APL Colloquium

February 9, 2007

Colloquium Topic: What Lies Beneath? Using Radar to Look Below the Surface of the Moon and Mars

The geologic histories of the Moon and planets are recorded in their landforms and surface deposits. Remote sensing observations from the Earth or orbiting spacecraft provide a synoptic view of geologic features, and with improved instruments can reveal even fine details. What is often lacking, however, is the ability to see beneath the visible surface to understand the thickness and compositional variations in weathered layers, trace the distribution of rocky debris scattered by impacts and other processes, and to map potentially ancient features now buried by sediments. This three-dimensional context becomes more important as we plan for excavation of resource-bearing lunar material or samples from Mars that may contain a record of past climate or life. Radar remote sensing offers the capability to probe meters to kilometers beneath the surface of a planet. Two recent applications, high-resolution synthetic aperture radar mapping of the Moon and deep radar sounding of Mars, are illustrated in this talk. New maps of the Moon's near side at 70-cm wavelength, and targeted 20-m resolution images at 12.6-cm wavelength, reveal previously unseen variations in deposits related to the impacts that carved out great basins and sculpted the upper kilometers of the lunar landscape. Penetrating as much as 50 m into the dry lunar soil, the 70-cm signals also trace the extent of ancient lava flows now buried beneath basin-derived ejecta. The SHARAD radar sounder on the Mars Reconnaissance Orbiter has begun to reveal subsurface layers to depths of 1-2 km. Together, these studies provide a new window on the near-surface geology of the Moon and Mars, and point the way toward future radar remote sensing of the planets.

Colloquium Speaker: Bruce Campbell

Bruce Campbell received his B.S. in Geophysics from Texas A&M University in 1986, and his Ph.D. in Geology and Geophysics from the University of Hawaii in 1991. He joined the Smithsonian's Center for Earth and Planetary Studies in 1992. From 1996 to 1998, he was the Discipline Scientist for NASA's Planetary Instrument Definition and Development Program. He served as CEPS Chairman from 1998 until 2002. Dr. Campbell's research interests focus on applications of radar remote sensing to the understanding of volcanism, impact cratering, weathering, and other geologic processes on the terrestrial planets. This work includes collection of new radar data using spacecraft and Earth-based radio telescopes, development of methods for extracting geologic information from polarimetric scattering properties, and model validation through terrestrial remote sensing and fieldwork. Recent accomplishments include producing a nearly complete map of the Moon's near side at 70-cm wavelength, development of a focusing method to yield 20-m resolution lunar radar images at 12.6-cm wavelength, and completion of two USGS Venus geologic maps. Dr. Campbell is also a team member for the SHARAD shallow radar sounder on the 2005 Mars Reconnaissance Orbiter, which probes the martian crust to identify geologic layering and possible water or ice deposits.