Chandrayaan-1 observations of backscattered solar wind protons from the lunar regolith : Dependence on the solar wind speed

• We study the backscattering of solar wind protons from the lunar regolith using the Solar Wind Monitor of the Sub-keV Atom Reflecting Analyzer on Chandrayaan-1. Our study focuses on the component of the backscattered particles that leaves the regolith with a positive charge. We find that the fraction of the incident solar wind protons that backscatter as protons, i.e., the proton-backscattering efficiency, has an exponential dependence on the solar wind speed that varies from similar to 0.01% to similar to 1% for solar wind speeds of 250km/s to 550km/s. We also study the speed distribution of the backscattered protons in the fast (similar to 550km/s) solar wind case and find both a peak speed at similar to 80% of the solar wind speed and a spread of similar to 85km/s. The observed flux variations and speed distribution of the backscattered protons can be explained by a speed-dependent charge state of the backscattered particles.

Subject headings

NATURVETENSKAP  -- Fysik -- Fusion, plasma och rymdfysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Fusion, Plasma and Space Physics (hsv//eng)

Keyword

Moon

proton

backscatter

regolith

Publication and Content Type

ref (subject category)

art (subject category)