Right, and that’s part of the problem with drilling. Rock does weird things at those temperatures.
Mars has less geological activity than Earth–which is like saying Xenon is less reactive than Sodium–but I imagine it does still get hot down there. Earth gets a lot of its internal heat from the decay of heavy radioactive elements, and I imagine Mars has some of the same.
Wait, it’s liquid water. There’s a lot of pressure, though, which would raise the boiling point, but it can’t be that hot, right?