First Observation of Transport of Solar Wind Protons Scattered From Magnetic Anomalies Into the Near Lunar Wake: Observations by SARA/Chandrayaan‐1

Abstract

We report the first observational evidence for the transport of the solar wind protons scattered from the lunar magnetic anomaly (LMA) into the near wake region from SWIM/Sub‐keV Atom Reflecting Analyzer (SARA) aboard Chandrayaan‐1. These protons with high angular spread are observed in the near wake region for specific orientations of interplanetary magnetic field. The typical energy range is 600–1,000 eV, which is either smaller or comparable to that of solar wind. Using our backtracing model, the source region of these protons is found to be the large LMA at South Pole‐Aitken basin on the dayside, suggesting that these are solar wind protons forward scattered from LMA at the South Pole‐Aitken. The flux of these protons is ∼5 × 10−4 of the solar wind proton flux, which is comparable to the proton population in near wake due to other known processes. Such protons can significantly affect the electromagnetic environment in near wake region.

Particles and Photons as Drivers for Particle Release from the Surfaces of the Moon and Mercury

“…The reflected ions from lunar crustal magnetic fields and the backscattered ions from lunar surface interact with the ambient electromagnetic environment and the upstream plasma and generate a broad range of plasma waves from ∼0.01-0.1 Hz narrowband ULF (Nakagawa et al 2012;Halekas et al 2013) to ∼0.1-10 Hz broadband whistlers (Halekas et al 2008aNakagawa et al 2011;Tsugawa et al 2012) and narrowband whistlers from ∼1 Hz up to ∼100 Hz (e.g., Lin et al 1998;Halekas et al 2006Halekas et al , 2008aTsugawa et al 2011Tsugawa et al , 2012Harada et al 2014b). Some of these reflected ions are "picked-up" and move into the lunar wake and they may impact the lunar nightside (e.g., Nishino et al 2009b;Dhanya et al 2018). However, the flux of these ions is expected to be very low, thus they have a minor contribution in the surface sputtering on the nightside.…”

Linear analysis of electrostatic waves in the lunar wake plasma

“…The wake region of moon, commonly called as lunar wake, is an interesting natural laboratory to study various types of plasma waves and related phenomenon. This wake region is formed by the interaction of moon with the solar wind impinging on its surface [1][2][3]. Early studies of moon were conducted by Dolginov et al [4,5] using Luna 1 and Luna 2 satellites.…”