I know it can't be water due to temperatures, so just what is the liquid in the hive tunnels?

Well there is likely some kind of atmosphere on the Moon now because the enemies seem to exist on its surface just fine (and it's likely that they have to breath). So I think we can assume some serious teraforming went on in the past, though there isn't too much evidence to support that.

Though the only evidence for this is in the opening cinematic where upon the Travelers arrival it started raining on the moon. It is otherwise quite dead. Maybe we can blame the hive for that?

But yeah, it definitely seems like the Moon has some sort of atmosphere now. Possibly done by the Hive, since the Golden Age corpses still use astrosuits.

I knew Jeopardy wasn't my game :-)

I'd like to argue about the moon having any atmosphere (I can logic out Mars due to the Traveler either restarting the core and adding additional metal and uranium via space magic or the implantation of extremely powerful magnets at the poles) but the lack of low-G and fact that the corpses inside the suit are skeletons (not mummified, but skeletons) doesn't give me much to argue about.

Think about it, just... just think about it for a long moment.

Actually, Zack said what I was gonna.

Also, in all seriousness, Vincent Price.

I wonder how wacky our tides are, now that the Moon is a lot denser. Maybe that's why Old Russia is all dried up, tide must be on the other side.

Considering that the Mediterranean dries up every few centuries (XKCD did a wonderful comic about this) I don't really know if the tides are affected based on the evidence we've seen. (That and areas such as the Russian shipyards exist in real life. Including Russia, if memory serves me correctly.) It could be a mysterious localized gravity manipulation rather than an adjustment of density. With how much space magic is thrown about, I can't say for sure one way or the other, but that's my best guess.

I mean, seriously. The Traveler doesn't seem to create any havoc on the local weather patterns for crying out loud! MST3K Mantra in full effect. (It doesn't stop me from tying to logic up actual pseudo-scientific solutions that fit the evidence we see, though!)

One supporting basis for my presumption is that if the moon were dense enough to have ~1 G, then it wouldn't stay in orbit for long. At that distance, Terra would begin to morph and stretch, as would Luna. They'd be drawn towards each other rather rapidly, rather quickly causing a rather catastrophic collision that might very well melt the surface of the Earth all the way to the mantle. They would fuse into one, with some ejection being formed, that would eventually form into a new moon.

Funny fact: It's believed that THIS HAS HAPPENED TO EARTH BEFORE. Sweet dreams!

THE DARKNESS THE DARKNESS!

Seriously - Do you not see the hive crawling out of it as a spawn?

Valid point made. I'd forgotten about that. We should ask Eris what this gunk is.

No, Eris. No, he's dead. We killed him last night. What we'd... No, I... Listen, we... Eris, please. Eris. ERIS! USEFUL INFORMATION PLEASE! I give up.