Evidence of at least two extra-selenial components accreting on the Moon - In search for the oxygen isotopic
composition of the solar component trapped in lunar metallic grains. Ko Hashizume1 and Marc Chaussidon2,
1Dept. of Earth & Space Sciences, Osaka University, Toyonaka, Japan (kohash@ess.sci.osaka-u.ac.jp), 2CRPG-
CNRS, Nancy, France.
The surface of the Moon has been exposed over bil-
lions of years to irradiation by solar ions and to contri-
butions of various extraterrestrial sources. Potential
contributors include interplanetary dust particles and
micrometeorites which dominate the present-day mass
flux of meteoritic matter to the Earth’s surface, meteor-
ites and comets. For example, from studies of nitrogen
isotopes among various lunar soils sampled at different
locations, a competition of at least two fluxes with dif-
ferent origins accreting onto the moon surface was
clearly observed [1]. The proportions of these compo-
nents differed largely among samples, or grain-by-grain
within the same sample. These proportions appear to
differ among different elements, depending on their
relative abundances in the respective fluxes and on
their trapping mechanism into lunar samples. It is im-
portant to note that our current knowledge of the oxy-
gen fluxes reaching the surface of the Moon is very
poor, mainly because of the sparse available data. The
goal of this study is to better determine the proportion
of the different fluxes - potentially, solar, asteroidal
and cometary - recorded among lunar grains in the case
of oxygen, and to decipher the endmember solar iso-
topic composition.
Hashizume & Chaussidon (2005) [2] have previ-
ously reported the presence among metallic grains from
lunar sample 79035 of an oxygen component enriched
in 16O (∆17O ( = δ17O - 0.52 x δ18O ) < -20 ± 4 ‰).
Silicate grains from this sample were enriched in D-
depleted hydrogen (δD < -930 ‰) [3] and solar noble
gases [1], suggesting not only enrichment of the solar
component in this sample, but a relativel