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

Abstract- 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 et al. (2010, 2011); nitrogen in the solar wind is depleted in ¹⁵N relative to nitrogen in the Earth's atmosphere. Specifically, our array data yield values for ¹⁵N/ ¹⁴N of (2.17±0.37)×10 ^-3 and (2.12±0.34)×10 ^-3, depending on data-reduction technique. This result contradicts preliminary results reported for previous measurements on B/C array materials by Pepin et al. (2009), so the discrepancy between Marty et al. (2010, 2011) and Pepin et al. (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)×10 ¹²cm ^-2. This value is higher than that derived by backside profiling of a Genesis silicon collector (Heber et al. 2011a).