First Observation of Transport of Solar Wind Protons Scattered From Magnetic Anomalies Into the Near Lunar Wake: Observations by SARA/Chandrayaan‐1. Issue 17 (14th September 2018)

• Record Type: Journal Article
• Authors: Dhanya, M. B.; Bhardwaj, Anil; Alok, Abhinaw; Futaana, Yoshifumi; Barabash, Stas; Wieser, Martin; Holmström, Mats; Wurz, Peter
• Is Part Of: Geophysical research letters. Volume 45:Issue 17(2018)
• Page Start: 8826
• Page End: 8833
• Publication Date: 2018-09-14
• Subjects: Moon -- lunar magnetic anomaly -- solar wind -- near wake -- Chandrayaan‐1 SARA/SWIM -- IMF; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2018GL079330
• Languages: English
• ISSNs: 0094-8276

Abstract

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. Plain Language Summary: The understanding of solar wind interaction with the Moon and the ensuing plasma dynamics are still evolving. The near lunar wake refilling by solar wind protons are a recent discovery, and a few processes are now known to play a role. The small‐scale crustal magnetic fields on the Moon can also cause scattering of the impinging solar wind protons back to space. This paper shows for the first time that solar wind protons scattered from lunar magnetic regions on dayside can get transported to the nightside of the Moon, thereby contributing an additional process of plasma refilling in the near wake region. The results have direct applications to near lunar plasma environment and to any atmosphere‐less body with no global magnetic field, such as asteroids and several planetary satellites. The findings have impact on space plasma physics, as well as lunar and planetary science communities. Key Points: First observation on transport of solar wind protons scattered from lunar magnetic anomaly into the near wake region Forward scattering by magnetic anomaly at South Pole‐Aitken basin for high solar zenith angle The flux is estimated to be ∼5 × 10 ‐4 of the solar wind proton flux