A different type of solar system. Help!

If you're going to write in that asteroid field, don't worry about the small stuff.

To be inhabitable by humans, a planets needs to have about 1g of gravity, i.e. same mass as earth, and about the temperature (well, and water, oxygen and other such details). Temperature is not determined by distance to the star alone, what matter is how much light per m² hits the planet. If the star is twice as bright as the sun, the planet would get the same amount of light at 1,4 AU. (inverse square law)
For that matter, you can vary the orbit of the earth quite a bit (at least by a third in either direction) and still have it inhabitable, at least partly, by humans.

I don't really know what you are after. But here are a few points. If the planet is in an asteroid belt, then a possible explanation might be that the belt was formed by the disintegration of a Trojan planet at the Lagrangian point on the opposite side of the star. Since no Trojan planets are known, it is a long shot and it would be an unstable system anyhow. It seems unlikely that the planet would attract the asteroids from other orbits (in the same way that the asteroid belt in our Solar System has not formed a cloud around Jupiter).

There is no reason for the planet to be 1 AU away from its sun. You could just alter the size of the star to make the planet habitable.

If the planet is huge, then gravity might be a problem. One way around that might be to make it spin very quickly on its axis.

telford said:

The other planets in the system have been pulverised (don't ask how) and have been attracted to the planet, causing it to be surrounded by a massive asteroid field. So here's the problem. If the planet is habitable to humans then it would have to be within one AU of the strongest graviational field (the primary) in the system.

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Is the habitable planet orbiting the star or the gravity sink? are we talking about a habitable moon of some gas giant?

Plus, putting a planet in the middle of an asteroid field would tend to mean a lot of asteroids hitting your planet, it seems to me. That tends to be rough on the living things on it...

carlaviii said:

Is the habitable planet orbiting the star or the gravity sink? are we talking about a habitable moon of some gas giant?

Plus, putting a planet in the middle of an asteroid field would tend to mean a lot of asteroids hitting your planet, it seems to me. That tends to be rough on the living things on it...

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The reason for having asteroids all around the planet escapes me. And I think Carlavii is correct in that if there were, the planet would be hit on a pretty regular basis.

However, if the planet previously had multiple moons, and those moons collided recently, then you might get asteroids around the entire planet. Eventually, you'll just have rings like Saturn though.

I don't think you can make the planet "really big" though. The bigger it is, the less dense it can be to maintain something close to 1g. The less dense it is, the more trouble it will have holding onto things in orbit and obviously, the less chance of having any kind of solid surface.

Unless you have a really, really good reaason for having the planet as you mentioned, huge and surrounded by asteroids, then you should drop those. A huge planet would either have a high mass that would lead to more gravity than humans could stand, or it would be of extremely low density, so that it couldn't have a solid surface.

An ordinary rocky planet of roughly the size of Earth would be appropriate. Something that recently created a lot of rocky debris might be O.K., but only if it serves the story.

telford said:

Thanks for that PeterL. Yes, as mentioned I have written myself into a corner all right. As I see the story now it is vital that this environment work. I guess that I will have to take a bit more time to think this throught. I appreciate you taking the time.

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1.6g is not very large, so you don't have that much of a problem there, except that it would be very unlikely to capture all that many asteroids. You might consider giving the planet multiple moons. A dozen or two moons would knock some chunks off each other, but they would establish stable orbits fairly quickly. The debris would be swept to other orbits.

The universe is a really really big place. I mean REALLY big. Seems possible that somewhere or other a planet might end up with what amounts to a huge number of big rocks in stable orbits. Unlikely (very!), but it doesn't seem impossible.

DavidZahir said:

The universe is a really really big place. I mean REALLY big. Seems possible that somewhere or other a planet might end up with what amounts to a huge number of big rocks in stable orbits. Unlikely (very!), but it doesn't seem impossible.

