High-resolution lunar gravity fields from the GRAIL Primary and Extended Missions

The resolution and accuracy of the lunar spherical harmonic gravity field have been dramatically improved as a result of the Gravity Recovery and Interior Laboratory (GRAIL) mission. From the Primary Mission, previous harmonic gravity fields resulted in an average n=420 surface resolution and a Bouguer spectrum to n=330. The GRAIL Extended Mission improves the resolution due to a lower average 23 km altitude orbit. As a result, new harmonic degree 900 gravity fields (GL0900C and GL0900D) show nearly a factor of 2 improvement with an average surface resolution n=870 and the Bouguer spectrum extended to n=550. Since the minimum spacecraft altitude varies spatially between 3km and 23km, the surface resolution is variable from near n=680 for the central farside to near n=900 for the polar regions. These gravity fields with 0.8 million parameters are by far the highest-degree fields of any planet ever estimated with a fully dynamic least squares technique using spacecraft tracking data. Key Points <list list-type="bulleted" id="grl51483-list-0001"> <list-item id="grl51483-li-0001">A degree 900 gravity field from the GRAIL Primary and Extended Mission <list-item id="grl51483-li-0002">The GRAIL Extended Mission doubles the resolution of the gravity field <list-item id="grl51483-li-0003">The Bouguer spectrum is well determined to near harmonic degree 550