An improved crustal magnetic field map of Mars from electron reflectometry: Highland volcano magmatic history and the end of the martian dynamo |
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Authors: | Robert J Lillis Herbert V Frey David L Mitchell Mario H Acuña |
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Institution: | a UC Berkeley Space Sciences Laboratory, 7 Gauss Way, Berkeley, CA 94720, USA b NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA c UC Berkeley Department of Earth and Planetary Science, Berkeley, CA 94720, USA d University of Michigan Department of Atmospheric, Oceanic and Space Sciences, 2455 Hayward St., Ann Arbor, MI 48109-2143, USA |
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Abstract: | We apply improved kinetic modeling of electron transport in the martian thermosphere to fit pitch angle distributions measured by the Mars Global Surveyor (MGS) Magnetometer/Electron Reflectometer (MAG/ER), together with appropriate filtering, binning, averaging and error correction techniques, to create the most reliable ER global map to date of crustal magnetic field magnitude at 185 km altitude, with twice the spatial resolution and considerably higher sensitivity to crustal fields than global maps of magnetic field components produced with MAG data alone. This map compares favorably to sparsely sampled dayside MAG data taken at similar altitudes, insofar as a direct comparison is meaningful. Using this map, we present two case studies. The first compares the magnetic signatures of two highland volcanoes, concluding that the comparatively greater thermal demagnetization at Syrtis Major compared with Tyrrhena Patera is likely due to a higher ratio of intruded to extruded magmas. The second uses the map along with topographic data to compare the magnetic signatures and crater retention ages of the demagnetized Hellas impact basin and magnetized Ladon impact basin. From this comparison, we determine that the martian global dynamo magnetic field went from substantial to very weak or nonexistent in the absolute model age time interval 4.15±0.05 to 4.07±0.05 Ga ago. |
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Keywords: | Mars Magnetic fields Cratering Mars interior Volcanism |
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