Empirical energy spectra of neutralized solar wind protons from the lunar regolith

We present an empirical model of the energy spectra for hydrogen energetic neutral atoms (ENA) backscattered from the lunar surface based on Chandrayaan‐1 Energetic Neutral Atom (CENA) observations. The observed energy spectra of the backscattered ENAs are well reproduced by Maxwell‐Boltzmann distri...

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Bibliographic Details
Published in:Journal of Geophysical Research: Planets 2012-05, Vol.117 (E5), p.n/a
Main Authors: Futaana, Y., Barabash, S., Wieser, M., Holmström, M., Lue, C., Wurz, P., Schaufelberger, A., Bhardwaj, A., Dhanya, M. B., Asamura, K.
Format: Article
Language:English
Subjects:
Atmospheric sciences
backscattering
Comets
Earth sciences
Earth, ocean, space
energetic neutral atoms
Exact sciences and technology
hydrogen
Magnetism
Moon
Planetology
Planets
Plasma physics
regolith
Solar energy
solar wind
Space
Wind speed
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Summary:We present an empirical model of the energy spectra for hydrogen energetic neutral atoms (ENA) backscattered from the lunar surface based on Chandrayaan‐1 Energetic Neutral Atom (CENA) observations. The observed energy spectra of the backscattered ENAs are well reproduced by Maxwell‐Boltzmann distribution functions. The backscatter fraction is constant and independent of any solar wind parameters and the impinging solar wind angle. The calculated backscatter fraction is 0.19, and the 25% and 75% percentiles are 0.16 and 0.21. The empirical parameters of the Maxwell‐Boltzman distribution derived from the CENA imager have no correlations with the upstream solar wind parameters, except for a good correlation between the solar wind velocity and the temperature of the backscattered ENAs. These results suggest that the reflected ENAs have experienced several collisions during the interaction with the loose lunar grains, and are then released into space. The mathematical model of the energy spectra of the backscattered ENAs is expressed by a function of the solar wind flux and velocity, which can be used for future investigations of regolith‐solar wind interaction. Key Points We made empirical energy spectrum of lunar‐origin energetic neutral atoms The lunar‐origin energetic neutral atoms are backscattered solar wind protons The backscatter fraction is ~19% independent of upstream conditions
ISSN:0148-0227
2169-9097
2156-2202
2169-9100
DOI:10.1029/2011JE004019