Observations of Phobos and its shadow: Implications for the Phobos orbit

Abstract

The orbit of Phobos deep in the gravity field of Mars is strongly affected by various parameters of the Mars interior. The orbit of the small satellite is therefore complex and undergoing a particulate tidal evolution. Our early analysis of im-ages from High Resolution Stereo Camera / Super Resolution Channel (HRSC/SRC) on Mars Express (MEX) [4] have shown stark discrepancies between orbit models and observations of up to 12 km, a fact which renewed the interest in more detailed astro-metric analysis of Phobos data to constrain the orbit models. Since these early studies, we have made a number of new astrometric measurements using new image data and upgraded measurement techniques. The Mars Express spacecraft has continued its Phobos flyby maneuvers and has obtained many more SRC images of the satellite. In addition, the shadow of Phobos was captured on several occasions by the HRSC and the Mars Orbiting Camera (MOC) on the Mars Global Surveyor, which all had not been analyzed yet. These shadow observations provide further constraints on the orbit of Phobos not affected by uncertainties in the spacecraft orbit and camera pointing. In the presentation, we will report on first preliminary results of our ongoing study titled ,Geodesy and Cartography of Phobos", funded by DFG.