Talk:Co-orbital configuration

illusion or montage?

I'm puzzled by this picture caption:

Epimetheus and Janus seen on 20 March 2006, two months after swapping orbits. The close proximity between the two moons is an illusion; they are actually being seen on opposite sides of their common orbit.

If they're on opposite sides of Saturn, they can't be seen like this! If "opposite sides" merely means above and below their average height, the sentence is non-sequitur; that is to be expected and does not preclude proximity. Does it really mean the picture is a composite of separate shots? —Tamfang (talk) 20:49, 14 June 2009 (UTC)

Looking at the picture's description on its summary page, it says it is an illusion because Janus is actually 25,000 miles farther away than Epimetheus. The caption should probably just say that instead. I'll change it. Slim (talk) 19:09, 2 November 2009 (UTC)

co-orbital planets

Kepler, apparently, may have found co-orbital planets. They are still in "candidate" phase, waiting for confirmation.

Do candidate planets count? If so, should this become the "co-orbital astronomical object" page? ("co-orbit"?) More curious than anything else.

68.183.80.244 (talk) 07:12, 3 February 2011 (UTC)

References

Lagrange Points

The Lagrange Points L4 & L5 are not exactly in the orbit of the secondary, which means that the use of 60 degrees in the article is inexact. The triangle (L4/L5, primary, secondary) is exactly equiangular. 94.30.84.71 (talk) 09:41, 16 June 2012 (UTC)

Retrograde and prograde

As currently written, the article says “(or 1:-1 if orbiting in opposite directions)”. My non-expert reading of some of the easier literature suggests that the mechanisms just don’t happen if the things are orbiting in opposite directions. If the dynamics still work, more needs to be said. If they don’t, as I suspect, then this phrase should be deleted. JDAWiseman (talk) 00:23, 16 November 2013 (UTC)

I've added a ref for this. Astredita (talk) 02:23, 16 November 2013 (UTC)

Going by the cited paper, this is an incredibly rare thing, and looks like it's a temporary, and only predicted rather than observed situation that is expected to happen sometime in the next 20,000 years between Saturn and a single small asteroid. Presumably it will either pass quite close to the planet and be immediately perturbed out of its orbit (having held it for maybe a few years at most), or crash straight into it or one of its moons, unless it has a relatively high inclination and/or eccentricity that means, with the help of the 1:-1 resonance, it's always at a different height above/below the ecliptic or at a somewhat different distance from the sun when the planet and its moons sweep past. All the other (still fairly rare) stated retrograde resonances are non-unity fractions, suggesting a wholly separate orbital path around the sun and potential interactions only with other (prograde) centaur asteroids, which are much, much smaller and (literally) less attractive targets, meaning a collision would be exponentially less likely.

I have a feeling all that means it's maybe not worth including the "-1" possibility in the lede, or at least it warrants an explanatory footnote along those lines to clarify for the moderately informed and understandably confused that a) it doesn't happen hardly ever in nature - like once, for a short time, every few millennia, and the situation is most likely terminated within the space of half a local year by the smaller partner being gravitationally hurled into an entirely different orbit when it meets the larger (rather than necessarily colliding with it); and b) space is big, like REALLY BIG, and resonances are rarely absolutely exact or devoid of precession, so something can be in nominally the same orbit as a major planet - either prograde or retrograde - but still not on anything like the exact same track as it, and therefore still unlikely to collide, especially if their synchronised orbital mechanics mean there's always going to be some separation between them at their twice-per-orbit path crossings... 51.7.16.171 (talk) 12:58, 5 August 2019 (UTC)

An asteroid 514107 Kaʻepaokaʻawela was discovered in 2015 that is in a retrograde 1:1 resonant orbit with Jupiter that has been stable for a million years see https://arxiv.org/abs/1804.10893 That paper however does not use the notation 1:-1 Fdfexoex (talk) 06:12, 31 August 2019 (UTC)

Update "Trojan minor planets" section

How about update info from more recent discoveries about Uranus trojans, Neptune trojans, and some temporary Venus trojans?--Bobbylon (talk) 12:10, 2 May 2017 (UTC)

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1:-1 orbit?

This stat in the first paragraph confuses me, how can two bodies share an orbit yet be moving in opposite directions? Wouldn't they collide? I don't see how a 1:-1 mean motion resonance is possible with physical objects that could hit each other. Caelus5 ^{Chat∞Contribs} 14:09, 7 March 2018 (UTC)

Trojan/Greek nomenclature?

I've seen it in many places here that asteroids in the leading L4 coorbital position relative to Jupiter are called "Greeks" rather than "Trojans", and only those in the trailing L5 position are uniformly called "Trojan" in all sources. Is that a thing unique to Jupiter and the naming conventions adopted for its particular trojan asteroids, or would that also extend to the L4 vs L5 groups around other planets / moons? If not, why not, given that it seems a fairly neat and easy way of distinguishing the two largely non-interacting groups (horseshoe orbits notwithstanding)? 51.7.16.171 (talk) 12:49, 5 August 2019 (UTC)

This naming scheme is unique to the Jovian Trojans. They are named after heroes of Trojan War, Greeks and Trojans, respectively. The Trojans of other planets are not named after Trojan War heroes. Ruslik_Zero 16:52, 5 August 2019 (UTC)

180° from larger body = L3?

Current text: ... L4 and L5, 60° ahead of and behind the larger body respectively. Another class is the horseshoe orbit, in which objects librate around 180° from the larger body

Is "180° from the larger body" the L3 point? If so shouldn't L3 be mentioned, as L4 and L5 are? If not, perhaps this should noted. Jdthood (talk) 07:53, 8 October 2019 (UTC)