New observations of Phobos, Deimos, and their shadows with the HRSC/SRC on Mars Express

Abstract

In the past year, many new observations of Phobos and Deimos have been carried out by the HRSC (High Resolution Stereo Camera) and the SRC (Super Resolution Channel) on the Mars Express spacecraft. A total of 3 Phobos flyby maneuvers were executed within one November week (2005) alone. In addition, the Phobos shadow was captured twice, in orbits 2239 and 2345, as it moved across the surface. As we reported previously, the earlier observations were used to determine the astrometric positions of the two satellites with accuracies of 0.5 - 5 km (Phobos) and 1.0 km (Deimos). These positional data differed substantially from the various available predictions, a fact which motivated the beginning of renewed Phobos and Deimos orbit modeling efforts. On the observational side, efforts were made to refine the astrometric measurements: for the HRSC observations carried out in the second half of this year, the planning software was upgraded, to maximize the number of background stars in the images for improved camera pointing control. The new data can be used to confirm and further improve the accuracy of the satellite orbit models. These models bear important implications on tidal dissipation and internal structure of Mars.