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It's impossible because huge amounts of rock cannot have a stable orbit. They will condense down to a single body per orbit. Even different orbits that are too close together (so close that minor alterations cause collisions) don't work.
It's the same reason you can't have asteroid fields like you see them on StarWars or nebulae like the ones on Star Trek. Gravity sucks.

telford said:

Peter, Lhun & David,
Thanks guys for the input. Yes, by the physics we currently understand, this is an impossible situation. But in the first book I altered the laws of physics and got away with it (I think). This is, after all, a science fiction book, so perhaps a bit of latitude could be expected if I apply the bs with a very delicate brush. Thanks again guys.

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Well, maybe it works. But you need some serious physics alterations to make those asteroids work. There'd need to something that keeps those asteroids from bumping into each other, but at the same time does not prevent planets from forming. (which happens by asteroids bumping into each other)

Maybe I'm coming at this with a different sense of just how many rocks we're talking about here?

Lhun said:

It's impossible because huge amounts of rock cannot have a stable orbit. They will condense down to a single body per orbit. Even different orbits that are too close together (so close that minor alterations cause collisions) don't work.
It's the same reason you can't have asteroid fields like you see them on StarWars or nebulae like the ones on Star Trek. Gravity sucks.

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Except that there is the Asteroid Belt in our own Solar System. I'm not sure what the latest theories are on its formation, but it has been proposed that it was caused by the destruction of a planet (Phaeton). There are also fields of asteroids at the Lagrangian points in Jupiter's orbit (these are stable points on the same orbit). It is possible that a planet corresponding to a Lagrangian point on the same orbit as the planet in the story created the asteroid field. This type of planet is called a Trojan planet; although none are known there are Trojan moons (orbiting Saturn).

Lhun said:

It's impossible because huge amounts of rock cannot have a stable orbit. They will condense down to a single body per orbit.

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Sure they will. But over how long?

After a few million years? Ten million?

Couldn't it just be a fairly 'young' asteroid field - with scientists guessing that it was only formed in the last 100,000 years or so - but really not sure?

Mac

Kenn said:

Except that there is the Asteroid Belt in our own Solar System. I'm not sure what the latest theories are on its formation, but it has been proposed that it was caused by the destruction of a planet (Phaeton). There are also fields of asteroids at the Lagrangian points in Jupiter's orbit (these are stable points on the same orbit). It is possible that a planet corresponding to a Lagrangian point on the same orbit as the planet in the story created the asteroid field. This type of planet is called a Trojan planet; although none are known there are Trojan moons (orbiting Saturn).

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The asteroid belt in the solar system contains considerably less rock than, say, the vacuum inside a light-bulb. It's total mass is a small fraction of the moon's, and even that is concentrated mostly in few big asteroids.

Mac H. said:

Sure they will. But over how long?

After a few million years? Ten million?

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Well, that's a question of how many rocks there are, and how they are spread out.

Couldn't it just be a fairly 'young' asteroid field - with scientists guessing that it was only formed in the last 100,000 years or so - but really not sure?

Mac

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That leaves the question where all the rock came from. And even if it's just around a planet, not a whole belt, that can be a whole lot of rock. Smashing a planet or even moon into separately orbiting fragments takes an insane amount of energy, so much that it's kind of impossible that it could happen in the orbit of another planet and leave that one undisturbed.

telford said:

Lhun & David,
I'm open to ideas but I see a massive field formed from dozens of destroyed planets (perhaps during the ancient war 5000 years ago). A thought that jumped into my head recently was this: If the asteroids and the planet contained an element that attracted one another that would solve the first problem. Then perhaps like two magnets pushing against one another this would create a stable situation. Attraction at a distance, repulsion up close, with both scources constantly working against one another to maintain the stability. If you like you may call this element bullshitium. (just kidding guys)
Any thoughts?

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As Lhun mentioned, if we're talking about recently destroyed planets (and 5,000 years is recent, as these things go) then you're throwing orbital changes into the mix too. The web of interplays between the star's gravity and all of the planets tugging on each other has been broken up. Your planet's orbit could still be adjusting to the change.

