The High-Energy Neutron Detector (HEND) is part of he Mars Odyssey Gamma-Ray Spectrometer suite.
    The chief scientific objectives of the HEND instrument is 
    to map the near surface hydrogen (and, by inference, water) and
    CO2 abundances and their stratigraphic distributions, and
    determine their seasonal variations, and to determine the depth of the seasonal polar caps and their
    variation with time.