Light scattering by solar system dust : image reconstruction of the lunar sunrise sketches drawn by the Apollo 17 crew

Abstract

In 1972, astronauts on board Apollo 17 saw a lunar sunrise while they were in orbit around the Moon. They made drawings of the distribution of light above the lunar horizon, which has been called "the lunar sunrise sketches". The sunrise sketches by the Apollo 17 crew have been interpreted to contain light scattered by interplanetary dust as well as light scattered by dust in the close vicinity of Moon. In this thesis the light scattering by interplanetary dust and by a micrometeoroid impact-generated lunar ejecta cloud at the time of Apollo 17 sunrise sketches is modeled and an image is reconstructed for the same observation geometry that can be compared to the sunrise sketches. To determine the contribution of light scattered by different dust populations, we need to know their dust number densities, the respective light scattering properties of the dust as well as the precise geometry of the observations.

A model for the interplanetary dust distribution is constructed using the results of COBE DIRBE team. Scattering properties of interplanetary dust are described with a combination of empirical scattering function for intermediate and high scattering angles and with a Frauenhofer diffraction for small scattering angles. For the lunar ejecta cloud we use a model derived from in situ measurements of the lunar dust cloud by LADEE probe. Scattering properties of the dust grains in the lunar ejecta cloud are calculated using Lorenz-Mie theory. The location of the Apollo 17 spacecraft is determined based on the orbital information given in the flight report. Finally images of the lunar orbital sunrise are reconstructed using the known sight-line geometries and dust configurations together with their scattering properties. In the reconstructed images zodiacal light appears dominant and similar to that in the sunrise sketches. Light scattered by the lunar ejecta cloud is instead weak and not visible in front of the zodiacal light.