35. Advances in Planetary Radar Astronomy

During an era when observations from spacecraft have produced the great majority of new information about the solar system, observations of solar-system bodies from the Earth, using high-powered radar systems, have produced some remarkable results. These include the discovery of condensed volatiles, most likely water ice, at the poles of Mercury; the high-resolution imaging of main-belt and near-Earth asteroids, including the discovery of the first near-Earth asteroid binary systems; the discovery of cm-sized grains in the comas of comets; the investigation of the radio-wavelength scattering properties of the surface of Titan; and measurements of the topography of the lunar polar regions at high spatial and altitude resolutions. Multi-wavelength measurements of the scattering properties of the icy Galilean satellites of Jupiter have elucidated some of the properties of their upper surface layers, while measurements of the polarization properties of the echoes from planets, satellites, and small bodies have provided information about their wavelength-scale roughness properties.