Phobos control point network, rotation, and shape

A new independent control point network for Phobos was computed from image data obtained by the SRC (Super Resolution Channel) on board the European Mars Express Mission. The network solution includes 3D coordinates of 665 surface control points and was used to observe the forced libration amplitude of Phobos. Based on the network control points a spherical harmonic function model to degree and order 17 was derived, from which volume, bulk density and moments of inertia were computed. The modeled forced libration amplitude agrees to our observation within the error bands, indicating a homogeneous mass distribution for Phobos. To bring both values into exact agreement with the observations, different mass distribution models were applied. It appears that the amplitude is relatively insensitive to a simple two-layer density model.