[neilep (OP)]

Dearest Asteroid-Beltologists,

As a sheepy I of course luff the asteroid belt. It's my all time favourite bunch of rocks and things that reside between Mars and Jupiter.

Look here it is


AsteriodBelt.jpg (16.78 kB . 300x300 - viewed 20904 times)
Being Delivered Next Tuesday



Please do not confuse it though with a Haemorrhoid Belt thusly:


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A Haemorrhoid Belt Earlier Today


As ewe know, planets are made when lots of rocks and stuff come together because of a magic force called gravity. Well, could that happen to the asteroid belt ?...and if not..why not ?..after all...it's made up from lots of big asteroids and small ones too..so surely the big ones attract the smaller ones yes ? and so on and so forth to make a new planet..yayyyyy !!

whajafink ?


hugs & shmishes


mwah mwah mwah !!



Neil
If I was travelling at speed in the belt asteroid
It's the rocky things that I'd want to avoid
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[Soul Surfer]

No they cannot form a planet for two reasons.  Firstly,  there just isn't enough stuff in the asteroid belt to form a decent sized planet.  and Secondly because the asteroids are smallish and "next door" to the giant planet Jupiter.  The orbits are quite badly disturbed in the long term by Jupiter and this creates zones of avoidance that are close to resonance ratios and to coalesce into one planet asteroid would have to cross these zones of avoidance

[neilep (OP)]

No they cannot form a planet for two reasons.  Firstly,  there just isn't enough stuff in the asteroid belt to form a decent sized planet.  and Secondly because the asteroids are smallish and "next door" to the giant planet Jupiter.  The orbits are quite badly disturbed in the long term by Jupiter and this creates zones of avoidance that are close to resonance ratios and to coalesce into one planet asteroid would have to cross these zones of avoidance

Brillinat ...thank ewe very much Ian..

erhhmm....sorry to ask ewe this further but could ewe please explain what a ' zone of avoidance' is and what a ' resonance ratio ' is too ?

Thanking ewe muchly.

[Soul Surfer]

the period of the orbit of mars about two earth years  The period of the orbit of Jupiter is about twelve years.  Most of the asteroids have orbits in the range three to seven years  if an asteroid had an orbital period of say four or six years it would come close to Jupiter regularly and be disturbed by it.  This is precisely what is found  they are called the Kirkwood gaps in the asteroid belt.  similar gaps are also seen at ratios of  5:2 and 2:3 of Jupiter's period  these sorts of relationships are called resonances

A similar effect can be seen in the rings of Saturn  the big gap called the Cassini division corresponds to an orbital period resonance with the orbit of Saturn's biggest moon Titan

[chris]

This thread reminded me of an interview with did with David Minton on his work on Kirkwood Gaps; here's a transcript.

Between Mars and Jupiter is a very large field of orbiting debris, but it contains holes called Kirkwood Gaps where the material that would have sat there has been dislodged by the gravity of giant planets like Jupiter. But when a research duo in the US ran a computer simulation they found more holes than the present theory could account for, and what these empty spaces are actually revealing is how the planets migrated to their present positions when the solar system was very young. Here’s David Minton.

David Minton: The asteroid belt is basically a belt of loose debris and rocks that orbits the sun between the orbits of Mars and Jupiter. What it is, is the leftovers of planet formation, it was a region that, because of Jupiter’s gravity, was too unstable to form planets so all the stuff that went into making a planet elsewhere in the solar system sort of got kicked out and that’s one unstable region and we’re sort of left with the debris at a place where planet formation never really got past a certain stage.

Chris Smith: And is all the debris in that region just uniformly scattered through space, or are there hot spots where there’s more of it and cold spots where there’s less of it?

David Minton: In some ways it’s almost uniformly scattered but there are these gaps, and these gaps were actually noticed about 150 years ago by a scientist and astronomer named Daniel Kirkwood and since then named the Kirkwood Gaps. And they are specific locations where there is, what is called, a resonance with Jupiter.

