Why was the Kordylewski dust cloud observed more frequently at the L5 Lagrange point than at L4? Asymmetry of the particle capture at the triangular Lagrange points of the Earth-Moon system

Abstract

In 1961, the Polish astronomer, Kazimierz Kordylewski found dust clouds around the triangular Lagrange points L4 and L5 of the Earth-Moon system. After this discovery, several astronomers observed the Kordylewski dust clouds (KDCs) with photometry or ground-based imaging polarimetry, altogether 21 times. Remarkably, the L5 KDC has been detected three times (16) more than the L4 one (5). This may be due to varying sky and/or astronomical conditions during the KDC observations; for example, the Sun and Moon must be deep enough below the horizon, and the atmosphere must be as aerosol-free as possible. To reveal an additional possible physical reason for the asymmetric frequency of KDC observations, we performed computer simulations. We determined the particle capture at the L4 and L5 points in a 28-day period before the 21 published KDC observations. We found that the L5 point had by maximum 9% larger particle capture than L4, depending on the date of observation. We propose that this bias of the particle capture may be one of the reasons why the KDC has been observed more frequently around the L5 Lagrange point than around L4.