Mercury's gravity, tides, and spin from MESSENGER radio science data. Issue 9 (5th September 2016)

• Record Type: Journal Article
• Authors: Verma, Ashok Kumar; Margot, Jean‐Luc
• Is Part Of: Journal of geophysical research. Volume 121:Issue 9(2016:Sep.)
• Page Start: 1627
• Page End: 1640
• Publication Date: 2016-09-05
• Subjects: Mercury -- MESSENGER -- Gravity -- Love number -- Spin axis; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1002/2016JE005037
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: We analyze radio tracking data obtained during 1311 orbits of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft in the period March 2011 to April 2014. A least squares minimization of the residuals between observed and computed values of two‐way range and Doppler allows us to solve for a model describing Mercury's gravity, tidal response, and spin state. We use a spherical harmonic representation of the gravity field to degree and order 40 and report error bars corresponding to 10 times the formal uncertainties of the fit. Our estimate of the product of Mercury's mass and the gravitational constant, G M = (22031.87404 ± 9×10 −4 ) km 3 s −2, is in excellent agreement with published results. Our solution for the geophysically important second‐degree coefficients ( C ̄ 2, 0 = − 2 . 25100 × 1 0 − 5 ± 1 . 3 × 1 0 − 9, C ̄ 2, 2 = 1 . 24973 × 1 0 − 5 ± 1 . 2 × 1 0 − 9 ) confirms previous estimates to better than 0.4% and, therefore, inferences about Mercury's moment of inertia and interior structure. Our estimate of the tidal Love number k 2 = 0.464 ± 0.023 indicates that Mercury's mantle may be hotter and weaker than previously thought. Our spin state solution suggests that gravity‐based estimates of Mercury's spin axis orientation are marginally consistent with previous measurements of the orientation of the crust. Key Points: We estimated Mercury's gravity field, tidal Love number, and spin state based on more than 3 years of MESSENGER radio tracking data Our estimate of the Love number indicates that Mercury's mantle may be hotter and weaker than previously thought Our estimate of the spin state parameters indicates that the gravity field and crust rotate about nearly the same axis