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 interacti on of cosmic-ray particles with the surface and the subsequent gamma-r ay production. Different surface compositions are assumed for these ca lculations. 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 conv erted into elemental concentrations of many elements present in the su rface. A detector with excellent energy resolution is required to full y exploit the complex gamma-ray spectra. A cooled germanium detector w ould be the best choice for this task, provided constraints on mass an d power can be solved in the near future. (C) 1997 Elsevier Science Lt d.