Backscattered energetic neutral atoms from the Moon in the Earth's plasma sheet observed by Chandarayaan-1/Sub-keV Atom Reflecting Analyzer instrument

Harada, Yuki; Futaana, Yoshifumi; Barabash, Stas; Wieser, Martin; Wurz, Peter; Bhardwaj, Anil; Asamura, Kazushi; Saito, Yoshifumi; Yokota, Shoichiro; Tsunakawa, Hideo; Machida, Shinobu (2014). Backscattered energetic neutral atoms from the Moon in the Earth's plasma sheet observed by Chandarayaan-1/Sub-keV Atom Reflecting Analyzer instrument. Journal of Geophysical Research: Space Physics, 119(5), pp. 3573-3584. AGU Publications 10.1002/2013JA019682

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We present the observations of energetic neutral atoms (ENAs) produced at the lunar surface in the Earth's magnetotail. When the Moon was located in the terrestrial plasma sheet, Chandrayaan-1 Energetic Neutrals Analyzer (CENA) detected hydrogen ENAs from the Moon. Analysis of the data from CENA together with the Solar Wind Monitor (SWIM) onboard Chandrayaan-1 reveals the characteristic energy of the observed ENA energy spectrum (the e-folding energy of the distribution function) ∼100 eV and the ENA backscattering ratio (defined as the ratio of upward ENA flux to downward proton flux) <∼0.1. These characteristics are similar to those of the backscattered ENAs in the solar wind, suggesting that CENA detected plasma sheet particles backscattered as ENAs from the lunar surface. The observed ENA backscattering ratio in the plasma sheet exhibits no significant difference in the Southern Hemisphere, where a large and strong magnetized region exists, compared with that in the Northern Hemisphere. This is contrary to the CENA observations in the solar wind, when the backscattering ratio drops by ∼50% in the Southern Hemisphere. Our analysis and test particle simulations suggest that magnetic shielding of the lunar surface in the plasma sheet is less effective than in the solar wind due to the broad velocity distributions of the plasma sheet protons.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences

UniBE Contributor:

Wurz, Peter

Subjects:

500 Science > 530 Physics

ISSN:

2169-9380

Publisher:

AGU Publications

Language:

English

Submitter:

Cléa Serpollier

Date Deposited:

15 Apr 2015 16:58

Last Modified:

16 Apr 2015 09:30

Publisher DOI:

10.1002/2013JA019682

BORIS DOI:

10.7892/boris.66762

URI:

https://boris.unibe.ch/id/eprint/66762

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