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Chandrayaan‐1 observations of backscattered solar wind protons from the lunar regolith: Dependence on the solar wind speed
Author(s) -
Lue Charles,
Futaana Yoshifumi,
Barabash Stas,
Wieser Martin,
Bhardwaj Anil,
Wurz Peter
Publication year - 2014
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
eISSN - 2169-9100
pISSN - 2169-9097
DOI - 10.1002/2013je004582
Subject(s) - regolith , solar wind , wind speed , physics , proton , backscatter (email) , flux (metallurgy) , computational physics , atmospheric sciences , astronomy , meteorology , plasma , materials science , nuclear physics , telecommunications , computer science , metallurgy , wireless
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 ~0.01% to ~1% for solar wind speeds of 250 km/s to 550 km/s. We also study the speed distribution of the backscattered protons in the fast (~550 km/s) solar wind case and find both a peak speed at ~80% of the solar wind speed and a spread of ~85 km/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.