Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm33d..08s&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM33D-08
Physics
[2780] Magnetospheric Physics / Solar Wind Interactions With Unmagnetized Bodies, [5443] Planetary Sciences: Solid Surface Planets / Magnetospheres, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
It is well-known that the Moon has neither global intrinsic magnetic field nor thick atmosphere. Different from the Earth’s case where the intrinsic global magnetic field prevents the solar wind from penetrating into the magnetosphere, solar wind directly impacts the lunar surface. Since the discovery of the lunar crustal magnetic field in 1960s, several papers have been published concerning the interaction between the solar wind and the lunar magnetic anomalies including both numerical simulations and observation by lunar orbiters. MAG/ER on Lunar Prospector found heating of the solar wind electrons presumably due to the interaction between the solar wind and the lunar magnetic anomalies and the existence of the mini-magnetosphere was suggested. However, the detailed mechanism of the interaction has been unclear mainly due to the lack of the in-situ observed low energy ion data. MAgnetic field and Plasma experiment - Plasma energy Angle and Composition Experiment (MAP-PACE) on Kaguya (SELENE) completed its ˜1.5-year observation of the low energy charged particles around the Moon on 10 June 2009. MAP-PACE made observations at a circular lunar polar orbit of 100km altitude for about 1 year between January 2008 and December 2008. During the last 5 months, the orbit was lowered to ˜50km-altitude between January 2009 and April 2009, and some orbits had further lower perilune altitude of ˜10km after April 2009. When Kaguya flew over strong magnetic anomalies, deceleration of the solar wind ions, acceleration of the solar wind electrons, and ions reflected by magnetic anomalies were observed. The deceleration of the solar wind ions was observed for both two major solar wind ion components: protons and alpha particles. Deceleration of the solar wind had the same Δ E/q (Δ E : deceleration energy, q: charge) for both protons and alpha particles. In addition, the acceleration energy of the electrons was the same as the deceleration energy of the ions. It indicates the existence of DC electric field over Kaguya spacecraft. Since the gyro-radius of the electrons was smaller than the size of the magnetic anomalies, incident electrons were mirror reflected back. On the other hand, the gyro-radius of the ions was much larger than the size of the magnetic anomalies. Therefore the incident ions could penetrate deeper into the magnetic anomalies. As a result, DC electric field was generated over dayside magnetic anomalies. The reflected ions were observed in much larger area than the area where strong magnetic field was observed. Mass profile of the reflected ions showed existence of reflected alpha particles as expected from the magnetic mirror reflection. However, the energy of the reflected alpha particles was found to be lower than that of the alpha particles in the incident solar wind. In addition, the reflected protons also had lower energy and higher temperature than those of the incident solar wind protons. It clearly indicates the existence of a non-adiabatic interaction between solar wind ions and lunar magnetic anomalies.
Asamura Kazushi
Kaguya Map Team
Nishino Masaki N.
Saito Yukio
Tsunakawa Hideo
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