In recent years satellite observations of the region of the Earth-Moon libration points L4 and L5 became available, which showed different results. Roach (1975) has measured perturbations of the Zodiacal Light intensity near the libration points L4 and L5 with a photometer on board the OSO-6 satellite. He interpreted the results as counterglow of a cloud of particles, having an angular diameter of 6 degrees and an average brightness of 20 S10v, whereas observations by Burnett et al. (1974) set an upper limit of 10 S10 blue. Earth bound observations made by Bruman (1969) with the 48-inch Palomar Schmidt telescope gave no indication for discrete objects nor for clouds.
AbstractThe Sun-Earth libration points, L1 and L2, are located 1.5 million kilometers from the Earth towards and away from the Sun. Halo orbits about these points have significant advantages for space observatories in terms of viewing geometry, thermal and radiation environment, and delta-V expediture.
1.3.5 On the Visibility of the Libration Clouds