Abstract:
Our knowledge of the planet Mercury has increased drastically during the past few years due to repeated measurements of Mercury's rotation rate to 1 part in 10 5 and the determination of the orientation of the spin axis to 6 arcsec from a ground based radar experiment and from three close flybys of the MESSENGER spacecraft. I will show you how the radar measurements are made and how we used the information so obtained to infer that Mercury has at least a partially molten core. During the orbiting phase of the MESSENGER mission beginning on March 18, 2011, we hope to (1) constrain the planetary formational processes that led to the high metal-to-silicate ratio in Mercury, (2) constrain the geologic history, (3) determine the nature and origin of Mercury's magnetic field, (4) determine the state and structure of Mercury's core and thereby infer the thermal history, (5) determine the nature of the radar reflective material at Mercury's poles, and (6) determine the important volatile species and their sources and sinks on or near Mercury. In the meantime, the three flybys have already led to exciting discoveries on Mercury's fault structures, volcanism and magmatism, shape, molten core, magnetic field and interaction with the solar wind.