Tailward flow of energetic neutral atoms observed at Venus
Kallio, E.; Barabash, S.; Gunell, H.; Futaana, Y.; Grigoriev, A.; Wurz, P.; Galli, A.; HolmströM, M.; Fok, M. -C.; EkenbäCk, A.
Switzerland, United States, Sweden, Finland
Abstract
The Analyzer of Space Plasma and Energetic Atoms (ASPERA-4) experiment on Venus Express provides the first measurements of energetic neutral atoms (ENAs) from Venus. The results improve our knowledge on the interaction of the solar wind with a nonmagnetized planet and they present an observational constraint to existing plasma models. We characterize the tailward flow of hydrogen ENAs observed on the nightside by providing global images of the ENA intensity. The images show a highly concentrated tailward flow of hydrogen ENAs tangential to the Venus limb around the Sun's direction. No oxygen ENAs above the instrument threshold are detected. The observed ENA intensities are reproduced with a simple ENA model within a factor of 2, indicating that the observed hydrogen ENAs originate from shocked solar wind protons that charge exchange with the neutral hydrogen exosphere.