I would like to have an asteroid belt "close" to a star. I want it to contain "large" asteroids. Is this plausible?

I believe the location of our real life asteroid belt is happenstance, due to Jupiter and various gravitational effects. So to an extent the location is fairly arbitrary.

However, I am looking for a certain total mass to be available. Forming an asteroid belt "far" from the star means there is a large playing field from which smaller particles can be scooped up. Close to the star there will be

  • a reduction in total available matter related to the square of the orbital distance,
  • distributed along a path whose length is related linearly to the orbital distance,
  • combining these effects tells me to expect, intuitively, that an asteroid belt 10 times closer would be 10 times less dense.

I also wonder whether the composition of the asteroids would be different. I would not be surprised to find that heavier atoms are thrown out less far by the supernova. Would this affect their formation?

What would it take to form a dense asteroid belt close to the sun, and how close could we reasonably expect it to happen, given suitable but plausible conditions?

(I would appreciate a hard science answer if possible.)

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    $\begingroup$ If you would like a hard science answer, why not use the hard science flag? It doesn't seem entirely unwarranted here. $\endgroup$ Mar 15 at 11:31
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    $\begingroup$ Available mass should not be a concern. You can always have some planet/moon beeing disturbed in its orbit, getting flung into the inner system and destroyed by the tidal forces of a hot jupiter. Those things can be very close to the star (about a star radius according to wikipedia). $\endgroup$
    – LazyLizard
    Mar 15 at 13:41
  • $\begingroup$ Ceres, the largest asteroid in the asteroid belt, is about 600 miles in diameter. Pluto is 1400 miles in diameter. Mercury is 3,000 miles in diameter. What do you consider a "'large' asteroid" to be? $\endgroup$
    – JBH
    Mar 16 at 1:00

2 Answers 2


There are a few misconceptions in this question. The first is that there's anything that we could call a typical stellar system, but we'll ignore that in favor of the popular idea that systems will form with the rocky planets in close and gas giants further out. What I'm describing isn't a hard rule, it's the set of rules that might apply if all stellar systems followed the same pattern as the Sun's planets.

Probably the most important misconception is that an asteroid belt could be dense. Anything resembling what you see in movies or television would accrete into a planet while the star was still young.

The proximity to the star won't be a determiner for density. Closer belts will have fewer asteroids because there won't be as much mass to accrete into bodies, but the overall density of rocks wouldn't be affected by this. The total mass of asteroids in your belt will be roughly 1/1000th the mass of the planet that would otherwise be in that orbital area.

An "orbital area" can be roughly defined via Bode's law. This states that each planet will be twice as far from the star as the previous one. When laying out your solar system, just replace one of the rocky planets with a bunch of asteroids.

There's a theory that the reason we don't have a fifth rocky planet between Mars and Jupiter is because Jupiter's gravity prevented that planet from forming. Having a "hot Jupiter" near the star might make your asteroid belt more realistic.


Its mostly gravity and the outcome of planets forming or gas-giants preventing the same, that affects the stability of asteroid belts. If you look at the solar-system, some out of the way- gas giant can prevent planetary formation via constant disturbance and destruction of any forming proto-planets.


Everything else depends on the asteroid. If it has volatiles (water, frozzen gas, basically a frozzen snowball) the energy of the sun + volatiles make for basically very slow and small thruster jets lifting a tumbling orbit.

A iron core/ rock asteroid will circle its sun till red-giant expansions slows it down and swallows it - or the intense light of flares + evaporating iron lifts it higher. If he is close enough to the sun, it might liquify him and over time blacksmith it into something entirely alien - like a red hot glowing iron sculpture made of noodles.

Finally all things move a tiny bit under light pressure. https://en.wikipedia.org/wiki/Radiation_pressure

Use this tool to calculate it. https://www.omnicalculator.com/physics/radiation-pressure - or just forget about it.

  • $\begingroup$ Light pressure decreases quadratically, just like gravity, thus I believe it does not cause deviation from the ordinary elliptical orbits. $\endgroup$
    – Gray Sheep
    Mar 15 at 16:59
  • $\begingroup$ @Gray sheep You are correct the effect of light and radiation pressure is minuscule. Its mostly gravity that affects asteroids.. $\endgroup$
    – Pica
    Mar 15 at 22:29
  • $\begingroup$ Yes and gravity + light pressure results only a little bit weaker gravity, because both decay in the same rate. $\endgroup$
    – Gray Sheep
    Mar 16 at 0:15
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    $\begingroup$ Point is asteroids start small and generally low density so thus when close to a sun (< 1AU )light pressure will have more affect then gravity compared to far away (>10 AU.) Not to mention light pressure applies force much differently then gravity. $\endgroup$ Mar 16 at 1:56
  • $\begingroup$ Mmh.. what if the iron asteroid - gets molten - and then the molten iron gets shaped into a thin, solar sail like structure of bubbles? $\endgroup$
    – Pica
    Mar 16 at 15:32

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