Updated Mars Orientation and Gravity Field and Indication of Decadal Changes in Rotation Rate

The Mars orientation is determined from a combination of spacecraft orbiter tracking data from Mars Reconnaissance Orbiter (MRO), Mars Odyssey, and Mars Global Surveyor (MGS), and Mars lander tracking data that includes Viking Lander 1 and 2, Mars Pathfinder, and InSight. This new orientation model includes an additional 6 yr of orbiter data as well as InSight tracking data versus previous orbiter-based solutions and is consistent with InSight orientation results. In addition, the Mars model includes a higher-precision Mars nutation model to 1 mas accuracy and corrected relativistic terms for seasonal rotation rate. Although the landers are more sensitive to the rotation rate (∼4x), the orbiters provide evidence of long-term changes in the rotation rate of Mars as well as a more accurate Mars spin pole location in inertial space (2–3x). The long-term spin solution is modeled as a 245.7 ± 7.7 mas 25.8 ± 0.5 yr oscillation in the location of the prime meridian. The Mars orientation is a joint solution with a new improved spherical harmonic degree n = 120 gravity field MRO120G and with 1 m accuracy in pole location (1950–2050) and 1–10 m accuracy in relative prime meridian location.