I'm a physicist, so I actually enjoy doing these kinds of calculations over my morning coffee. Hope that's not more detail than you were looking for. Io orbits Jupiter in an orbit that is not quite circular and, like our Moon always faces the same side of Earth, so does the same. This also causes the tidal bulges to move around, dissipating energy in Io and producing internal heating. Io is volcanically active due to a process called tidal heating. Also, the eccentric orbit prevents perfect tidal locking, so Io experiences libration just like the Moon does- from Jupiter's view, the satellite appears to wobble a bit. Because the orbit is eccentric, the tidal forces raise and lower tidal bulges just because the distance from Jupiter is changing- even without rotation of the satellite itself with respect to Jupiter. These other moons have prevented Io's orbit from becoming perfectly circular. But Io isn't orbiting Jupiter in isolation Europa and Ganymede in particular influence its orbit. If the tidal locking were perfect, there would be no heating of Io's interior by the tide, since the bulges would always be in the same location. Io is nearly tidally locked to Jupiter, meaning it always keeps the same face towards the planet. But the tidal force between the two is a whopping 5.48e20 N, 83 times higher than the tidal force exerted on the Earth by the Moon.īut there is one more thing to consider. So we see that even though the force of gravity between the Earth and Sun is much larger than between the Earth and Moon, the tidal force on the Earth is still greater from the Moon than the Sun.Ĭonsidering Jupiter-Io, the gravitational force is 6.35e22 N, similar to the gravitational force between the Earth and Sun. In the case of the Earth-Moon, you get a tidal force of 6.58e18 N, and in the case of the Earth-Sun, 2.98e18 N. However, in calculating the tidal force, you need to multiply this by 2r/R, where r is the radius of the body you are calculating the force on, and R is the distance between the two bodies. The force of gravity between the Earth and Moon is 1.98e20 N, and the force of gravity between the Earth and Sun is 3.52e22 N. In other words, we see a lunar tide on Earth because one side of the planet is significantly closer to the Moon than the other side, and therefore each side experiences a different gravitational force. Tides are not determined just by the gravitational force, but by the gradient of that force. What is the force on Io which creates all the activity? Eris wrote:I have recently read that the gravitational force between Earth and Moon is something like 2 x 10^20, and we get tides.
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