Which could make for interesting situations, like a frozen planet sliding a little closer to its star and starting to thaw out...

I could be talked into the planet picking up a debris ring like Saturn's from all the mess. But yeah, if you want to put some kind of protective field around your planet to protect it from bombardment, that would be bullshitium.

Lhun said:

The asteroid belt in the solar system contains considerably less rock than, say, the vacuum inside a light-bulb. It's total mass is a small fraction of the moon's, and even that is concentrated mostly in few big asteroids...

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That is an odd comparison, since there is no rock floating around inside a light bulb.

The mass of the asteroid belt is still pretty much unknown (despite what Wikipedia might say!). Of course it has become depleted with time, thanks to Jupiter's influence, but it hasn't always been like that. You only have to look at the surface of the moon to see how much more stuff was kicking around in the past. Don't forget there are a lot of meteor strikes on earth every year also.

I imagine the asteroid fields in sci-fi films are explained as being the remnants of planets. I am not quite sure why a planet would disintegrate, or even if it could, but you can't make sweeping statements about the energy it would require. For example, you might imagine gravitational resonance could shatter a crystaline core or crust.

Kenn said:

That is an odd comparison, since there is no rock floating around inside a light bulb.

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And to a similar degree of accuracy, there are no rocks floating around in the asteroid belt. It's emptier than the best man-made vacuum.

The mass of the asteroid belt is still pretty much unknown (despite what Wikipedia might say!).

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No it's not. We haven't found every pebble floating around there, but that's it: they're just pebbles. It doesn't really matter if we don't know the mass of the asteroid belt to the tenth decimal or only the ninth.

Of course it has become depleted with time, thanks to Jupiter's influence, but it hasn't always been like that. You only have to look at the surface of the moon to see how much more stuff was kicking around in the past. Don't forget there are a lot of meteor strikes on earth every year also.

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All of that is small stuff. You could scatter the whole moon across the asteroid belt and it'd still empty. Not even dense enough to see two asteroids at once.

I imagine the asteroid fields in sci-fi films are explained as being the remnants of planets. I am not quite sure why a planet would disintegrate, or even if it could, but you can't make sweeping statements about the energy it would require. For example, you might imagine gravitational resonance could shatter a crystaline core or crust.

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Again, gravity prevents all this. Planets can't shatter because they're not really solid anyway. The problem is that what you're used to on earth, doesn't work like that when scaled up a couple of billion times in space. A rock holds together because of intermolecular bonds, and if you break rock into pieces, they don't stick together. You can break a rock and scatter it across the ground.
But it doesn't work that way in space. Planets are for all intents and purposes just liquids, the hardness of the materials is completely irrelevant because of the forces involved. A planet isn't spherical because it's a piece of rock that just happens to be spherical, but because the pull of gravity is so strong that it simply forms a sphere. I you pick a planet made of solid rock, and crush it to dust, you still end up with a spherical pile of dust floating around. To completely scatter a planet you need to accelerate all its matter to escape velocity. Which can easily exceed the energy required to vaporize the matter. In which case you'd still end up with a spherical blob of vaporized rock.

telford said:

A thought that jumped into my head recently was this: If the asteroids and the planet contained an element that attracted one another that would solve the first problem.

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Gravity does that anyway.

Then perhaps like two magnets pushing against one another this would create a stable situation. Attraction at a distance, repulsion up close, with both scources constantly working against one another to maintain the stability. If you like you may call this element bullshitium. (just kidding guys)
Any thoughts?

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The problem with scenarios like these is that they're rarely self-correcting. If the balance tips just a little, the whole system comes (metaphorically) crashing down.
But sure, magically repellent bolognium that keeps the rocks from falling on the planet and from forming a moon works. Though you should find some kind of explanation why the bolognium in the rocks keeps them from forming a single body, but the bolognium in the planet doesn't cause it to fly apart.