TY - JOUR
T1 - Magnetic Anomalies in Five Lunar Impact Basins
T2 - Implications for Impactor Trajectories and Inverse Modeling
AU - Hood, L. L.
AU - Oliveira, J. S.
AU - Andrews-Hanna, J.
AU - Wieczorek, M. A.
AU - Stewart, S. T.
N1 - Funding Information: Supported at the University of Arizona by grant 80NSSC18K1602 from the NASA Lunar Data Analysis Program. Lunar Prospector calibrated magnetometer data are available from the Planetary Plasma Interactions node of the NASA Planetary Data System ( https://pds-ppi.igpp.ucla.edu ). Kaguya (SELENE) vector magnetometer data are available from the Japan Aerospace Exploration Agency (JAXA) at http://darts.isas.jaxa.jp/planet/pdap/selene . The shaded relief maps with Lunar Orbiter Laser Altimeter data superposed used in the construction of several figures are available from the U.S. Geological Survey in Flagstaff, Arizona ( https://astrogeology.usgs.gov/search/map/Moon/LMMP/LOLA-derived/Lunar_LRO_LOLA_ClrShade_Global_128ppd_v04 ). The large‐scale field map at 30 km altitude shown in Figure S1 (from Hood et al., 2021 ), including the three vector field components as well as the field magnitude is available for download from the Planetary Plasma Interactions node of the NASA Planetary Data System at UCLA (Hood et al., 2020 ; https://doi.org/10.17189/1520494 ). Publisher Copyright: © 2020. American Geophysical Union. All Rights Reserved.
PY - 2021/2
Y1 - 2021/2
N2 - A recent large-scale map of the lunar crustal magnetic field is examined for the existence of magnetic anomalies internal to ringed impact basins. It is found that, of 25 basins with upper preNectarian and younger ages, 18 contain mapped internal anomalies with amplitudes of at least 1 nT at 30 km altitude. Of these, five are most confidently judged to contain intrinsic anomalies (i.e., anomalies located within the inner basin rims and originating at the times of basin formation): Crisium, Humboldtianum, Mendel-Rydberg, Moscoviense, and Nectaris. Comparing the anomaly distributions with previous numerical simulations of the impact of iron-rich planetesimals to form a large (SPA-sized) basin, inferences are drawn about the likely trajectories of the impactors. Specifically, results suggest that impactor trajectories for these basins were within ∼45° of being vertical and tended to lie on average parallel to the lunar equatorial plane and the ecliptic plane. Inverse modeling of anomalies within these basins yields inferred directions of magnetization that are difficult to reconcile with the axial centered dipole hypothesis for the geometry of the internal lunar dynamo field: Paleomagnetic pole positions are widely scattered and, in agreement with a recent independent study, the two main anomalies within Crisium yield significantly different directions of magnetization.
AB - A recent large-scale map of the lunar crustal magnetic field is examined for the existence of magnetic anomalies internal to ringed impact basins. It is found that, of 25 basins with upper preNectarian and younger ages, 18 contain mapped internal anomalies with amplitudes of at least 1 nT at 30 km altitude. Of these, five are most confidently judged to contain intrinsic anomalies (i.e., anomalies located within the inner basin rims and originating at the times of basin formation): Crisium, Humboldtianum, Mendel-Rydberg, Moscoviense, and Nectaris. Comparing the anomaly distributions with previous numerical simulations of the impact of iron-rich planetesimals to form a large (SPA-sized) basin, inferences are drawn about the likely trajectories of the impactors. Specifically, results suggest that impactor trajectories for these basins were within ∼45° of being vertical and tended to lie on average parallel to the lunar equatorial plane and the ecliptic plane. Inverse modeling of anomalies within these basins yields inferred directions of magnetization that are difficult to reconcile with the axial centered dipole hypothesis for the geometry of the internal lunar dynamo field: Paleomagnetic pole positions are widely scattered and, in agreement with a recent independent study, the two main anomalies within Crisium yield significantly different directions of magnetization.
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U2 - 10.1029/2020JE006668
DO - 10.1029/2020JE006668
M3 - Article
SN - 2169-9097
VL - 126
JO - Journal of Geophysical Research: Planets
JF - Journal of Geophysical Research: Planets
IS - 2
M1 - e2020JE006668
ER -