Europa is interesting enough without throwing in a new theory about energy sources. But Robert Tyler (University of Washington) has been studying the possibilities in Europan tides, using computer simulations that offer a different way of getting energy out of this icy world. We’ve speculated that Europa experiences enough tidal flex from Jupiter to create possible energy sources for life. What Tyler is saying is that the moon may experience not just internal pressures but large waves pushing through the submerged ocean. These waves, of course, could be a way of distributing heat and dissipating tidal energies.
This being the case, the assumption that energy may come from flexing at the core, as well as pressures on the oceanic ice sheets, has to be supplanted by a different view:
“If my work is correct then the heat source for Europa’s ocean is the ocean itself rather than what’s above or below it,” Tyler says. “And we must form a new vision of the ocean habitat that involves strong ocean flow rather than the previously assumed sluggish flows.”
Causing the waves is obliquity, the axial tilt of the moon in relation to its orbital plane, which results in a tidal force not previously considered in Europan terms. Earth’s axial tilt is 23 degrees. Europa’s hasn’t been measured, but Tyler believes that even at minimum values, it should be sufficient to produce significant heating. If obliquity does cause waves in an ocean we’ve long assumed as calm, then we have another way of explaining how Europa’s ocean manages to stay liquid. After all, the surface of this world is extremely cold — minus 160 degrees Celsius — while any sources of heat produced by radioactive decay seem meager.
Obliquity could be highly significant in the overall energy picture. From the paper:
“…the minimum kinetic energy of the flow associated with this resonance (7.3 X 1018 J) is two thousand times larger than that of the flow excited by the dominant tidal forces, and dissipation of this energy seems large enough to be a primary ocean heat source.
Tyler’s work gives us another take on the energy possibilities on Europa, and by extension on other moons suspected to have oceans, such as Ganymede and Callisto. And that has to play well with astrobiologists speculating on life’s development under distant ice. The paper is Tyler, “Strong ocean tidal flow and heating on moons of the outer planets,” Nature 456 (11 December 2008), pp. 770-772 (abstract).