Mars Express/ASPERA-3/NPI and IMAGE/LENA Observations Downstream of the Heliospheric Neutral Atom Flow

Both in cruise phase and at Mars, the neutral particle instrument NPD on Mars Express observed "unexplained neutral beams" (e.g. Barabash, EOS Trans, AGU, 85(47), Fall Meeting Suppl., Ab. SH43A-1092, F1509-1510) unrelated to Mars which appear to be either heliospheric or of solar wind origin. Independently, IMAGE/LENA has reported neutral atom observations that may be interpreted as a "secondary stream" having different characteristics and flowing from a higher ecliptic longitude than the nominal upstream direction (e.g. Collier et al., Adv. Space Res., 34, 166-171, 2004; Wurz et al., AIP Conf. Proceedings 719, 195-200, 2004). Both sets of observations do not appear to fit in easily with the neutral atom environment from 1.0-1.5 AU as it is currently understood. In this presentation we compare IMAGE/LENA data with Mars Express/ASPERA-3/NPI data taken during eclipse season to try to understand both data sets better.