The isotopic composition and fluence of solar-wind nitrogen in a genesis B/C array collector

We have measured the isotopic composition and fluence of solar-wind nitrogen in a diamond-like-carbon collector from the Genesis B/C array. The B and C collector arrays on the Genesis spacecraft passively collected bulk solar wind for the entire collection period, and there is no need to correct data for instrumental fractionation during collection, unlike data from the Genesis Concentrator. This work validates isotopic measurements from the concentrator by Marty etal. (2010, 2011); nitrogen in the solar wind is depleted in 15N relative to nitrogen in the Earths atmosphere. Specifically, our array data yield values for 15N/14N of (2.17 +/- 0.37) x 10-3 and (2.12 +/- 0.34) x 10-3, depending on data-reduction technique. This result contradicts preliminary results reported for previous measurements on B/C array materials by Pepin etal. (2009), so the discrepancy between Marty etal. (2010, 2011) and Pepin etal. (2009) was not due to fractionation of solar wind by the concentrator. Our measured value of 15N/14N in the solar wind shows that the Sun, and by extension the solar nebula, lie at the low-15N/14N end of the range of nitrogen isotopic compositions observed in the solar system. A global process (or combination of processes) must have operated in interstellar space and/or during the earliest stages of solar system formation to increase the 15N/14N ratio of the solar system solids. We also report a preliminary Genesis solar-wind nitrogen fluence of (2.57 +/- 0.42) x 1012 cm-2. This value is higher than that derived by backside profiling of a Genesis silicon collector (Heber etal. 2011a).