A Novel Bistatic Radar and Radiometer to Investigate Shallow Planetary Subsurfaces

The shallow subsurfaces of solar system bodies can hold important clues to their evolution, including their physical properties and the structure of buried geological features. Exploration of these regions can provide insight into possible habitable zones by revealing layering, discontinuities and the lateral variability of sedimentary materials. We propose a novel type of scientific instrument for studying shallow subsurfaces that uses radio communication systems on planetary missions to perform two types of investigations:

1) Bistatic radar measurements in which Earth-based radio antennas transmit a signal that is received by an existing radio communication antenna/receiver on a spacecraft. The receiver would detect interference patterns that are formed by the combination of direct signals from the Earth and signals scattered from the surface and subsurface. This measurement is sensitive to the dielectric properties of the subsurface materials and buried stratifications caused by past aqueous and non-aqueous processes.

2) Passive microwave radiometry measurements with the same onboard antenna/receiver to measure the lateral and temporal variations of ground brightness temperature. For example, temporal changes in ground temperature can identify the thermal inertia of subsurface material.

Such measurements could provide detailed information on the subsurface and geological context for surface measurements and sample collection. They could also motivate further investigations of interesting areas by other onboard instruments. We envision this type of instrument becoming a common feature on many future missions, perhaps with the scientific instrument functions built into the communication systems, thus providing key science at minimal additional cost and mass.