Long‐term observations and physical processes in the Moon's extended sodium tail
Files
Accepted manuscript
Date
2021-03
Authors
Baumgardner, Jeffrey
Luettgen, Sarah
Schmidt, Carl
Mayyasi, Majd
Smith, Steven
Martinis, Carlos
Wroten, Joei
Moore, Luke
Mendillo, Michael
Version
Accepted manuscript
OA Version
Citation
J. Baumgardner, S. Luettgen, C. Schmidt, M. Mayyasi, S. Smith, C. Martinis, J. Wroten, L. Moore, M. Mendillo. 2021. "Long‐Term Observations and Physical Processes in the Moon's Extended Sodium Tail." Journal of Geophysical Research: Planets, Volume 126, Issue 3, https://doi.org/10.1029/2020je006671
Abstract
The lunar surface is constantly bombarded by the solar wind, photons, and meteoroids, which can liberate Na atoms from the regolith. These atoms are subsequently accelerated by solar photon pressure to form a long comet-like tail opposite the sun. Near new moon, these atoms encounter the Earth's gravity and are “focused” into a beam of enhanced density. This beam appears as the ∼3° diameter Sodium Moon Spot (SMS). Data from the all sky imager at the El Leoncito Observatory have been analyzed for changes in the SMS shape and brightness. New geometry-based relationships have been found that affect the SMS brightness. The SMS is brighter when the Moon is north of the ecliptic at new moon; the SMS is brighter when new moon occurs near perigee; and the SMS peaks in brightness ∼5 h after new moon. After removing these effects, the data were analyzed for long term and seasonal patterns that could be attributed to changes in source mechanisms. No correlation was found between the SMS brightness and the 11-year solar-cycle, the proton or the He++ flow pressure, the density, the speed or the plasma temperature of the solar wind, but an annual pattern was found. A ∼0.83 correlation (Pearson's “r”) was found between the SMS brightness and a 4-year average of sporadic meteor rates at Earth, suggesting a cause-and-effect. The new insights gained from this long-term study put new constraints on the variability of the potential sources of the Na atoms escaping from the Moon.
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This article is protected by copyright. All rights reserved. This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as DOI: 10.1029/2020JE006671.