Apollo 11 and 12 solar wind composition experiments: Fluxes of He and Ne isotopes

During the Apollo 11 and 12 landings, solar wind ions were collected in a metal foil for periods of 77 min and 18 hours 42 min, respectively. Mass spectrometric analyses of the collected solar wind particles were made in the laboratory and give the following fluxes and relative abundances for the Apollo 11 and 12 exposure periods, respectively: 4He flux: (6.2±1.2)×106 and (8.1±1.0)×106 cm−2 sec−1; 4He/³He: 1860±140 and 2450±100; 4He/20Ne: 430±90 and 620±70; 20Ne/22Ne:13.5±1.0 and 13.1±0.6; 22Ne/21Ne: —— and 26±12. The differences in the 4He/³He and 4He/20Ne ratios are significant and are interpreted as time variations in the composition of the interplanetary plasma. From He/O ratios reported in the literature, an approximate solar wind O/Ne ratio of 10 is derived. Comparisons of the results of the solar wind composition experiment with data from implanted solar wind particles in lunar soil and with trapped gases in aubritic meteorites indicate a secular variation in the 4He/³He ratio at the solar surface.