Possibility of multiple planets sharing the same orbit?

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Discussion Overview

The discussion revolves around the possibility of multiple planets or planetoids sharing the same orbit, particularly focusing on the stability of objects at Lagrange points in a star system. Participants explore theoretical implications, definitions of celestial bodies, and the gravitational dynamics involved.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that while Jupiter shares its orbit with asteroid groups (Jupiter trojans), the formation of planets at Lagrange points may be hindered by gravitational interference, suggesting that these points may only support asteroid fields.
  • Others argue that the definition of a planet requires it to have cleared its orbit of comparable-sized objects, implying that any object sharing an orbit with Jupiter cannot be classified as a planet.
  • A few participants mention that dwarf planets could exist at these points, referencing specific examples from the Jupiter Trojans.
  • It is noted that only Lagrange points L4 and L5 can offer stable orbits, but only for objects significantly smaller than the main planet.
  • Some participants express uncertainty about the stability of multiple objects at L4 and L5, suggesting that gravitational dependencies might limit the number of stable bodies that can coexist.
  • There is a discussion about the need for proper analysis when considering the mass of Trojans and their potential effects on stability at L4/L5, with references to theoretical models like the Klemperer rosette.

Areas of Agreement / Disagreement

Participants generally agree on the definitions of planets and the stability conditions at Lagrange points, but multiple competing views remain regarding the feasibility of having multiple large bodies sharing an orbit and the implications of mass ratios on stability.

Contextual Notes

Limitations include the dependence on definitions of celestial bodies, unresolved mathematical steps regarding stability analysis, and the need for further exploration of configurations that could allow for multiple massive objects in co-orbiting scenarios.

Aldarion
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TL;DR
Possibility of multiple planets sharing the same orbit?
So I remembered that Jupiter shares his orbit with two asteroid groups (Jupiter trojans) at Lagrange points in its orbit. So I want to ask, is it at all possible for planets or planetoids to be formed at Lagrange points in a star system, or will gravitational interference always ensure that it is either an asteroid field or nothing?
 
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I think that technically you can't have a planet, because the definition of a planet requires it to have cleared its orbit of other stuff anywhere near comparable size (excluding moons). So any object sharing an orbit with Jupiter is not a planet by definition.

Dwarf planets are possible. Have a look at the wiki article on co-orbital objects.
 
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Ibix said:
I think that technically you can't have a planet, because the definition of a planet requires it to have cleared its orbit of other stuff anywhere near comparable size (excluding moons). So any object sharing an orbit with Jupiter is not a planet by definition.

Dwarf planets are possible. Have a look at the wiki article on co-orbital objects.
By planet, I meant an orbital body large enough to be more or less perfectly spherical. So basically like Janus and Epimetheus, but orbiting a star.
 
Those would be dwarf planets. The wiki article I linked lists a few objects that fit the bill - at least one of the Jupiter Trojans is larger than the two satellites you cited.
 
According to this, Only Lagrange points L4 and L5 can offer stable orbits, and then only for objects 1/25th the mass of the main planet or less.

Note: This is the first time I have noticed a DuckAssist AI(?) answer. It seemed very helpful.
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FactChecker said:
According to this, Only Lagrange points L4 and L5 can offer stable orbits, and then only for objects 1/25th the mass of the main planet or less.
So, Jupiter could keep two Uranus' in his harem - one at each L.
 
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DaveC426913 said:
So, Jupiter could keep two Uranus' in his harem - one at each L.
I am ignorant on this subject, but there might be a dependency between objects at L4 and L5 which disturbs their orbits. It might only work for one at a time. I'm afraid that I have already gotten out of my lane and should leave this for others.
 
FactChecker said:
I am ignorant on this subject, but there might be a dependency between objects at L4 and L5 which disturbs their orbits. It might only work for one at a time. I'm afraid that I have already gotten out of my lane and should leave this for others.
I doubt it. They're 120 degrees - a billion miles - apart. That's bigger than the entire inner solar system's diameter.

Saturn and Mars are each less than half that distance.
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Sorry. I got my numbers wrong. Google has helpfully corrected me.

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  • #12
Their answer is only out by one tenth of a crore.
That is 6 orders of magnitude to a human;
or 20 orders of magnitude to a computer.
 
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When talking about mass ratios for L4/L5 stability note that the masses involved are the primary and the secondary, not the third "test" particle. So for the Sun/Jupiter system L4 and L5 is considered stable for a test particle. If the third object has mass comparable with the secondary a different (likely numerical) analysis is probably needed to establish stability. I seem to recall there are several "constructed" configurations of multiple massive objects around a primary that can be shown to have periodic trajectories, e.g. like the Klemperer rosette, but if one want to only considered "natural occurring" co-orbiting configurations I would would expect most of those configurations to be very unlikely as any configuration also has to fit into models of solar system formation.
 
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  • #14
I would suspect that when the mass of the Trojan is such that its potential is anywhere near the depth of the L4/L5 potential well then you need to do some proper analysis. That's just a guess, though - Spivak's book (referenced in @FactChecker's link in #5) might shed more light.
 
  • #15
Thanks!
 
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