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We present observations of energetic neutral atoms (ENAs) in the shadow of Mars by the neutral particle imager (NPI), part of the ASPERA-3 experiment on-board Mars Express. The observations are well into the umbra, where the count rates are low, and contamination by UV light minimal. We present statistics over all available observations, from the 2004 and the early 2005 eclipse seasons. We investigate skymaps of the observations, and their time dependence, and try infer the dierent origins of the observed fluxes: instrumental eects, ENAs from Mars and its interaction with the solar wind, and ENAs of possibly heliospheric origin. We also study the time evolution of the observed signals. It is found that most of the observed emissions are consistent with UV, but some are not, suggesting ENA fluxes — Mars related and non-Mars related. The NPI measure the integral ENA flux (0.1‐60 keV) with no mass or energy resolution, but with high angular resolution (5 ◊ 11 degrees). The sensor is also sensitive to UV light.

OBSERVATIONS IN THE SHADOW OF MARS BY THE NEUTRAL PARTICLE IMAGER