For instance, there’s a two to one Kirkwood Gap, which is a place where, if you stuck an asteroid there, it would orbit the sun two times exactly for every one time Jupiter orbited, and because of this resonance it’s a very unstable orbit and it’s a very unstable place so an asteroid doesn’t last in that particular place for very long. And so these specific locations, and there are a multiple of them for different resonance locations, get emptied out of asteroids and so there are currently gaps. What we wanted to ask was: how much of the asteroid belt is shaped by the gravity of Jupiter and Saturn?

Chris Smith: So how are you actually doing that?

David Minton: Well it turned out to be a trickier problem than we first imagined, and took a whole lot of computing power because what we ended up doing was we sort of built a computer simulated solar system and in our computer simulation we filled up the asteroid belt region, the sort of region stretching between Mars and Jupiter, with a whole bunch of computer asteroids and then just let it go, let these computer planets orbit the sun and let these computer asteroids orbit and just let the whole belt be shaped by the gravity of the solar system. And after four billion computer years we were left with an asteroid belt that looked a little bit different than the asteroid belt we see today. There are places specifically around some of these gaps, around these Kirkwood Gaps, where the sunward facing side of the Kirkwood Gap had lots of asteroids but the Jupiter-facing side of the Kirkwood Gap seemed to be depleted in asteroids, like there weren’t as many there as there could have been.

Chris Smith: So what do you think’s going on, how would you explain those missing lumps?

David Minton: Well the explanation that we’ve come up with is that this is a record of this migration of the giant planets.

Chris Smith: So are you saying then that the planet configurations we see today aren’t where the planets formed, they didn’t form in that situation, they started somewhere else and they moved and as they moved they effectively made holes in the asteroid belt?

David Minton: Exactly, so the planets formed probably in a tighter configuration, like Jupiter was a little further away from the sun, the other three gas giant planets, Saturn, Uranus and Neptune, when they were first born they were closer to the sun, so all four of these giant planets were in a much closer position to each other than they are now.

And at some point the giant planets began to migrate, and probably due to interactions with a more massive Kuiper belt, which is this icy belt of objects where Pluto lives. And that ancient Kuiper belt actually fuelled this migration and all four of the giant planets started to move from their original location, where they formed, to where find them today. And during that migration, the locations of these resonances in the asteroid belt which sculpts the Kirkwood Gaps, they had themselves also moved and as they moved they tossed asteroids out along the way, and so what we see today in the distribution of asteroids, is almost the footprint of the migration of these planets.

Chris Smith: And is this process, perish the thought, still happening today?

David Minton: No, what happened was that the Kuiper belt which was fuelling all this migration eventually ran out of mass, so the Kuiper belt we have today is like Pluto and Ares and some of these objects that themselves have been causing some controversy, they’re sort of the remnants of this ancient more massive disc and there’s almost nothing left out there, so there’s nothing to fuel the migration of the planets any more. And this migration probably happened over a very short period of time, it was probably very brief. It was probably very violent, you wouldn’t have wanted to have been on the earth when this was going on because all these asteroids when they were kicked out of the asteroid belt had to go somewhere, Earth would have been a major target for some of these objects. But that all ended fairly briefly and a very, very long time ago, probably about four billion years ago.

Chris Smith: David Minton from the University of Arizona, tracking what could be some of the largest footprints in the known universe. He’s published that work together with his colleague, Renu Malhotra, in this week’s edition of Nature.

[evan_au]

It is well known in mathematics that the general "three body problem" of gravitation produces unstable and chaotic behavior in the orbits.
- If one of the objects is massively heavier than the others (like the Sun is, in the Solar system), that slightly stabilizes the system, and allows a few stable orbits, as discovered by Lagrange.
- But the Solar System is a 9 (or more) body problem, and so mathematically, it is chaotic
- This resulted in many collisions in the early Solar System, and would explain planets changing places.
- Simulations on computers suggest that the Solar System should remain in its current configuration for hundreds of millions of years (barring outside influences).
- It is still possible (in the distant future) that planets could swap places or be completely ejected from the Solar System (or plunge into the Sun), at some point in the future

See: https://en.wikipedia.org/wiki/Chaos_theory