GEODETIC CLUES IN PLANETARY TREASURE HUNTS

Abstract:

Understanding the dynamics and evolution of terrestrial planetary bodies requires the synthesis of many observables of varying quality and spatial and temporal sampling. Geodetic-quality gravity and topography acquired by orbiting spacecraft provide essential clues in solving planetary puzzles. Collectively these data sets provide a precise reference frame, increasing the value of all other datasets, both remote and in situ. Gravity and topography are fundamental measurements that also provide critical insights in their own right; the advent of highly precise, geodetically-referenced datasets resulted in an extraordinary advance in understanding the constitution and evolution of planets. On Mars, the change in data quality from Viking to Mars Global Surveyor represented a transition from low-resolution topographic models with the wrong pole high to the ability to measure both the height and mass of seasonal (CO₂) snowfall, before such measurements were made by terrestrial satellites of Earth. The ultra-challenging thermal environment at Mercury precluded uniformly-sampled, global high-resolution datasets in the MESSENGER mission due to the spacecraft’s elliptical orbit, but the combination of orbital geodetic and Earth-based radar data supplemented by remote sensing observations of surface composition led to novel models for the nature of the planet’s core. At the Moon the combination of high-resolution topographic data from the Lunar Orbiter Laser Altimeter (LOLA) on the Lunar Reconnaissance Orbiter spacecraft with gravity from the dual-spacecraft Gravity Recovery and Interior Laboratory spacecraft enabled, for the first time on a planetary body beyond Earth, geophysics at the spatial scale of geology, and provided observations of pervasive impact-induced fracturing of the lunar crust, and the presence of massive subsurface dikes that pointed to a hypothesized but previously undetected thermal expansion of the Moon. Demonstration of critical technologies for precise measurement of gravity and topography open the possibility of future extraordinary discoveries in the inner and outer solar system.