Studying solar wind

An international team of scientists, including Dr Chris Coath from the University of Bristol, have measured oxygen isotopes in solar wind, captured by NASA's Genesis mission, to infer the isotopic composition of the Sun, and, by inference, the solar system as a whole. Their results are published in Science.

NASA's Genesis mission crash-landed back on Earth in 2004. The spacecraft spent more than two years in orbit around the sun collecting solar wind, which consists of charged particles, on various ultra-pure collector materials.

Fortunately, the collector with the greatest scientific value survived the crash almost intact. Its primary purpose was to measure the relative abundances of the three isotopes of oxygen: 16O, 17O and 18O.

Despite the length of the mission, the solar wind is so rarefied that the small number of atoms collected required a dedicated mass spectrometer, the MegaSIMS, and years of technique development to measure the tiny quantities of implanted oxygen with sufficient precision. Dr Coath designed the ion-optics of this unique instrument.

Oxygen isotopes have long posed a puzzle for scientists studying their distribution in the solar system. Inclusions in meteorites called CAIs, which are the earliest solids to have condensed in the solar system, and other refractory minerals in primitive meteorites, are found to be depleted (relative to the Earth) in the heaviest, and least abundant isotopes, 17O and 18O.

One important question, which could not be answered by meteorite or even planetary studies, is what is the average oxygen isotope composition of the solar system as a whole? Knowing this would put constraints on the mechanisms which could have given rise to the observed distribution.