Analogues of interplanetary dust particles to interpret the zodiacal light polarization

Abstract

ContextSome local properties of the dust particles that build the interplanetary dust cloud may be deduced from the light they scatter (with emphasis on their linear polarization). The ratio of organics (absorbing particles) to silicates (more transparent particles) was suggested through numerical simulations to reproduce the shape of the polarimetric phase curve and the decrease in polarization with decreasing solar distance. AimsReproducing these properties, through measurements on real dust particles lifted in microgravity conditions, in the PROGRA2 light scattering experiment. Using dust analogues with parameters similar to those derived from numerical simulations. MethodsAnalogue particles, previously tested for the two main sources of dust in the inner interplanetary cloud (comets and asteroids) were used in the experiment. The ratio between fluffy aggregates and compact particles was kept constant. Five samples were studied, corresponding to mixtures with the organics / silicates ratio as defined in the numerical simulation. ResultsWe show that we can reproduce by experimental simulations the polarimetric properties of particles present in the inner interplanetary dust cloud, i.e. their polarimetric phase curve in the symmetry plane at 1.5 au from the Sun and variations of polarization at a 90° phase angle as a function of the solar distance between 0.5 au and 1.5 au. The effect of the different parameters suggests a size distribution of the particles following a power law with coefficients of (−3 ± 0.5) for a size-range of 10–100 μm and (−4.4 ± 0.6) for a size range of 100–200 μm, with a steep cutoff at about 10 μm, a constant ratio of (35 ± 10) % in mass of fluffy aggregates versus compact particles and a decreasing ratio of organics with decreasing solar distance. Such results are discussed in the context of recent evidence on cometary dust particles from the Rosetta mission to a Jupiter family comet.