Planetary gamma-ray spectroscopy of the surface of Mercury

To approach basic scientific questions on the origin and evolution of Mercury one needs data on its chemical composition. Gamma-rays emitted from the surface can be measured by a gamma-ray spectrometer on board an orbiting spacecraft. The gamma-ray flux emitted by the surface of Mercury is simulated by Monte-Carlo codes that calculate the interaction of cosmic-ray particles with the surface and the subsequent gamma-ray production. Different surface compositions are assumed for these calculations. The calculated gamma-ray data allow a clear distinction of the different surface compositions. Also, the ability to detect water buried in the polar zones is taken into consideration: small amounts of water will be seen in the gamma-ray data. Applying the Monte-Carlo technique in an iterative process, measured gamma-ray data can be converted into elemental concentrations of many elements present in the surface. A detector with excellent energy resolution is required to fully exploit the complex gamma-ray spectra. A cooled germanium detector would be the best choice for this task, provided constraints on mass and power can be solved in the near future.