The recent question Can dark matter accumulate at Lagrange points? mentions Kordylewski clouds and that article begins:

Kordylewski clouds are large concentrations of dust that exist at the L4 and L5 Lagrangian points of the Earth–Moon system.1,2,3 They were first reported by Polish astronomer Kazimierz Kordylewski in the 1960s, and confirmed to exist by the Royal Astronomical Society in October 2018.1,2,3

1AAAS's Eureka Alert October 26, 2018: Earth's dust cloud satellites confirmed

2Slíz-Balogh, Judit; Barta, András; Horváth, Gábor (11 November 2018). "Celestial mechanics and polarization optics of the Kordylewski dust cloud in the Earth–Moon Lagrange point L5 – I. Three-dimensional celestial mechanical modelling of dust cloud formation". Monthly Notices of the Royal Astronomical Society. 480 (4): 5550–5559. and https://arxiv.org/abs/1910.07466.

3Slíz-Balogh, Judit; Barta, András; Horváth, Gábor (1 January 2019). "Celestial mechanics and polarization optics of the Kordylewski dust cloud in the Earth–Moon Lagrange point L5 – Part II. Imaging polarimetric observation: new evidence for the existence of Kordylewski dust cloud". Monthly Notices of the Royal Astronomical Society. 482 (1): 762–770. and https://arxiv.org/abs/1910.07471.

Discussion in comments on the previous question's page relate to the notion that for a buildup of material, items, particles or whatnots to occur at Earth-Moon Lagrange points, these things should have some kind of non-conservative or dissipative interaction - in other words be able to lose energy so they can "fall in" to Lagrange point-associated orbits and stay there for a while.

As I understand it, since $1/r^2$ forces (e.g. gravitational, electrostatic) are conservative maybe something that dissipates energy (e.g. inelastic collisions converting some kinetic energy to thermal energy) might do the trick.

If this is all true (and I'm not saying it is) then I wonder:

Question: Are dust-dust collisions necessary to explain Kordylewski Clouds at Earth-Moon L4/5? Aren't the cross-sections too small to be significant considering the low number density of dust particles and short timescales involved?

Perturbations in the Earth-Moon Lagrange point system are strong - the Moon's orbit is significantly elliptical (non CR3BP) and the Sun's gravitational perturbation will also be significant. And of course for dust at 1 AU pressure from sunlight and electrostatic effects related to the solar wind may be important.

I'm having a hard time believing that it's dust-dust collisions that are the driving force behind the formation of the Kordylewski clouds, so I'm asking to be "straightened out" on my thinking here.

note: My current thinking is that collisions DO contribute to the accumulation of Trojan asteroids associated with the Sun-Jupiter L4/5 points. In this case all of the perturbing effects to dust with Earth-Moon L4/5 "accumulations" would not apply. Whether I'm right or wrong about that, the Trojans might be a good place to start before moving on to our local, dusty Kordylewski clouds.

  • 2
    $\begingroup$ You forget about interactions between photons and dust. a.k.a Poynting-Robertson drag. $\endgroup$
    – ProfRob
    Jun 22, 2023 at 14:49
  • $\begingroup$ @ProfRob omission was actually deliberate, I didn't forget about it (What is the origin of the dust near the sun?) If a particle is in heliocentric orbit photon pressure is radial just like the Sun's gravity so it's not really a perturber, but in the Earth-Moon rotating frame the Sun's gravity and photon pressure are now $1 \omega$ periodic perturbers (in the same direction) and for small enough dust could be comparable in magnitude. I guessed P-R drag would be weak in comparison, though still $1 \omega$ periodic. Was that incorrect? $\endgroup$
    – uhoh
    Jun 22, 2023 at 22:53
  • $\begingroup$ @uhoh Poynting-Robertson drag is absolutely relevant; it’s a form of drag, and thus a form of dissipation. It’s not “radial”, as you seem to think. $\endgroup$ Aug 14, 2023 at 22:44
  • $\begingroup$ @PeterErwin I said photon pressure is radial; that sentence doesn't refer to Poynting-Robertson (P-R) drag. The following sentences do refer to P-R and say that "I guessed P-R drag would be weak in comparison" to photon pressure, and that's why I did not include it. I said this to address ProfRob's "You forgot about", explaining that I didn't forget about it, I simply dismissed it as too weak to be important in the context of accumulation of dust at the triangular Lagrange points, then asked if thinking of it as too weak was wrong - to which no reply came. $\endgroup$
    – uhoh
    Aug 14, 2023 at 22:52
  • $\begingroup$ @PeterErwin do you think that the P-R effect is significant in the context of dust accumulation at L4/L5? If so, can you expand on that? $\endgroup$
    – uhoh
    Aug 14, 2023 at 22:54


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