Revised Ephemerides of the Martian Satellites, Phobos and Deimos

Abstract

We report on the new ephemerides (MAR099) for the satellites of Mars derived from a large set of ground-based and spacecraft astrometric measurements. Our integrated orbit fit yielded latest estimates for the Martian tidal parameter τ = k 2/Q = 1.816 ± 0.084 × 10−3 and half the tidal acceleration of Phobos of s = 1 2 n ̇ = 1.258 ± 0.058 × 1 0 − 3 deg yr−2. We used the spacecraft-measured physical libration amplitude of Phobos, A = 1.14 ± 0.03 deg, to fit J 2 and C 22 and found that the result is consistent with the value derived from its shape and the uniform density assumption. The data show no sensitivity for the physical libration of Deimos. We report on the statistics of the observation residuals, the satellites’ orbital elements, and projected uncertainties of the satellites’ positions in the next few decades.