P41C-2080
Planetary dynamics from laser altimetry: Spin and tidal deformation of the Moon and Mercury
Thursday, 17 December 2015
Poster Hall (Moscone South)
Michael Kenneth Barker, Sigma Space Corporation, Lanham, MD, United States, Erwan Mazarico, NASA Goddard Space Flight Center, Greenbelt, MD, United States, David E Smith, Massachusetts Institute of Technology, Cambridge, MA, United States and Maria T Zuber, Massachusetts Inst Tech, Cambridge, MA, United States
Abstract:
The dynamics of planetary bodies can provide valuable, and often unique, information on their interior structure. For instance, surface tidal deformation indicates how a body responds to the gravitational tidal forcing, and can thus give an indication of how the internal structure and temperature varies with depth. In addition, the orientation and spin rate of a planetary body are affected by its interior mass distribution and thermal evolution. In this contribution, we describe recent work to constrain the tidal deformation of the Moon and spin state and orientation of Mercury using altimetric crossovers measured by the Lunar Orbiter Laser Altimeter (LOLA) and MESSENGER Laser Altimeter (MLA). Altimetric crossovers are ideal for detecting the desired small surface changes, as they avoid the problem of aliasing topographic changes due to small-scale, unpredictable and uncorrelated, geologic relief. On the Moon, the tidal surface deformation is small (amplitude ~10 cm), but, using the highest quality LOLA crossovers, Mazarico et al. (2014) made the first measurement of the radial Love number h2 from an orbiting spacecraft. In a follow-up to that work, we are incorporating more crossovers to improve the temporal sampling of the tidal signal, thus enabling analysis of the spatial variation of the tidal amplitude, as might be expected given the thicker and cooler far side crust and the potential presence of a partial melt region below the PKT. Due to tidal torques from the Sun, Mercury experiences longitudinal librations about its 3:2 spin-orbit resonance with an amplitude of ~450 m at the equator. This amplitude is significantly larger than the geolocation uncertainty of the MLA altimetry (~10/100 m in radial/horizontal), and could, thus, be detectable from crossovers alone. However, given the sparse coverage near the equator, where the libration amplitude is largest, it may be necessary to incorporate into the analysis stereo-derived DEMs from the Mercury Dual Imaging System (MDIS).
