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Science 12 October 2001:
Vol. 294. no. 5541, p. 261
DOI: 10.1126/science.294.5541.261b
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This Week in Science
The surface of the Moon, brought back by the Apollo missions, is a useful tracer of solar system processes as divergent as solar convection and the formation of the Moon. Nishiizumi and Caffee (p. 352) have quantified a beryllium-10 excess in Apollo-17 lunar soils that they attribute to low-energy solar wind ions rather than to higher energy galactic or solar cosmic rays. The inferred flux rate indicates that beryllium-10 is directly ejected in the solar wind without any mixing in the deeper convective zones of the Sun. The Moon probably formed in a giant impact between the proto-Earth and a Mars-sized bolide that hit the Earth. Analysis of the oxygen isotopic concentrations of Apollo lunar soils by Wiechert et al. (p. 345) indicate that the oxygen isotopes are homogeneous and similar to terrestrial measurements. Thus, the proto-Earth and the smaller, hypothetical bolide were likely composed of similar materials formed at about the same distance from the Sun.
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Science. ISSN 0036-8075 (print), 1095-9203 (online)
