The oxygen isotopic composition of the Sun: implications for solar nebula chemistry

We have measured the oxygen isotopic composition of the solar wind, captured and returned to Earth by NASA's Genesis mission. The data demonstrate that the Earth, Moon, Mars, and bulk meteorites are depleted in 16O by ~7% relative to the bulk solar system in a non-mass-dependent manner. Gas phase photochemistry, occurring either in the solar nebula or in its progenitor molecular cloud, is most likely responsible for changing the isotopic composition of planetary materials in the inner solar system prior to planetesimal accretion. Understanding how, when, and where the rocky planets acquired an isotopic composition distinct from the average composition of the dust and gas from which the solar system formed is a major challenge for the science of planetary origins.