Gravity field of Mars: A 75th degree and order model

Radiometric tracking data collected by NASA's Deep Space Network (DSN) for Mariner 9, Viking 1 and 2 orbiters, and Mars Global Surveyor (MGS) have bee n analyzed to determine the gravity field of Mars. The gravity solution (MG S75D) is a complete spherical harmonics model to degree and order 75. Also parts of the solution are the gravitational constants of Mars, Phobos, and Deimos. The significant improvement in the MGS75D Mars gravity model is mai nly a consequence of globally distributed data set collected from the MGS m apping orbits, the use of optimal weighting and constrained least squares s olution techniques, and improved force and measurement models in the orbit determination process. The gravity anomaly map reveals significantly more d etail and larger amplitudes than any previous Mars gravity map over the maj or impact and volcanic areas on Mars. Olympus Mons remains the largest know n gravity anomaly in our solar system and Isidis Planitia, the highest-ampl itude mascon. There are mascons in the Hellas, Argyre, and Utopia basins. V alles Marineris has distinctive negative anomalies, and all volcanic featur es are positive. Gravity anomalies over several craters have also been reso lved. The overall correlation of the MGS75D gravity anomaly map with topogr aphy derived from the Mars Orbiter Laser Altimeter (MOLA) is very high, whi le the polar regions display relatively poor correlation.