Lunar magma ocean

A simplified animation of the Lunar Magma Ocean crystallization sequence
Animation showing the cross-section of the LMO as it crystallizes over time. The first solids to form (e.g., olivine) are denser than the surrounding magma, thus sink towards the interior. After about 80% of the LMO has crystallized, less dense solids (i.e., plagioclase) begin to form and float towards the surface, forming the primordial crust of the Moon.

The Lunar Magma Ocean (LMO) is the layer of molten rock that is theorized to have been present on the surface of the Moon. The LMO was likely present on the Moon from the time of the Moon's formation (about 4.5 or 4.4 billion years ago[1]) to tens or hundreds of millions of years after that time. The LMO was a thermodynamic consequence of the Moon's relatively rapid formation in the aftermath of a giant impact between the proto-Earth and another planetary body. As the Moon accreted from the debris from the giant impact, gravitational potential energy was converted to thermal energy. Due to the rapid accretion of the Moon (in about a month to a year),[2][3][4] thermal energy was trapped since it did not have sufficient time to thermally radiate away energy through the lunar surface. The subsequent thermochemical evolution of the LMO explains the Moon's largely anorthositic crust, europium anomaly, and KREEP material.

The LMO was initially proposed by two groups in 1970 after they analyzed anorthositic rock fragments found in the Apollo 11 sample collection.[5][6] Wood et al. used fragments of bulk sample 10085 for their analyses.[7] Ferroan anorthosite (FAN) rocks found during the Apollo program are composed primarily (over 90%) of the mineral plagioclase.[8] More specifically, FAN rocks found on the Moon consist of the calcium (Ca) end-member of plagioclase (i.e., anorthite).[9] This suggests that at least upper layers of the Moon were molten in the past due to the purity of lunar anorthosites and the fact that anorthite generally has a high crystallization temperature.[10]

Lunar ferroan anorthosite rock from Apollo 16
Lunar FAN rock from Apollo 16 (Sample 60025).
  1. ^ Touboul, Mathieu; Kleine, Thorsten; Bourdon, Bernard; Palme, Herbert; Wieler, Rainer (February 2009). "Tungsten isotopes in ferroan anorthosites: Implications for the age of the Moon and lifetime of its magma ocean". Icarus. 199 (2): 245–249. Bibcode:2009Icar..199..245T. doi:10.1016/j.icarus.2008.11.018. ISSN 0019-1035.
  2. ^ Ida, Shigeru; Canup, Robin M.; Stewart, Glen R. (September 1997). "Lunar accretion from an impact-generated disk". Nature. 389 (6649): 353–357. Bibcode:1997Natur.389..353I. doi:10.1038/38669. ISSN 0028-0836. S2CID 19073356.
  3. ^ Kokubo, E (December 2000). "Evolution of a Circumterrestrial Disk and Formation of a Single Moon". Icarus. 148 (2): 419–436. Bibcode:2000Icar..148..419K. doi:10.1006/icar.2000.6496.
  4. ^ Takeda, Takaaki; Ida, Shigeru (2001-10-10). "Angular Momentum Transfer in a Protolunar Disk". The Astrophysical Journal. 560 (1): 514–533. arXiv:astro-ph/0108133. Bibcode:2001ApJ...560..514T. doi:10.1086/322406. ISSN 0004-637X. S2CID 119060440.
  5. ^ Smith, J. V.; Anderson, A. T.; Newton, R. C.; Olsen, E. J.; Wyllie, P. J. (July 1970). "A Petrologic Model for the Moon Based on Petrogenesis, Experimental Petrology, and Physical Properties". The Journal of Geology. 78 (4): 381–405. Bibcode:1970JG.....78..381S. doi:10.1086/627537. ISSN 0022-1376. S2CID 129018519.
  6. ^ Wood, J. A.; Dickey, J. S.; Marvin, U. B.; Powell, B. N. (1970-01-30). "Lunar Anorthosites". Science. 167 (3918): 602–604. Bibcode:1970Sci...167..602W. doi:10.1126/science.167.3918.602. ISSN 0036-8075. PMID 17781512. S2CID 20153077.
  7. ^ "Apollo Sample Description". curator.jsc.nasa.gov. Retrieved 2019-09-29.
  8. ^ "PSRD: The Oldest Moon Rocks". www.psrd.hawaii.edu. Retrieved 2019-09-27.
  9. ^ Dowty, Eric; Prinz, Martin; Keil, Klaus (November 1974). "Ferroan anorthosite: A widespread and distinctive lunar rock type". Earth and Planetary Science Letters. 24 (1): 15–25. Bibcode:1974E&PSL..24...15D. doi:10.1016/0012-821x(74)90003-x. ISSN 0012-821X.
  10. ^ Reynolds, Stephen J. (2015-01-12). Exploring geology. Shaw, Cynthia C. (Fourth ed.). New York, NY. p. 123. ISBN 9780078022920. OCLC 892304874.{{cite book}}: CS1 maint: location missing publisher (link)