17We report on measurements of extremely high reflection rates of solar wind 18 particles from regolith-covered lunar surfaces. Measurements by the Sub-keV 19 Atom Reflecting Analyzer (SARA) instrument on the Indian Chandrayaan-1 20 spacecraft in orbit around the Moon show that up to 20% of the impinging solar 21 wind protons are reflected from the lunar surface back to space as neutral 22 hydrogen atoms. This finding, generally applicable to regolith covered 23 -2 -atmosphereless bodies, invalidates the widely-accepted assumption that regolith 24 almost completely absorbs the impinging solar wind. 25 26 27 129 Sciences, 114 (No.6), 749-760 (2005) 130 Clark, B. E., B. Hapke, C. Pieters, D. Britt, Asteroid Space Weathering and Regolith 131 Evolution, Asteriods III, edts.

[1] The Sub-keV Atom Reflecting Analyzer (SARA) instrument on the Indian Chandrayaan-1 spacecraft has produced for the first time an image of a lunar magnetic anomaly in backscattered hydrogen atoms. The image shows that a partial void of the solar wind, a mini-magnetosphere, is formed above the strong magnetic anomaly near the Crisium antipode. The mini-magnetosphere is 360 km across at the surface and is surrounded by a 300-km-thick region of enhanced plasma flux that results from the solar wind flowing around the mini-magnetosphere. The minimagnetosphere is visible only in hydrogen atoms with energy exceeding 150 eV. Fluxes with energies below 100 eV do not show corresponding spatial variations. While the high-energy atoms result from the backscattering process, the origin of the low-energy component is puzzling. These observations reveal a new class of objects, minimagnetospheres, and demonstrate a new observational technique to study airless bodies, imaging in backscattered neutral atoms. Citation: Wieser, M., S. Barabash, Y. Futaana, M. Holmström, A. Bhardwaj, R. Sridharan, M. B. Dhanya, A. Schaufelberger, P. Wurz, and K. Asamura (2010), First observation of a mini-magnetosphere above a lunar magnetic anomaly using energetic neutral atoms, Geophys. Res. Lett., 37, L05103,

Abstract. Favored occurrences of Equatorial Counter Electrojets (CEJs) with a quasi 16-day periodicity over Trivandrum (8.5 • N, 76.5 • E, 0.5 • N diplat.) in association with the polar Stratospheric Sudden Warming (SSW) events are presented. It is observed that, the stratospheric temperature at ∼30 km over Trivandrum shows a sudden cooling prior to the SSWs and the CEJs of maximum intensity which occurs around this time. In general stronger CEJs are associated with more intense SSW events. The stratospheric zonal mean zonal wind over Trivandrum also exhibits a distinctly different pattern during the SSW period. These circulation changes are proposed to be conducive for the upward propagation of the lower atmospheric waves over the equatorial latitudes. The interaction of such waves with the tidal components at the upper mesosphere and its subsequent modification are suggested to be responsible for the occurrence of CEJs having planetary wave periods.

The Sub‐keV Atom Reflecting Analyzer instrument on board the lunar orbiter Chandrayaan‐1 provided a large number of measurements of lunar energetic neutral atoms (ENAs). These ENAs were formerly solar wind ions, which were neutralized and backscattered from the lunar surface. The angles under which the ENAs are scattered strongly depend on the solar wind ions' incidence angle, which corresponds to the solar zenith angle (SZA). Our large dataset provides us with a complete coverage of the SZA and almost complete coverage of the scattering angles. When combining all available measurements, four distinct features are discernible with SZA increase: amplitude decrease, less azimuthal uniformity, bigger ratio of sunward versus anti‐sunward flux and shallower scattering. We analyzed more than 290′000 measurements and derived a mathematical description of the features and their dependencies on the SZA.