Examinando por Autor "Hood, L. L."

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A New Large-Scale Map of the Lunar Crustal Magnetic Field and Its Interpretation
(Advancing Earth and Space Science AGU, 2021-02-23) Hood, L. L.; Torres, C. B.; Wieczorek, Mark A.; Stewart, S. T.; Oliveira, Joana S.; National Aeronautics and Space Administration (NASA)
A new large-scale map of the lunar crustal magnetic field at 30 km altitude covering latitudes from 65°S to 65°N has been produced using high-quality vector magnetometer data from two complementary polar orbital missions, Lunar Prospector and SELENE (Kaguya). The map has characteristics similar to those of previous maps but better resolves the shapes and distribution of weaker anomalies. The strongest group of anomalies is located on the northwest side of the South Pole-Aitken basin approximately antipodal to the Imbrium basin. On the near side, both strong isolated anomalies and weaker elongated anomalies tend to lie along lines oriented radial to Imbrium. These include named anomalies such as Reiner Gamma, Hartwig, Descartes, Abel, and Airy. The statistical significance of this tendency for elongated anomalies is verified by Monte Carlo simulations. Great circle paths determined by end points of elongated anomaly groups and the locations of five individual strong anomalies converge within the inner rim of Imbrium and intersect within the Imbrium antipode zone. Statistically significant evidence for similar alignments northwest of the Orientale basin is also found. The observed distribution of anomalies on the near side and the location of the strongest anomaly group antipodal to Imbrium are consistent with the hypothesis that iron from the Imbrium impactor was mixed into ejecta that was inhomogeneously deposited downrange in groups aligned radial to the basin and concentrated antipodal to the basin.
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Asymmetric Magnetic Anomalies Over Young Impact Craters on Mercury
(AGU, 2021-02-01) Galluzzi, V.; Wright, Jack; Rothery, D. A.; Hood, L. L.; Oliveira, Joana S.; National Aeronautics and Space Administration (NASA); Agenzia Spaziale Italiana (ASI); European Commission (EC)
Mercury's crustal magnetic field map includes anomalies that are related to impact craters. Mercury's surface has a low iron abundance, but it is likely that some impactors brought magnetic carriers able to register the planet's magnetic field that was present during impact. Anomalies associated with the relatively young Rustaveli and Stieglitz craters are asymmetric with respect to the crater center. We analyze the location of the magnetic anomalies and the impact crater morphologies to understand whether there is any correlation. We investigate the geological framework of these two craters to constrain the overall impact dynamics. In both cases, magnetic anomalies correlate well with the location of impact melt and the inferred impact direction. Both impact angles were probably 40°–45°, with preferential distribution of the melt downrange. Inversion dipoles suggest that the impact melt located downrange encompasses some magnetized material, which is hence likely responsible for the detected magnetic anomalies. We observe strong crustal magnetic field imprints near two recent craters on Mercury. We know that the crust of rocky planets may include magnetic elements like iron that can record the local magnetic field under certain circumstances. However, Mercury's crust is known to be remarkably poor in iron. In this study, we want to find out whether these observed magnetic imprints near craters happened by chance or if it can be explained by the impactors bringing iron to Mercury's surface. We make a joint-study of two different scientific areas: Geology and geophysics. Via the geological study, we found an uneven distribution of “impact melt,” which is material flung out of the crater in molten form during the impact that made the crater. Via the geophysical study, we found evidence that magnetized material correlates with the position of those pools that are found in the downrange direction of the impact. In conclusion, this study supports the hypothesis that iron was brought on Mercury by the impactors.
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Magnetic Anomalies in Five Lunar Impact Basins: Implications for Impactor Trajectories and Inverse Modeling
(Advancing Earth and Space Science AGU, 2020-12-30) Hood, L. L.; Andrews Hanna, J. J.; Wieczorek, Mark A.; Stewart, S. T.; Oliveira, Joana S.; National Aeronautics and Space Administration (NASA)
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.