Observation of the γ-ray emission from the martian surface by the APEX experiment

The study of gamma-ray emission from planets with a thin atmosphere allows a rough estimation of the chemical composition of their surfaces to be made. Here, results from the gamma-ray APEX experiment on board Phobos 2 are presented. The measured gamma-ray albedo of the Martian surface appears as a large continuum between a few hundred keV and 8 MeV corresponding to a source intensity of 5 photons/sq cm/s/2 pi. There is also evidence for a 511-keV annihilation emission and for a broad contribution of probable nuclear lines between 4 and 7 MeV. (C.D.)