So, in this question, the user JollyJoker posted this image depicting the orbits of the asteroids in the asteroid field in the comments:


In this image, you can see that while the individual asteroids follow elliptical orbits, the asteroid belt as a whole is a giant triangle with the Jovian Trojans at two corners, and a third corner directly opposite Jupiter, and the whole triangle orbits in sync with Jupiter.

Is this image accurate? Is the Asteroid Belt actually a giant triangle, rather than the loose circle it is often depicted as? If so, why is this the case?

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    $\begingroup$ Scheirich has more visualizations of the inner solar system here. The main belt is shown in three shades of red. $\endgroup$ – Mike G Feb 12 '20 at 14:26
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    $\begingroup$ FYI that image host is considered "adult content" by some corporate blockers. $\endgroup$ – htmlcoderexe Feb 13 '20 at 9:52
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    $\begingroup$ You point out in the question that the individual red objects each have an elliptical orbit but the collection looks like a triangle that points away from Jupiter. A similar animation that shows more clearly that the individual objects have elliptical, not triangular orbits is here: sajri.astronomy.cz/asteroidgroups/hildaorb.gif $\endgroup$ – Eric Lippert Feb 13 '20 at 21:14

It's not. The image doesn't show the main asteroid belt. It shows the Jovian Trojans (in green) , and the Hilda Asteroids (in red).

The Hildas are a dynamical group of a few thousand known asteroids in elliptical orbits that are locked in a 3:2 orbital resonance with Jupiter, and reach aphelion coinciding with the regions near Sun-Jupiter Lagrange points L4, L3, and L5 in succession.

Animation showing Hildas with 3 indicated orbits, Petr Scheirich, 2005, 2018

"Animation showing Hildas with 3 indicated orbits" from "Asteroid (and Comet) Groups", Petr Scheirich, Retrieved 2020/02/14.

In accordance with Kepler's Second Law, objects in elliptical orbits move slower near aphelion than perihelion, and as a result, when you just look at the Hildas, they bunch up near the Lagrange points, and the pattern they appear to show at any one time resembles a triangle.

A more complete view of all the Asteroids inside of Jupiter looks like this.

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    $\begingroup$ youtube.com/watch?v=yt1qPCiOq-8 $\endgroup$ – uhoh Feb 12 '20 at 14:15
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    $\begingroup$ Not really coinciding with the Lagrange points, but approaching them – not because they are Lagrange points, but because those are the phases where an orbit with that period, with periapsis under Jupiter, must have its apoapsis. $\endgroup$ – Anton Sherwood Feb 13 '20 at 7:10
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    $\begingroup$ This video is both enlightning in showing where asteroids are, and also very mesmerizing to watch (it shows atseroids both orbiting and being discovered through the years) $\endgroup$ – Emil Bode Feb 13 '20 at 23:10
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    $\begingroup$ @Bilkokuya I've updated the answer with an image illustrating the elliptical orbits, and added some language about how they bunch up into the triangle. $\endgroup$ – notovny Feb 14 '20 at 12:39

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