Kaguya observation of the ion acceleration around a lunar crustal magnetic anomaly

• We study an interaction between lunar crustal magnetic anomalies and the SW.
• We show an observation of ion acceleration around a magnetic anomaly.
• Low-energy ions due to the backscattering SW ions exist around magnetic anomalies.
• Magnetic anomalies deflect the IMF and produce an electric field in that condition.
• Our analyses show that backscattered SW ions are accelerated by the electric field.

We investigate Kaguya observation of ion acceleration around a lunar crustal magnetic anomaly located in the South Pole-Aitken basin at an altitude of 100 km. The accelerated ions in the 230 eV to 1.5 keV energy range were identified by a characteristic dispersion signature in the energy-time spectrogram that appeared repeatedly upon Kaguya׳s approach to the magnetic anomaly. The interplanetary magnetic field was almost parallel to the solar wind velocity and thus the electric field was very small. The results of our analysis show that ions with energies below 230 eV were accelerated up to 1.5 keV by an electric field produced by the interaction between the solar wind and the magnetic anomaly. We argue that the low-energy ions mainly originated from the solar wind ions with energies of 450 eV that were backscattered on the lunar surface.