Internal structure of the Moon

See also: Geology of the Moon
Moon's internal structure
Olivine basalt collected by Apollo 15.
Thermal state of the Moon at age 100 Ma.[1]

Having a mean density of 3,346.4 kg/m3,[2] the Moon is a differentiated body, being composed of a geochemically distinct crust, mantle, and planetary core. This structure is believed to have resulted from the fractional crystallization of a magma ocean shortly after its formation about 4.5 billion years ago. The energy required to melt the outer portion of the Moon is commonly attributed to a giant impact event that is postulated to have formed the Earth-Moon system, and the subsequent reaccretion of material in Earth orbit. Crystallization of this magma ocean would have given rise to a mafic mantle and a plagioclase-rich crust.

Geochemical mapping from orbit implies that the crust of the Moon is largely anorthositic in composition,[3] consistent with the magma ocean hypothesis. In terms of elements, the lunar crust is composed primarily of oxygen, silicon, magnesium, iron, calcium, and aluminium, but important minor and trace elements such as titanium, uranium, thorium, potassium, sulphur, manganese, chromium[4] and hydrogen are present as well. Based on geophysical techniques, the crust is estimated to be on average about 50 km thick.[5]

Partial melting within the mantle of the Moon gave rise to the eruption of mare basalts on the lunar surface. Analyses of these basalts indicate that the mantle is composed predominantly of the minerals olivine, orthopyroxene and clinopyroxene, and that the lunar mantle is more iron-rich than that of the Earth. Some lunar basalts contain high abundances of titanium (present in the mineral ilmenite), suggesting that the mantle is highly heterogeneous in composition. Moonquakes have been found to occur deep within the mantle of the Moon about 1,000 km below the surface. These occur with monthly periodicities and are related to tidal stresses caused by the eccentric orbit of the Moon about the Earth. A few shallow moonquakes with hypocenters located about 100 km below the surface have also been detected, but these occur more infrequently and appear to be unrelated to the lunar tides.[5]

  1. ^ Maurice, M.; Tosi, N.; Schwinger, S.; Breuer, D.; Kleine, T. (1 July 2020). "A long-lived magma ocean on a young Moon". Science Advances. 6 (28): eaba8949. Bibcode:2020SciA....6.8949M. doi:10.1126/sciadv.aba8949. ISSN 2375-2548. PMC 7351470. PMID 32695879. Text and images are available under a Creative Commons Attribution 4.0 International License.
  2. ^ Making it the second densest satellite in the Solar System after Io
  3. ^ P. Lucey and 12 coauthors, P. (2006). "Understanding the lunar surface and space-Moon interactions". Reviews in Mineralogy and Geochemistry. 60 (1): 83–219. Bibcode:2006RvMG...60...83L. doi:10.2138/rmg.2006.60.2.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  4. ^ "What Chandrayaan 3 has found on moon so far: Oxygen, sulphur, iron, silicon". Hindustan Times. 2023-08-30. Retrieved 2023-11-15.
  5. ^ a b Mark Wieczorek and 15 coauthors, M. A. (2006). "The constitution and structure of the lunar interior" (PDF). Reviews in Mineralogy and Geochemistry. 60 (1): 221–364. Bibcode:2006RvMG...60..221W. doi:10.2138/rmg.2006.60.3. Archived from the original (PDF) on 2014-12-21.{{cite journal}}: CS1 maint: numeric names: authors list (link)