Ring around a planet

allan_35 · Dec 20, 2004

Hello, I am writing a story and I want to get some of the explanation down correctly. I explained the action as far as I could in the rough draft but I pretty sure that I was a bit off base as I just wanted to depict the act as it appeared to people living on the planet. I explained it as a moon that terrestial scientists had determined was approaching the planet closer each year. That the moon, from the ground, seemed to glow from within (volcanic problems due to strengthening gravity), and one day seemed to be torn apart. Over the next few days the remnents seem to stretch across the sky until finally it stretched across the entire sky. I think I put this in the time from of just a few years. I then went on to describe the "falling stars" that occurred every few seconds or so. All of them flashing in the same general direction. How far off am I? Is the time line close? Would volcanic action be visible from the surface of the planet itself? If you wouldn't mind helping me out on this, you can either reply on this board or email me at allan_35@yahoo.com. Thank you in advance.

Maddad · Dec 20, 2004

It's an interesting idea, allan. Welcome to SDC, by the way. I don't see any problems with it that would make it unworkable. It'll be interesting to see if someone else can find something. Good first post.

nexium · Dec 21, 2004

The only possible problem, I see is Earth's moon is presently moving away, but moving closer is likely possible by some mechanism. Neil

allan_35 · Dec 21, 2004

This takes place in a fictional place. I am familiar with the drifting of our moon, in this place I am attempting to conjure to imagination started with two moons, one with an atmosphere and bodies of water that can be seen from the surface of the planet, but due to the medieval nature of the planet no advanced science exists to either get there or to probe it with any certainty. The other moon isn't there at the time of the story line, only its remnants. I am looking for a plausible explanation to depict the breakup of a moon drawn in to close to the planet and the resultant breakup to allow for a ring being established around it. I think I read somewhere that all of our gas giants had moons at one time that have resulted in the rings there today. Also explained (perhaps hypothetically) was the fact that the rings themselves are doomed to fall to the power of the planet’s gravity. I figured that since the moon wasn’t revolving as it orbited the planet, that there wasn’t any internal volcanic action (I am guessing that this may be the reason that there exists no volcanic action in our own moon), yet that is negated by the sheer force of the gravitational forces working on the moon as it succumbed to the gravity well of the planet itself. The main thing I am looking for, assuming I am correct in my explanation of a deteriorating orbit that results in a ring, is the timeline that one would hypothesize in such a scenario. And I guess that will mean that I have (or should) annotate somewhere in my storyline that the moon with the atmosphere does indeed spin in its orbit around the planet. This plays a very minor point in the story; however, it is not without reason that I may introduce something further in the story that will bring the moon into the story itself.

qzzq · Dec 21, 2004

I figured that since the moon wasn’t revolving as it orbited the planet... Hmmm, all moons, at least after a while, become tidally locked to the planet they orbit. This means they always face that planet with the same side; a side that kind of bulges out through the gravitational pull of the planet. In order to be tidally locked, a moon must revolve around its axis. Depending on how large the two orbiting moons are compared to the mass of the host planet, the disappearance of one moon is likely to affect the relation between the planet and the remaining moon as well. ( EDIT; the moon turns into a ring, so its mass doesn't disappeare of course; it merges with that of the planet, so the remaining moon will become subject of a greater gravitational pull ) Your story may work better if the moon that is falling apart, is a passing object ( asteroid or comet ) caught by the planet's gravity; a young, new moon. Same lightshow probably. Just a suggestion of course. A moon in orbit around Jupiter falling apart wouldn't have much effect on Jupiter, because it's so massive. Now if something were to happen to our moon, the effects would be highly noticeable, desastrous even, because Earth doesn't outweigh its moon as Jupiter does to, say, Europa. So if the moon turning ring in your story is too massive in relation to the planet, your planet's inhabitants are in really big trouble, which is not per se bad for the story of course. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> *** </div>

heyscottie · Dec 22, 2004

But how close would a moon like ours have to get to a planet like ours before it is torn apart? It may need to be pretty close. You *could* let your destroyed moon be a large loosely bound captured comet. This would give you more reason to have it drifting inward, due to its inherently unstable orbit (the other moon could perturb it inwards, too), and would allow it to break apart easier.

qzzq · Dec 22, 2004

Yeah, a comet would probably work best. The tidal stress caused by our moon's gravity is the main reason Earth's core remains liquid, which in turn provides us with a magnetic field. So we need it. Badly. If the moon some day would start to move closer to Earth, increased vulcanic activity, earthquakes and flooding caused by a more extreme tide would be among the first noticeable signs of our imminent destruction. You need a pretty big comet to do the same. Drifting moons are a very dangerous business. But I doubt a moon would break up that easily. It would pretty much impact in one piece. Now there is an extinction level event. As for the ring: a comet would have to be really massive to create a visible ring of debry around a planet. Colliding moons may cause a more spectacular sight. <div class="Discussion_UserSignature"> *** </div>

mcbethcg · Dec 22, 2004

The mechanism that would cause the breakup is refered to as the Roche limit. Explained here: http://curriculum.calstatela.edu/courses/builders/lessons/less/les1/moons/roche.html The Earths moon is slowly moving away because the earths rotation is transfered to it through gravitational effects. This also causes our rotation to slow down. In your fictional world, the moon would be able to slow down in its orbit and move closer if it started out in an orbit that was in the opposite direction as the rotation of the planet. The likelihood of a planetary system forming in such a way is remote, but it might be possible if the moon started out as a rogue planet and was captured.

