Protons in the near-lunar wake observed by the Sub-keV Atom Reflection Analyzer on board Chandrayaan-1

Abstract

Significant proton fluxes were detected in the near wake region of the Moon by an ion mass spectrometer on board Chandrayaan-1. The energy of these nightside protons is slightly higher than the energy of the solar wind protons. The protons are detected close to the lunar equatorial plane at a $140^{\circ }$ solar zenith angle, i.e., ~50${}^{\circ }$ behind the terminator at a height of 100 km. The protons come from just above the local horizon, and move along the magnetic field in the solar wind reference frame. We compared the observed proton flux with the predictions from analytical models of an electrostatic plasma expansion into a vacuum. The observed velocity was higher than the velocity predicted by analytical models by a factor of 2 to 3. The simple analytical models cannot explain the observed ion dynamics along the magnetic field in the vicinity of the Moon.

28 pages, 7 figures

References in corpus (2)

• First observation of a mini-magnetosphere above a lunar magnetic anomaly using energetic neutral atoms
• Dynamics of solar wind protons reflected by the Moon

Cited by in corpus (5)

• Mini-magnetospheres above the lunar surface and the formation of lunar swirls
• A new view on the solar wind interaction with the Moon
• Proton entry into the near-lunar plasma wake for magnetic field aligned flow
• Characteristics of proton velocity distribution functions in the near-lunar wake from Chandrayaan-1/SWIM observations
• Near-lunar proton velocity distribution explained by electrostatic acceleration