Lunar Swirl Morphology Constrains the Geometry, Magnetization, and Origins of Lunar Magnetic Anomalies


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August 2018


Lunar swirls are collections of finely structured bright and dark surface markings, alternating over length scales of typically 1–5 km. If swirls are the result of plasma interactions with crustal magnetic anomalies or electrostatic or magnetic sorting of fine materials, the magnetic field orientation must vary over similar length scales. This requires that the associated source bodies be both shallow and narrow in horizontal extent. The correspondingly restricted volume of the source bodies in turn implies strong rock magnetization. Here we show that if ∼300‐nT surface fields are necessary to produce observable swirl markings, the required rock magnetization must be >0.5 A/m, even for very shallow sources and likely closer to ∼2 A/m or more. This strong source rock magnetization, together with the geometric constraints that favor magmatic structures such as dikes or lava tubes, requires a mechanism to enhance the magnetic carrying capacity of the rocks. We propose that heating associated with magmatic activity could thermochemically alter host rocks and impart them with magnetizations an order of magnitude stronger than is typical of lunar mare basalts. Our results both place constraints on the geometry and magnetization of the source bodies and provide clues about the possible origins of the Moon's crustal magnetic anomalies.


Lunar Magnetic Anomalies, Lunar Swirls, Magnetic Field Topology, Lava Tubes Magnetization, Dikes

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Journal of Geophysical Research: Planets, Vol. 123, no. 8 (2018-08-01).