bobvanx · Dec 22, 2004

<blockquote>In reply to:<hr />The tidal stress caused by our moon's gravity is the main reason Earth's core remains liquid,<hr /></blockquote>...um, most scientists think it's leftover heat from the Earth's formation along with radioactive decay, that keeps the Earth's interior molten. There's a bunch of debate about waht contribution the Moon has to keeping our planet flexing. There's a consensus that the Moon stabilizes the Earth's rotational axis, but the idea that the moon has enough tidal energy to impart internal heating to Earth is ...less commmon.

alkalin · Dec 22, 2004

“The Earths moon is slowly moving away because the earths rotation is transfered to it through gravitational effects. This also causes our rotation to slow down. “ These are tidal effects due to Earth’s rotation that pulls maximum tides ahead of the moon’s position, causing a slight forward gravity vector that causes the moon to gain speed, and hence move further away. And as you indicate these effects are also slowing the Earth’s rotation. What happens when some day the Earth rotates at exactly the same period as the revolution of the moon? The tidal feedback to the moon is lost, and it will not be pulled faster. Because the moon’s orbit is not perfectly circular, there will likely be in fact some gradual loss of the moon’s speed. and it slowly over much time gets a lot closer, until the Roche limit is reached, at which time--fireworks.

qzzq · Dec 27, 2004

bobvanx posted: --There's a consensus that the Moon stabilizes the Earth's rotational axis, but the idea that the moon has enough tidal energy to impart internal heating to Earth is ...less commmon. Hmm, I always assumed this was the case, but I did some googling and you are right; I couldn't find one link to support my claim. Thanks for the correction. <div class="Discussion_UserSignature"> *** </div>

iron_sun_254 · Dec 27, 2004

In your fictional world, the moon would be able to slow down in its orbit and move closer if it started out in an orbit that was in the opposite direction as the rotation of the planet. The likelihood of a planetary system forming in such a way is remote, but it might be possible if the moon started out as a rogue planet and was captured. The effect would also occur if the moon orbited faster than the rotation period of the planet. The moon would then transfer some of it's energy to the planet causing the planet to spin faster and it to drop into a lower orbit.

nexium · Dec 27, 2004

There seems to be some contradictions amoung mainstream astronomers, so your story is likely credible, even if it violates some opinions. That Earth's moon is moving away is established by actual measurements. The problem is why it is moving away. If the moon slows, it's orbit should become more eliptical and/or move farther from Earth. This is evidenced by low Earth orbit about 18,000 MPH, Geo orbit about 3400 MPH and the moon's average speed 2500 MPH. If the moon moved to GEO orbit it would be near the roache limit and would disintigrate if hit by a large impactor. At least one of the planets found in other solar systems is closer than the roche limit, so perhaps Mr. Roche's assumptions were flawed or the data concerning the planets in other solar systems is in error. It occurs to me that the adhesion and cohession of the body has considerable baring on when it will disintigrate into a ring. My guess is an atmosphere or no, has little baring on weather the body recedes or moves closer. The faster rotation of the less massive body may however cause the orbital radius to shorten. The equator of our sun rotates faster than any of the planet's equators rotate = the planetary orbits are getting longer and slower? Please refute, embellish and/or comment. Neil

nexium · Dec 27, 2004

I like multiple causes for most everthing. Most astronomers agree the interior of Io is hot because it relatively close to Jupiter, which has about one million times the mass of Earth. If so, reasonably perhaps 1% of the internal heat of our Moon (thought to be warm rather than hot) is due to Earth tides and Earth's interior is heated slightly by by moon tide and sun tide. Likely radioactive decay warms all bodies slightly. After 4.6 billion years, I would expect fosil heat to be the least of the three. I suspect we will eventually discover a 4 th source of heat, perhaps some miniture black holes orbiting the core of Earth? Neil

Saiph · Dec 28, 2004

Mcbethcg has it right. If the moon is orbiting opposite the planets rotation, it will become closer. If the moon and planet are the same sizes as ours (or roughtly) the moon will disrupt at ~3 earth radii due to tidal forces. The ring will be created in days however, maybe weeks. There will be a relatively constant stream of debri entering the atmosphere, in the same general direction, as you've stated. Nexium: One of the primary sources of heat for the earth's core is radioactive decay. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

allan_35 · Jan 5, 2005

Hey you all, Thanks for the input. I really like the idea of the comet, only it would be such a pain to pull all the cobwebs from the story line concerning a moon that broke apart and replacing it with a comet. I think I will extend the time of the break up from a couple of days to around a week, perhaps a week and a half.

allan_35 · Apr 7, 2005

Hello All, I wanted to thank you all for your help in the timeline involved with the ringed planet idea. I sent my manuscript in to American Publisher and they accepted the story. I imagine that the book will be finished within the year under the title "Elixir of Power". Thanks again for the support. Allan

CalliArcale · Apr 7, 2005

Sweet! Congratulations, allan_35! Let us know when the book gets released, so we can all go out and buy copies to support a fellow SDCer with cool concepts. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

Ring around a planet

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