This absolutely dwarfs both the heat produced through radioactive decay and insolation.Jupiter’s moon Europa is believed to have a subsurface ocean deep beneath its frozen crust. Run the model, and you get about 0.6-1.6E14 W heat generated by this process, which is consistent with the observed heat loss from Io. The moon's tidal bulge stretches by a hundred meters between the apogee and perigee, despite the low eccentricity. If you do the math, the tidal forces on Io are twenty thousand times the tidal forces the Moon causes on the Earth (and the Moon is pretty massive as moons go). It's easy to underestimate just how massive Jupiter is. But consider that Io is mere 400kkm away from Jupiter, and Jupiter is rather. Yes, the eccentricity of Io isn't particularly high. If the other moons didn't exist, Io would be on a circular orbit much further away from Jupiter, and wouldn't be getting any appreciable tidal heating. There's an orbital resonance (with the other Galilean moons) that prevents Io's orbit from circularizing, and also prevents Io from migrating away from Jupiter. That sentence on wikipedia continues "from friction generated within Io's interior as it is pulled between Jupiter and the other Galilean moons". "How tidal heating in Io drives the Galilean orbital resonance locks." Nature 279.5716 (1979): 767-770. "Strong tidal dissipation in Io and Jupiter from astrometric observations," Nature 459.7249 (2009): 957-959. Io's orbit circularizes and Io's interior cools. At some point, the tidal stresses that lead to circularization dominate over the effects of Europa and Ganymede. Tidal stresses now become significant and Io's interior warms up. The resonance effects now begin to dominate, making Io's orbit become more eccentric. This reduces the impact of Jupiter's circularization effects on Io's orbit. Suppose Io's interior is cool and its eccentricity is very low. This has been hypothesized to lead to an interesting hysteresis loop (e.g., Yoder). These interactions tend to increase Io's eccentricity. However, Io is also in a 1:2:4 orbital resonance with Europa and Ganymede. Those tidal stresses normally would act to circularize Io's orbit about Jupiter, thereby reducing the tidal stresses. The fact of $e^2$ means that the tidal energy dissipation strongly depends on eccentricity. Io is a large moon (larger than our Moon) and it orbits fairly close to Jupiter.įinally, even though Io's eccentricity is small, it is not zero. The power of five on the mean motion and moon radius means that a large moon that orbits close to its parent planet will be subject to vastly more tidal stress than a small moon that orbits far from the parent planet. Io's volcanism is a sign of a moon with at least a partially molten interior. Compared to a moon with a solid interior, a moon with a partially molten interior will have a slightly higher value of $k_2$ and a significantly lower value of $Q$. The ratio $k_2/Q$ strongly depends on the makeup of the moon's interior. $e$ is the eccentricity of the moon's orbit.$G$ is the universal gravitational constant, and.$Q$ is the moon's tidal quality factor,.$k_2$ is the moon's second order tidal Love number,.$\dot E$ is the rate at which tidal energy dissipates,.claim that the global energy dissipation in a tidally-stressed moon is given by That Io is in an eccentric orbit rather than a circular orbit means that tidal stresses can and do build up. It is tidally locked in a mean motion sense of "tidally locked". How can Io be tidally heated while it is in tidal lock?
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