Seasonal and static gravity field of Mars from MGS, Mars Odyssey and MRO radio science

Abstract

We present a spherical harmonic solution of the static gravity field of Mars to degree and order 120, GMM-3, that has been calculated using the Deep Space Network tracking data of the NASA Mars missions, Mars Global Surveyor (MGS), Mars Odyssey (ODY), and the Mars Reconnaissance Orbiter (MRO). We have also jointly determined spherical harmonic solutions for the static and time-variable gravity field of Mars, and the Mars k2 Love numbers, exclusive of the gravity contribution of the atmosphere. Consequently, the retrieved time-varying gravity coefficients and the Love number k2 solely yield seasonal variations in the mass of the polar caps and the solid tides of Mars, respectively. We obtain a Mars Love number k2 of 0.1697 ± 0.0027 (3-σ). The inclusion of MRO tracking data results in improved seasonal gravity field coefficients C30 and, for the first time, C50. Refinements of the atmospheric model in our orbit determination program have allowed us to monitor the odd zonal harmonic C30 for ∼1.5 solar cycles (16 years). This gravity model shows improved correlations with MOLA topography up to 15% larger at higher harmonics (l = 60–80) than previous solutions.