P41C-2077
High-resolution gravity models for Mercury from MESSENGER tracking data

Thursday, 17 December 2015
Poster Hall (Moscone South)
Sander J Goossens1, Erwan Mazarico2, Antonio Genova3, Frank G Lemoine4, Gregory A Neumann5, Maria T Zuber6, David E Smith3 and Sean C Solomon7, (1)University of Maryland Baltimore County, Baltimore, MD, United States, (2)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (3)Massachusetts Institute of Technology, Cambridge, MA, United States, (4)NASA Goddard SFC, Greenbelt, MD, United States, (5)NASA, Baltimore, MD, United States, (6)Massachusetts Inst Tech, Cambridge, MA, United States, (7)Columbia University of New York, Palisades, NY, United States
Abstract:
On 30 April 2015 the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft completed its mission of slightly more than 4 years of operations in orbit around the planet Mercury. To meet mission thermal constraints, MESSENGER’s orbit around Mercury was eccentric, with a periapsis located at high northern latitudes. During its primary mission, the periapsis altitude was maintained between 200 and 500 km. For more than two years thereafter, the periapsis altitude was left to evolve naturally, reaching a maximum of 450 km in March 2013, after which it started to decrease. In MESSENGER’s second extended mission, altitudes as low as 15–25 km above the surface of Mercury were achieved.

Radio tracking data acquired by the Deep Space Network (DSN) at the X-band frequency have been used to determine models of the gravity field of Mercury. The resolution of these global models, expressed in spherical harmonics, increased as data at lower altitudes became available. However, because of MESSENGER’s eccentric orbit, the data cover only the northern hemisphere, and coverage is less dense toward the equator. Local solutions, which use basis functions that do not have global support, are especially suitable to handle such uneven data coverage.

Here, we present gravity field solutions based on gravity anomalies arranged on a grid with a resolution of 1 degree by 1 degree. We use line-of-sight derivatives of Doppler data, which are obtained by numerical differentiation of the time series of DSN tracking data. Our local solution covers the northern hemisphere from 10° N to 88° N. Our solution shows increased correlations with topography in areas with low-altitude data coverage. We also compare our local solution to global models of similar resolution.

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