Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.2112h&link_type=abstract
American Astronomical Society, DPS meeting #42, #21.12; Bulletin of the American Astronomical Society, Vol. 42, p.987
Astronomy and Astrophysics
Astronomy
Scientific paper
Water is perhaps the most important molecule in the solar system, and understanding the origin and distribution of water in planetary interiors has important ramifications for understanding the evolution of planetary bodies. Here we report the first in-situ measurements of the isotopic composition of hydrogen dissolved in volcanic glass samples recovered from the Moon by the Apollo 15 mission. We examined specific groups of lunar glasses contained in three samples recovered by the Apollo 15 mission (15426,32; 15426,138 and 15427) with eruption ages of 3.35 to 3.65 Ga; H2O and D/H ratios were measured by SIMS. Yellow-brown volcanic glasses contain the highest concentrations of H2O (up to 70 ppm) which is two times higher than our previous measurements, while green glasses contain smaller amounts of water (4 - 17 ppm H2O). After correction for cosmogenic contributions, our data exhibit a systematic negative correlation of δD (-200‰ to +2500‰) with water content. The systematic nature of the data correlation, and the heterogeneous H2O concentrations and D/H data, indicate that hydrogen isotopes were fractionated in these lunar magmas during kinetic degassing during eruption. The average δD of the five highest-H2O glasses is +340‰ (+180‰/-240‰) this δD range overlaps the range of carbonaceous chondrites and terrestrial water. Furthermore, it is very likely that the original pre-eruptive δD value of these lunar magmas was significantly lower, and that kinetic D/H fractionation has resulted in preferential loss of H during magmatic degassing. As a result, within the uncertainties in our measurements and correction for the effects of cosmic ray spallation and degassing, we conclude that juvenile magmatic water in the lunar interior has a D/H ratio that is indistinguishable from terrestrial water. This study is the first to identify a planetary body with a hydrogen isotope composition that is the same as the Earth.
Hauri Erik
Rutherford Malcolm C.
Saal Alberto E.
van Orman James A.
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