well, that is rather the question at hand, isn't it?

"A wealth of information, perhaps?"

It's a stab in the dark, yes. But it's not like everything else so far hasn't been. And what's one more, if it actually gets them closer to what they're looking for, in the long run?