Direct Measurements of Energetic Neutral Hydrogen in the Interplanetary Medium
Fedorov, A.; Barabash, S.; Lundin, R.; Holmström, M.; Gunell, H.; Futaana, Y.; Grigoriev, A.; Frahm, R. A.; Curtis, C. C.; Hsieh, K. C.; Cerulli-Irelli, R.; Wurz, P.; Bochsler, P.; Krupp, N.; Woch, J.; Winningham, D.; Galli, A.; Roelof, E. C.; Fraenz, M.
Switzerland, Sweden, United States, France, Italy, Germany
Abstract
We present an analysis of hydrogen energetic neutral atoms (ENAs) measured by the ASPERA-3 instrument on board Mars Express. We focus on ENAs that have no Martian origin. The energy spectra of these ENAs are all very similar and can be fitted well by a two-component power law. The fluxes, integrated from 0.2 to 10 keV, vary between 5×103 and 105 cm-2 sr-1 s-1. We checked for possible sources for these ENAs, but we can rule out a planetary origin, a solar wind origin, contamination by UV from UV bright stars, and contamination by high-energy protons. With our present knowledge we conclude that the heliospheric termination shock is the most plausible source region.