![halo 3 standoff halo 3 standoff](https://i.ytimg.com/vi/vtCarbWmm5A/maxresdefault.jpg)
Locally the surface is shielded from up to 80% of the incoming solar wind plasma, while simultaneously protons are focused into the ‘cusp’ regions. Hence, the early two-dipole models 25 are a good first-order approximation for the Reiner Gamma magnetic field region. 1b) emerges, to first order, as the superposition of two horizontal dipoles/mini-magnetosphere structures 17, and does not show any structural differences compared to the input magnetic field model. The reflected proton fluxes predicted by our fully kinetic simulations are in excellent agreement with in-orbit flux measurements from the Sub-keV Atom Reflecting Analyzer–Solar Wind Monitor (SARA-SWIM) ion sensor onboard the Chandrayaan-1 mission, reassuring that a kinetic approach to describe the solar wind interaction with LMAs is vital.Īt steady state, the simulated proton charge–density pattern of Reiner Gamma at the surface (Fig. The weathering profile generated by the latter quantity matches best the surface reflectance pattern observed by the Lunar Reconnaissance Orbiter–Wide Angle Camera (LRO-WAC). The magnitude, direction, and shape of the charge-separation electric field are the key ingredients that regulate the proton energy flux to the surface. In this work, we show that solar wind standoff explains the correlation between the lunar surface albedo patterns and LMAs. Our simulation addresses only solar wind standoff, as the other suggested mechanisms fall outside the current capabilities of self-consistent plasma simulation tools. We implement the three-dimensional (3-D) geometry and topology of the lunar crustal magnetic field using an open source Surface Vector Mapping (SVM) model based on Kaguya and Lunar Prospector magnetic field measurements 24. Here we use the fully kinetic code, iPIC3D 23, which self-consistently resolves both the ion and electron dynamics. A fluid (magnetohydrodynamic) or hybrid (using a kinetic description for the ions but describing the electrons as a mass-less fluid) approach requires surface magnetic fields and/or spatial scales of at least an order of magnitude greater than what is at present day inferred from in-orbit observations to shield the underlying surface, form Reiner Gamma’s three bright lobes, and focus the solar wind plasma into its dark lanes 8, 22. The validity of the solar wind standoff model, however, cannot be determined through evaluating the magnetic topology and magnitude of the crustal field alone, as magnetic shielding on small scales is an ion–electron kinetic mechanism 17. If the surface weathering pattern generated by the solar wind interaction with the magnetic topology matches the observed albedo markings, it supports the formation of lunar swirls by solar wind standoff. The geometry of the magnetisation is believed to have a crucial role in reproducing the combination of dark lanes (believed to be areas where the crustal magnetic field has primarily vertical orientation with respect to the surface) and bright lobes (areas believed to have a more horizontal field orientation) of the Reiner Gamma swirl pattern 21, 22. Its tadpole-shaped albedo pattern consists of two dark lanes surrounded by the inner and outer bright lobes. Reiner Gamma’s magnetic topology produces a mini-magnetosphere 15, 16 that locally shields the lunar surface from impinging solar wind plasma 17, 18, 19, 20. Three possible formation mechanisms are currently discussed in the literature: (1) recent cometary and micrometeoroid impacts might have left behind remnant magnetisation and fine-grained, unweathered material that locally brightens the surface 5, 6, 7 (2) solar wind standoff due to the presence of lunar magnetic anomalies (LMAs), locally preventing weathering by solar wind ions and the subsequent formation of nanophase iron (np-Fe 0) that darkens the regolith 2, 8, 9, 10, 11, 12, 13 and (3) magnetic sorting of electrostatically levitated high-albedo, fine-grained, feldspar-enriched dust 13, 14. The evolutionary scenario of the lunar albedo markings has been under debate since the Apollo era 4. All known swirls are co-located with magnetic anomalies, but the opposite does not hold 2, 3. Observations have shown that the tadpole-shaped albedo marking, or swirl, is co-located with one of the strongest crustal magnetic anomalies on the Moon 1. Discovered by early astronomers during the Renaissance, the Reiner Gamma formation is a prominent lunar surface feature.