SOLAR WIND NITROGEN IN GENESIS GOLD-ON-SAPPHIRE (AuOS) COLLECTORS

Introduction: Nearly four decades of experimental studies have failed to agree on an isotopic composition for solar wind (SW) nitrogen implanted in lunar regolith grains. Estimates of ! 15 N range from > +200 ‰ [1] to < -250 ‰ [2]. Its actual value is crucial, not only for untangling component mixtures in the lunar system but also in elucidating the sources and isotopic evolution of N in other solar system objects, where ! 15 N spans >1000 ‰. Determining N composition in the contemporary SW was thus a high priority objective of the Genesis mission. Here we report measurements of SW! 15 N in N extracted from Genesis AuOS collectors. Technique: N and light noble gases were released from the AuOS gold film by amalgamation at ~30oC. Fig. 1 illustrates the process. The Hg-Au amalgam is liquid; subsequent removal of Hg vapor by cryopumping at -80oC results in the deposition of tiny spheres and rivulets of recondensed gold on the sapphire substrate (visible in Fig. 1B at higher magnification). Blanks and Extraction Efficiency: A great advantage of low-T amalgamation is that it does not release N contaminants which are mobilized by high-T extraction techniques. AuOS blanks for N are consequently lower by factors of thousands (Fig. 2). That this is not due to inefficient N2 extraction is shown in Fig. 2 by