Europa floats in front of Jupiter. NASA / JPL-Caltech Floating in space about 390 million miles from Earth is a small moon of Jupiter named Europa.

The most astounding fact about Europa is the watery ocean sloshing beneath the moon's icy, outer crust.

Despite its size, which is four times smaller than Earth, Europa is thought by scientists to harbor even more water than all of Earth’s oceans combined.

For example, if you could form a giant sphere with all of the water on Europa, that sphere would be about 1,090 miles across — 300 miles wider than if you did the same thing with all of the water on Earth.

That’s a lot of water for such a tiny moon, and it makes for a very deep and vast potential habitat for alien life.

How deep? Scientists estimate that some parts of Europa's ocean could reach over 100 miles beneath the thick outer surface. That's 16 times deeper than the deepest place on Earth, at the bottom of the Mariana Trench in the western Pacific.

To give you an idea of this, the folks who run the YouTube channel “5 hours ahead” have made this awesome short GIF that's a struggle to stop watching: