New experiments suggest gravitational pull may be generating more heat than previously thought. Bill Condie reports. Constant gravitational pressures on the icy surface of Jupiter's moon Europa generate much more heat than previously thought, which may force a rethink about the chemistry of the liquid water ocean below the surface. Scientists at Brown and Columbia universities were encouraged to investigate the phenomenon because of what was happening to the surface of the moon. "There was clearly some sort of tectonic activity – things moving around and cracking," says Columbia's Christine McCarthy, who led the new research as a graduate student at Brown. "There were also places on Europa that look like melt-through or mushy ice." The only way to create enough heat to have this effect apart from exposure to the Sun was by the tidal compression caused by Jupiter's huge gravitational field. It was already understood that tidal pressures as the moon orbits Jupiter gently heats Europa