Lastly, we have known for many, many years that
Europa is in an interesting tidal situation with
Io and Ganymede.
The result of these tides, as you'll see in your homework,
is that Io, Europa, and Ganymede are constantly being
stretched and compressed through gravitational interactions
with each other and with Jupiter. One result of this
stretching is an increase in heating of the moons.
Io has the most, then Europa, and then Ganymede.