Other
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.459d&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 459-460
Other
Astronomical Models, Interstellar Matter, Meteoritic Composition, Meteoritic Microstructures, Moisture Content, Deuterium, Ion Probes, Ionization, Ratios
Scientific paper
The D/H ratio of three meteorites (Renazzo CR, Abee E3, and Semarkona LL3) were measured with the CRPG Nancy ion microprobe. These meteorites are well known for their large D enrichments found in the organic macromolecules. The observed in-situ variations of the D/H ratio cover the range of 7 x 10-5 to 8 x 10-4. Other secondary ions were measured together with H and D to characterize the H carriers. The high D/H ratios measured in water-bearing minerals in Semarkona and in Renazzo could not have been reached thermally within a dense solar nebula. Ion or radical reactions are the only known chemical pathways to yield such a D enrichment. Until now, among D-rich meteoritic compounds, only organic macromolecules have been identified in the interstellar medium. Our new data suggest that interstellar water should also be enriched in D and water condensed in an interstellar environment has been preserved during the formation of solar system solids. It is possible to model such an environment by reactions such as: D + H30(+) reversable reaction H2DO(+) + H and H3O(+) + e yields H2O + H. Using the usual astrophysical approximations reaction rate calculations show that, for a fractional ionization lying between 10-5 and 10-6, the meteoritic phyllosilicate D/H ratio can be reached at temperatures between 120 and 80 K. These results show that synthesis of water was confined in the low-pressure outer regions of the nebula where ions or radicals can be produced by UV molecular dissociation. According to these presently calculated condensation temperatures, it seems impossible to admit that solar system water was a by-product of a condensation sequence in the solar nebula.
Deloule Etienne
Robert Frédéric
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