Four of Jupiter's moons, Europa, Io, Ganymede, and Callisto, are collectively known by which name?

There may be a liquid ocean 100 miles deep under the ice of Europa. That's twice the water of earth on a moon 1/4 its size. With 10B population coming, we better figure out how to get it.

I did not know this. But I remembered Galileo had seen four of Jupiter's moons with his telescope.

A very clever man!

Actually the conflict was that the Catholic Church believed the earth was the center of the universe and it did not revolve. He was under house arrest until his death