Jupiter’s moons could keep each other warm by raising tidal waves
It takes a certain amount of heat to keep an ocean wet. For Jupiter’s largest moons, a new analysis suggests a surprising source for some of that heat: each other. Three of the gas giant’s four largest moons, Ganymede, Callisto and Europa, are thought to harbor oceans of liquid water beneath their icy shells (SN: 5/14/18). The fourth, the volcanic moon Io, may contain an inner magma ocean (SN: 8/6/14). One of the primary explanations for how these small worlds stay warm enough to harbor liquid water or magma is gravitational kneading, or tidal forces, from their giant planetary host. Jupiter’s huge mass stretches and squishes the moons as they orbit, which creates friction and generates heat. But no studies had seriously considered how much heat the moons could get from gravitationally squishing each other. “Because [the moons are] so much smaller than Jupiter, you’d think basically the tides raised by Io on Europa...