Extremely high reflection of solar wind protons as neutral hydrogen atoms from regolith in space
Barabash, Stas; Holmström, Mats; Futaana, Yoshifumi; Wieser, Martin; Asamura, Kazushi; Wurz, Peter; Bhardwaj, Anil; Sridharan, R.; Dhanya, M. B.; Schaufelberger, Audrey
Sweden, India, Switzerland, Japan
Abstract
We report on measurements of extremely high reflection rates of solar wind particles from regolith-covered lunar surfaces. Measurements by the Sub-keV Atom Reflecting Analyzer (SARA) instrument on the Indian Chandrayaan-1 spacecraft in orbit around the Moon show that up to 20% of the impinging solar wind protons are reflected from the lunar surface back to space as neutral hydrogen atoms. This finding, generally applicable to regolith-covered atmosphereless bodies, invalidates the widely accepted assumption that regolith almost completely absorbs the impinging solar wind.