And although Io’s atmosphere is one of the thickest of all the moons in the solar system, it’s still relatively thin-Earth’s atmosphere is around 200 million times denser. However, for all its tidal heating, the surface of Io is around –143 ☌. Io is the most volcanically active moon in our solar system, with plumes of material reaching up to 300 kilometres from the surface, spewing out masses of what is possibly either silicate rock or sulfur-rich material into space. The uneven gravitational pull causes the moon to bulge, then bounce back, causing friction inside Io’s interior, driving its intense volcanic activity. As Io orbits around Jupiter, its oval-shaped orbit means that Jupiter’s extremely strong gravitational pull is stronger at some times during the orbital path, and weaker at others. Gravitational pulls from Jupiter’s next two moons, Europa and Ganymede, have tugged Io’s orbit into an oval shape. Io’s vigorous dynamic activity comes from something called ‘tidal flexing’. Io is the closest moon to Jupiter, and a veritable hotspot of volcanic activity. Image adapted from: NASA (used with permission) Io An artist’s impression of the Galilean moons of Jupiter. Nevertheless, they are all tantalising prospects for finding life beyond Earth. All four moons are extremely cold, and all have thin atmospheres. Jupiter's large Galilean satellites experience this kind of heating - enough to produce extensive volcanism on Io and possibly create liquid-water oceans beneath the surface of Europa.Although some have speculated that life may be possible within the atmosphere of Jupiter itself, more likely candidates are the four icy Galilean moons around it. The more elliptical the orbit, the stronger the tidal heating. This continual flexing of the satellite creates heat through internal friction, in the same way, that if you flex a tennis ball enough times it becomes warm.
As it moves away from the planet the stress is partly released and the body relaxes back toward a more spherical shape. In that case, the satellite comes closer to the planet during one part of its orbit and there it's subjected to strong stretching forces. In fact, tidal forces can heat the interior of a satellite in an elliptical orbit. These rings are the remnants of bodies that were broken up by tidal forces.Įven when there's no water to respond to tidal forces, the solid mass of a planet feels the stress caused by these forces. That's why we don't see satellites orbiting too close to planets - instead, we see ring systems within a certain distance of the planet. Within a certain distance called the Roche limit, stretching forces can break it apart. So the closer an object comes to a planet, the more it's stretched. The closer two objects are in space, the stronger the gravity between them, and the stronger the tidal force. If a satellite (or a passing body) comes very close to a planet, the tidal forces can be destructive. Instead, it's in a 3:2 resonance - in other words, Mercury's day is two-thirds as long as its year.Ĭloser to the Roche limit the body (an exoplanet) is deformed by tidal forces. Mercury's eccentric orbit prevents it from being in a 1:1 spin-orbit resonance.
Pluto and Charon are tidally locked to each other. Examples of this are common in our Solar System.
Another way of saying this is that the Moon is in a 1:1 spin-orbit resonance - the ratio of its rotational (spin) period to its orbital period is 1 to 1. We always see the same face of the Moon from the Earth because the Moon's rotation period is the same as the time it takes to complete one orbit around the Earth. This is why most satellites, like the Moon, face toward their planet - they are "tidally locked" in that orientation.
Just as the Earth's rotation is slowing due to the Moon's tidal force on it, the Moon's rotation has slowed until it is locked into this position. The same tidal force that stretches a satellite also tends to slow its rotation until the longest axis of the satellite lines up with the planet. (The Moon is shown in polar view, and is not drawn to scale.) If the Moon didn't spin at all, then it would alternately show its near and far sides to the Earth while moving around our planet in orbit, as shown in the figure on the right. Except for libration effects, this results in it keeping the same face turned towards the Earth, as seen in the figure on the left. Tidal locking results in the Moon rotating about its axis in about the same time it takes to orbit the Earth.
0 kommentar(er)
