A new view on the solar wind interaction with the Moon

Abstract

Characterised by a surface bound exosphere and localised crustal magnetic fields, the Moon was considered as a passive object when solar wind interacts with it. However, the neutral particle and plasma measurements around the Moon by recent dedicated lunar missions, such as Chandrayaan-1, Kaguya, Chang'E-1, LRO, and ARTEMIS, as well as IBEX have revealed a variety of phenomena around the Moon which results from the interaction with solar wind, such as backscattering of solar wind protons as energetic neutral atoms (ENA) from lunar surface, sputtering of atoms from the lunar surface, formation of a "mini-magnetosphere" around lunar magnetic anomaly regions, as well as several plasma populations around the Moon, including solar wind protons scattered from the lunar surface, from the magnetic anomalies, pick-up ions, protons in lunar wake and more. This paper provides a review of these recent findings and presents the interaction of solar wind with the Moon in a new perspective.

Surface Water at Lunar Magnetic Anomalies

“…Some anomalies may have acquired their magnetization from fields related to plasmas from large impacts of similarly old age (Hood & Artemieva, ). Regardless of their origin, the Moon's strongest magnetic anomalies likely reduce the surface solar wind flux (Bhardwaj et al, ; Deca et al, ; Hood & Schubert, ), as evidenced by reflection of solar wind observed at high altitudes by Chandrayaan‐1 (e.g., Barabash et al, ; Bhardwaj et al, ; Lue et al, ). This interpretation is also supported by the apparent reduction in local space weathering, leading to sinuous bright surface markings, known as swirls (Blewett et al, ; Hemingway & Garrick‐Bethell, ; Poppe et al, ).…”

Transport of solar wind plasma onto the lunar nightside surface

“…In recent years, the lunar dayside surface was proven to be very effective in neutralizing and reflecting impinging solar wind plasma: Up to 20% of the impinging solar wind protons are neutralized upon interaction with the lunar surface before being reflected back to space as hydrogen energetic neutral atoms (ENAs) [e.g., McComas et al , ; Wieser et al , ; Vorburger et al , ; Bhardwaj et al , ]. ENA imaging thus provides a powerful tool to investigate the solar wind plasma interaction process with the lunar surface.…”

New suprathermal proton population around the Moon: Observation by SARA on Chandrayaan‐1

“…Upon interaction with the lunar regolith, the solar wind protons backscatter as energetic neutral hydrogen atoms (H ENA ) with a reflection ratio of 10-20% [McComas et al, 2009;Wieser et al, 2009;Vorburger et al, 2013;Bhardwaj et al, 2015]. These lunar H ENA with energies almost 50% of that of solar wind travel to space without any perturbation.…”