Planetary geologists have measured different abundances of oxygen isotopes in samples from the Earth, the Moon, Mars, and meteorites, but were long unable to obtain reference values for the isotope ratios in the Sun, believed to be the same as those of the primordial solar nebula. Analysis of a silicon wafer exposed to the solar wind in space and returned by the crashed Genesis spacecraft has shown that the Sun has a higher proportion of oxygen-16 than does the Earth. The measurement implies that an unknown process depleted oxygen-16 from the Sun's disk of protoplanetary material prior to the coalescence of dust grains that formed the Earth.
What celestial object eluded efforts to measure oxygen? What molecule does the Sun have in higher proportion than Earth? What spacecraft contained data to determine the oxygen content of the Sun? What type of process was involved the the depletion of the Sun's oxygen 16? Before the formation of which planet, did Sol lose oxygen 16?