| Institution(s) supplémentaire(s) | (1) Lunar and Planetary Lab, University of Arizona, Tucson, Arizona, USA 2) Space Magnetism Area, Payloads & Space Sciences Dept., Instituto Nacional de Tecnica Aerospacial, Torrejon de Ardoz, Spain (3) Instituto di Astrofisica e Planetologia Spaziali, Instituto Nazionale di Astrofisica, Rome, Italy (4) The Open University, Milton Keynes, U.K. (5) European Space Agency, ESAC (H/SCI-SCF), Madrid, Spain |
Abstract | We have previously reported mapping of MESSENGER magnetometer data at northern midlatitudes showing that crustal anomalies are strongest within and near the Caloris impact basin and also occur within and near a number of other Hermean impact craters and basins (Hood, GRL, 2015; JGR, 2016; Hood et al., JGR, 2018; Oliveira et al., JGR, 2019; Galluzzi et al., GRL, 2021). One hypothesis that is consistent with the observed anomaly distribution is that Hermean crustal magnetic sources consist mainly of impact melt and ejecta that was enriched in iron from impactors that created large basins and craters on Mercury. During cooling, these deposits would have acquired thermoremanent magnetization from the early Hermean core dynamo magnetic field. This hypothesis is based on previous work at the Moon dating from the post-Apollo period and continuing to recent improved mapping and interpretation of the lunar crustal field (Hood et al., JGR, 2021). Most of Mercury's original crust has been volcanically resurfaced over a period continuing until about 3.5 Gyr ago (e.g., Thomas and Rothery, Elements, 2019). Therefore, at least some iron-enriched impact melt and ejecta from basins such as Caloris may lie beneath these flows rather than at the surface. However, in the case of relatively young impact craters such as Rustaveli and Stieglitz, correlations of magnetic anomalies with the distribution of visible impact melt deposits have been found (Galluzzi et al., GRL, 2021).
Here, preliminary improved mapping of magnetic anomalies at 35 to 75 degrees north latitude on the Caloris side of Mercury is reported. Specifically, a denser equivalent source dipole array with a spacing of 0.5 degrees of latitude and 1 degree of longitude was applied to the cubic detrended MESSENGER magnetometer field measurements along the orbit tracks with a maximum passed wavelength of 20 degrees of latitude. The resulting higher-resolution map in polar stereographic projection shows that many anomalies, including that over the volcanic plain, Suisei Planitia, lie along lines oriented approximately radial to Caloris. Such radial alignments have also been recently found to exist south of the lunar Imbrium basin (Hood et al., JGR, 2021) and are consistent with similar alignments obtained in numerical simulations of the impact of iron-rich projectiles producing a large-scale lunar basin (Wieczorek et al., Science, 2012). |
