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Saturn's Rings Formed From Large Moon Destruction
Matt_dk writes "The formation of Saturn's rings has been one of the classical if not eternal questions in astronomy. But one researcher has provided a provocative new theory to answer that question. Robin Canup from the Southwest Research Institute has uncovered evidence that the rings came from a large, Titan-sized moon that was destroyed as it spiraled into a young Saturn."
It has a nice "ring" to it? Seriously? Be ashamed.
I think the article's content is more along the lines of "this new theory explains how Saturn's rings were formed, with their particular composition, while also explaining the other nearly-pure ice moons in the vicinity". The theory in the article is a little more comprehensive than "Saturn's rings were caused by a collision" (even though the summary was lacking information and seemed to imply that... go figure).
God liked it, so he put a ring on it.
We always see the same side of the moon because of tidal locking. It doesn't have anything to do with how the moon formed except in that the impact hypothesis puts the new moon close enough to the Earth that it became tidally locked fairly quickly, but that isn't unique to the impact hypothesis. In very basic terms it works like this:
1) Tides cause bulges on one or both bodies
2) The material that the bodies are made of resists that bulge so the bulge is never precisely where it it 'should' be gravitationally speaking. If the body rotates slower than it revolves the bulge will be behind, faster than it revolves and the bulge will be ahead. Let's say the bulge is ahead in this example.
3) The orbiting body (relative to the tidal bulge) is slightly more attracted to the bulge, since it is slightly closer than the rest of the planet. Since the bulge is ahead this pulls the bulge back (causing the bulging body to slow its rotational speed) and pulls the orbiting body as a whole forward (causing it to increase it's revolution speed).
In the Earth/Moon system, this has locked the moon's rotation rate to it's revolution rate. The same isn't (yet) true for the earth, if you stand on the moon you will see all sides of the Earth. However, that is very, very slowly changing. Each trip around the planet, the moon steals some of the Earth's rotational energy and turns it into orbital energy, raising the orbit of the moon a tiny bit and lengthening the day a tiny bit.
Well, I read all the comments so far and nobody has discussed the actual new parts of the model. The novelty is that the destroyed moon is assumed to be differentiated (The heavy metal and rock fall to the core and the light ices stay on the surface.) and Saturn was in its very early stages, when it was hot and its atmosphere greatly distended. This means that as the moon spirals in toward Saturn, its icy mantle gets stripped off by tidal forces first. That makes a vast disk of icy material from which the inner icy moons and the ring system are formed. Since the denser rocky material at the core of the moon is less affected by tidal forces, it impacts the extended atmosphere of Saturn and gets swallowed up before it has a chance to contribute to the disk. This explains the composition of the rings and moons better than previous models.
The point is not that it was a moon. There was no collision. Takeaway point if tl;dr:
The rings were formed by tidal disruption of a moon with an icy mantle and a rocky core.