Review

Analysis of lunar samples: Implications for planet formation and evolution

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Science  19 Jul 2019:
Vol. 365, Issue 6450, pp. 240-243
DOI: 10.1126/science.aaw7580

Figures

  • Fig. 1 Diagram of the lunar magma ocean model.

    Convection (arrows) within the magma ocean circulates the magma. Crystallization of dense olivine and pyroxene (green) and buoyant plagioclase (gray) separates the magnesium-rich minerals of the interior from the anorthositic crust. The thickness of the lunar crust is exaggerated by about a factor of 10 for display.

  • Fig. 2 Map of the distribution of thorium (Th) on the lunar surface.

    Data from the Lunar Prospector and Clementine missions (82) allow division of the lunar crust into three compositionally distinct terranes, outlined here in white. On the near side is the Th-rich Procellarum-KREEP Terrane (PKT); the far side is dominated by the Th-poor Feldspathic Highlands Terrane (top) penetrated by the impact that formed the South Pole–Aitken basin (bottom) that exposed slightly more Th-rich material, but nowhere near as Th-rich as in the PKT. [Figure provided by Bradley Jolliff updated and modified from the figure shown in (12)]

  • Fig. 3 Illustration of a common source history for lunar igneous rocks.

    The neutron fluence–corrected 142Nd/144Nd (μ142Nd is the deviation in the sample’s 142Nd/144Nd relative to the laboratory standard in parts per million) is plotted against the 147Sm/144Nd ratio of the sample (highlands rocks) or calculated for the source of the basalts according to their initial 143Nd/144Nd ratio. Both Nd isotope ratios are modified by the radioactive decay of 146Sm (half-life 103 million years) to 142Nd and that of 147Sm (half-life 106 billion years) to 143Nd. The lines on the diagram show the slopes expected for different ages (Byr, billion years) for the process that created the range in Sm/Nd ratios that resulted in the initial isotopic range in these rocks. The alignment of the data for mare basalts, KREEP-rich rocks, and various highland samples along a single line of slope corresponding to an age of 4.38 billion years indicates that the source materials of these lavas formed during a single short-duration event. [Data from (27, 29, 83, 84)]

  • Fig. 4 Impact rate on the lunar crust through time.

    Calibration points are based on crater densities from different age terranes sampled at the Apollo (designated by A) and Luna 16 landing sites. The gray peak at 3.9 billion years represents the hypothesized spike in impacts associated with the late heavy bombardment. [Figure adapted from (85)]

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