The universe is chock-full of unanswered questions, as you know, but a lot of them have to do
with our very own stellar neighborhood.
For example: why does Saturn have rings?
It's one of the most common questions asked about our solar system, and while there is
no single agreed-upon answer, understanding Saturn's rings might begin with the fact that
it's not the only planet around here that has them.
Jupiter has three very faint rings, Neptune has five, and Uranus has thirteen.
So a better question might be: why do all of our gas giants have rings?
To answer that, let's start with an interesting little rule that celestial bodies tend to
abide by, know as the 'Roche limit'.
First identified by French astronomer Édouard Roche in the 1840s, this limit is the distance
at which objects in orbit around a planet tend to be torn apart by the planet's gravitation.
A planet pulls harder on the side of a satellite that's facing it, so if a satellite gets too
close the unevenness of that attraction will likely cause it to break up.
And that is apparently what happened to most of our gas giants, because with a few exceptions
their rings are almost always inside their Roche limits, while the moons are outside.
So in the case of Saturn's rings, one prevailing theory is that billions of years ago some
rogue wanderer, like a comet, got swept into orbit within Saturn's Roche limit and broke
apart.
Another model suggests that a moon that once orbited Saturn at a safe distance got smacked
by a celestial object into the danger zone, where it disintegrated.
By this logic, then, part of the reason why gas giants have rings might have to do with
their size: they're just so big that they're more likely to draw in passing objects.
But their distance from the sun is important too.
While the rings of Jupiter and Neptune are basically faint halos of dust, those around
Saturn and Uranus are bigger and made up of almost entirely water ice, along with the
volatile organic compounds that evaporate easily.
So in addition to forming around large planets with big Roche limits, rings might also form
more readily around planets where it's cold enough for the icy fragments of those crack-ups
to survive.
So you could say that Saturn's rings are just beautiful remnants of bad break-ups.
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