Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p41c1628h&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P41C-1628
Physics
[1517] Geomagnetism And Paleomagnetism / Magnetic Anomalies: Modeling And Interpretation, [2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions, [5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
"Swirls" are peculiar, sinuous patterns of anomalously high albedo that accompany many of the Moon's crustal magnetic anomalies. These enigmatic surface features are at the intersection of many important questions in lunar science, ranging from space weathering [1] to the long-term thermal evolution of the Moon (e.g. did the Moon possess a core dynamo?), to dust levitation [1], to the generation of hydroxyl molecules within the Moon's upper regolith [2]. The solar wind standoff hypothesis [3] suggests that local magnetic fields deflect incoming solar wind particles at swirls, preventing them from weathering and darkening portions of the surface. Here we test the solar wind standoff hypothesis by examining the relationship between albedo and the orientation of the local magnetic field. If magnetic deflection of solar wind particles is indeed the primary mechanism for swirl formation, the orientation of the magnetic field should be important. Since the Lorentz force is maximized when the motion of charged particles is perpendicular to the magnetic field lines, incoming particles should be deflected most significantly where the field lines are perpendicular to the solar wind. Using Lunar Prospector data, we separately examine the horizontal (perpendicular to the solar wind at noon) and radial components of the magnetic field at Reiner Gamma. We find a positive correlation between magnetic field strength and albedo that is much more pronounced for the horizontal component than for the radial (see figure), suggesting that in swirl formation, the horizontal component is substantially more important than the radial. Although the solar wind incident angle changes throughout the lunar day, the difference between horizontally and vertically oriented fields should still be important given that half the flux of solar wind particles is concentrated within 30 degrees of solar noon. Although a more comprehensive investigation remains to be completed, these results are consistent with the solar wind standoff hypothesis and begin to shed light on the importance of magnetic field orientation in the formation of swirls.
Garrick-Bethell Ian
Hemingway D.
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