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Investigating the influence of an unmagnetized versus magnetized Earth on the relative solar wind and Earth atmosphere contributions to lunar soil

Presentation #215.04 in the session Planetary Space Physics Talks (Oral Presentation)

Published onOct 23, 2023
Investigating the influence of an unmagnetized versus magnetized Earth on the relative solar wind and Earth atmosphere contributions to lunar soil

Observations of lunar regolith composition have revealed the need for a source that differs in the abundance of light volatile elements (like H, He, C, N, and some noble gases) from the solar wind. Mass supply from Earth’s atmosphere has been previously proposed as one possibility if the Earth incurred phases of vanishing geomagnetic field on geological time scales that might increase the ratio of Earth’s atmosphere mass flux to solar wind flux that the Moon encounters [Ozima et al., 2005]. Here we develop a framework for studying the relative escape from unmagnetized and magnetized evolution of a planetary atmosphere subject to the impinging stellar wind that combines 3-D MHD numerical simulations using the adaptive mesh refinement (AMR) multi-physics code, AstroBEAR*, with theoretical analyses. We specifically determine the orbit-averaged Earth wind mass flux at the lunar surface for a range of plausible solar wind conditions to which the current geo-magnetosphere and paleoatmosphere (induced magnetosphere) may have been subject. Using this, we quantify both the role the intrinsic geomagnetic field plays on the total escaping Earth’s atmosphere flux encountered by the Moon and the relative fraction of upper versus lower atmosphere flux transported. We find that neither effect considerably changes the relative abundances of solar wind and Earth atmosphere flux to the lunar surface. The Earth’s atmosphere flux remains small in both cases because the Moon spends only a small fraction of its orbit within a cross-section that provides direct access to Earth’s atmosphere material. Our model does not track specific chemical species and their energy states, primary factors controlling implantation into the regolith, and makes predictions only for the relative wind and atmospheric flux aggregate compositions rather than any particular element. We do not address the influence of the magnetic field in determining the composition distribution of specific elements from Earth that arrive at the Moon. Similarly, our atmospheric model does not include detailed transport processes for individual ions.

* http://astrobear.pas.rochester.edu/

References

Ozima, M., Seki, K., Terada, N. et al. Terrestrial nitrogen and noble gases in lunar soils. Nature 436, 655–659 (2005). https://doi.org/10.1038/nature03929

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