New Solutions for the Mars Static and Temporal Gravity Field using the Mars Reconnaissance Orbiter

The Mars Reconnaissance Orbiter entered low-altitude orbit about Mars in August 2006, and has since completed one Mars year in the mapping orbit. The orbit, with a periapsis of 255 km and and apoapsis at 320 km, allows for a higher resolution of the Mars gravity field, compared to earlier models based on data from combinations of Mars Global Surveyor and Mars Odyssey, which had periapsis altitudes of 370 to 390 km. In this paper, we present the new solutions developed at NASA GSFC up to 100x100 in spherical harmonics using X band tracking data from NASA's Deep Space Network, combining data from all three missions. The new solutions extend the resolution of the static field -to about l=85 (compared with l=65 to 72 based on MGS or MGS+Odyssey alone), and the correlation with topography is also improved compared to previous solutions, with values of 0.6 at l=80. We note that the resolution is not spatially uniform due to the eccentricity of the MRO orbit, and the resolution of the static field is slightly greater over the Southern Hemisphere, than the Northern Hemisphere. Using data from Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter, we are also able to construct a time history of the temporal variations in the low degree Mars gravity field for over five Mars - from March 1998 to the present, reflecting mass transport in the Mars system.