Absence of a long-lived lunar dynamo: opportunities to learn about the early Earth and solar wind during future exploration
Abstract
Recent single crystal paleointensity (SCP) data from Apollo samples reveal null magnetic fields for the Moon between 3.9 and 3.2 Ga (Tarduno et al., 2021). The absence of a long-lived lunar magnetic field resolves the multiple paradoxes associated with prior (Cisowski et al., 1983) and continuing (Evans and Tikoo, 2021) interpretations of a core dynamo. These paradoxes include the lack of pervasive large-scale lunar magnetic anomalies, and the lack of sufficient core energy to sustain a dynamo needed to explain nominal high magnetic field measurements from prior studies of bulk Apollo samples, if such data actually recorded a global lunar magnetic field. Measurements of young lunar glass indicate that the strong nominal field reported in prior studies might instead record impact-induced magnetizations associated with charge separation (Tarduno et al., 2021). Here we report new SCP and whole rock paleointensity data from ~3.75 billion-year-old high-Ti mare basalt samples 70035 and 75035. Bulk rock mare basalts are known to contain large non-ideal magnetic minerals (multidomain state, MD). In contrast, our new SEM analyses show that the single crystals analyzed (feldspars) contain minute magnetic minerals in the size range of ideal magnetic recorders (single domain). Moreover, we find that the single crystals record null remanent fields, whereas the bulk rocks nominally record anomalously high (>100 μT) fields. We attribute the latter to mark the preference of MD grains to preserve impact-induced magnetizations, whereas the SD-bearing single silicates document the true absence of a long-lived magnetic field of the Moon. As the Moon was not shielded by a magnetosphere for most of its history, solar winds are expected to have implanted helium, hydrogen, and other volatile resources into the regolith. Lunar soils buried and sealed by later lava flows (Fagents et al., 2010) should be considered prime scientific targets for future missions. The isotopic signatures of buried soils can preserve records of the composition of ancient solar winds and Earth's atmosphere that are essential for understanding the terrestrial environment during the earliest development of life on the planet.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.P46A..05Z