Abstract: Size, shape and orientation are the fundamental quantities to provide insights into interiors and origins of planetary bodies. The interior structure of terrestrial planets can be effectively constrained, at long wavelength, by accurately measuring its gravity field, topography, rotation and orientation, and its potential body and surface tidal Love numbers, namely k₂ and h₂. One of the most important discoveries in radar astronomy during the 1960s is the quantification of the retrograde rotation of Venus and the nonsynchronous rotation of Mercury. These two planets are unique in their rotation (3:2 spin-orbit resonance with the Sun for Mercury, and in resonance with the Earth for Venus). Mercury also has the highest uncompressed density among the terrestrial planets, implying a large iron core, with a liquid outer layer. If we hypothesize that the Moon抯 body tides have detectable laterally variations, and that the lunar interior structure constraints would be improved with near global measurements of surface body tides instead of only the knowledge of the estimate or computation of a global h₂. For terrestrial bodies with possible presence of surface oceans underneath a planet-wide ice shell, e.g., namely k₂  Moon Triton, Jupiter抯 icy Moon Europa, Saturn抯 Moon Titan, etc., accurate estimating these parameters could place constraints on revealing the existence of surface oceans and quantify the thickness of the ice shells encircling these surface oceans. Asteroids such as Ceres and Vesta (NASA mission Dawn), S-type asteroid Itokawa (JAXA’s  Hayabusa-1 mission), the future C-Type asteroid162171 (1999 JU3 by JAXA’s  Hayabusa-2 mission), and the near-Earth, Apollo-type, spectral class B asteroid 101955 Bennu (NASA’s  asteroid sample return mission, OSIRIS-Rex), could all be studies for their respectiveinterior structure via the measurements of their gravity field, shape (topography), and rotations. Many of the satellite missions to these terrestrial bodies include geodetic sensors such as DSN tracking (or delta-VLBI tracking) or satellite-to-satellite tracking (GRAIL for the Moon) for measurements of gravity and tides, radar/laser altimeters/Lidars, or SAR/InSAR for topography measurements, and rovers or planet based observing stations and cameras for libration and body rotation measurements. Here we present scientific approaches for the combined use of these measurements towards constraining interior structure of the example terrestrial bodies.

C.K. Shum is a Professor and Distinguished University Scholar, Division of Geodetic Science, School of Earth Sciences, at The Ohio State University. He is a Fellow of the American Association for the Advancement of Science, and a Fellow of the International Association of Geodesy. He specializes in satellite geodesy, precision satellite orbit determination, temporal gravity field and tide modeling, and their cross-disciplinary science and applications to oceanography, hydrology, geodynamics, ice mass balance, GNSS meteorology and space physics. He has published over 241 refereed journal articles and book chapters.