MIT OpenCourseWarehttp://ocw.mit.edu 12.002 Physics and Chemistry of the Earth and Terrestrial Planets Fall 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.The Moon Before the Apollo missions, Urey proposed Moon was undifferentiated object-never melted since formation Now we know that it is composed of two terranes: 1. Highlands (mostly highlands) - rough high topography, bright, heavily cratered (84% of surface) 2. Mare - low, dark, lightly cratered (16% of surface) 1966 gamma ray spectroscopy from Soviet Luna 10 orbiter: Measured 40K, 235U, and 232Th and found them to be chondritic or subchondritic over highlands (like mantle) and superchondritic over mare. Conclusion: Lunar mare are basaltic but lunar highlands are not granitic like Earth’s continents. 1968 US Surveyor landers. First in situ analyses of mare and highlands sites. 1969 - 1972 six Apollo manned missions – 380 kg of rock and soil Mare composed of basalt (pyroxene, olivine, plagioclase). Ages 3.9 - 3.2 Ga (mare volcanism persisted to 1 Ga). Meteorites, young mare basalts - Urey is wrong: Moon is differentiated Highlands have two plagioclase-rich compositional types: -Anorthosite (>98% anorthite CaAl2Si2O8 which is Ca-rich, Na-K poor plagioclase) -Mg-suite (plagioclase and pyroxene and olivine) All the rocks are extremely dry! Major element composition of the bulk Moon is grossly similar to Earth's mantle Uncompressed density 4050 kg m-3 for Earth versus 3300 kg m-3 for Moon Differences between Earth and Moon: Moon enriched in FeO, depleted in Fe metal Moon depleted in siderophile elements (iron-loving) Moon depleted in volatile and moderately volatile elements (Na,K) Moon enriched in refractory elements (Ca, Al,
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