Computer Science
Scientific paper
Jan 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000neas.work...12f&link_type=abstract
Near-Earth Asteroid Sample Return Workshop, p. 12
Computer Science
Asteroids, Carbon, Hydrogen, Nitrogen, Oxygen, Isotopes, Meteorites, Gas Analysis, Magnetic Spectroscopy, Asteroid Missions
Scientific paper
The light elements, traditionally H, C, N, and O, are key elements in solar system processes, being the four most abundant reactive elements as well as forming the building blocks of life on Earth. Measurement of their isotopic composition in extraterrestrial materials has been a major component in our efforts to understand the origin and evolution of the solar nebula and the planetary bodies which it formed. In the rare, primitive chondritic meteorites all four of these elements reveal extreme variations in their isotopic composition, characteristic of specific nucleosynthetic processes, in small grains formed in circumstellar environments and which survived homogenization in the solar nebula. However, most material was relatively well homogenized in the solar nebula and any surviving isotopic extremes were further smoothed out during planetary processes such as melting and metamorphism such that typical evolved planetary materials display far more restricted isotopic variation. In the case of hydrogen the observed variations still remain relatively large due to the large mass difference in its two isotopes such that fractionation results in large isotopic shifts. Equally, the isotopic composition of nitrogen remains highly enigmatic with large variations from a range of meteorites and lunar materials. In contrast carbon, and especially oxygen, display very restricted isotopic variations, of the order of one and three percent respectively, in all meteorite types. One of the main compromises made for remote analyses during spaceflight experiments is that of analytical precision. This is particularly true for light element isotopic analyses--to obtain the necessary high precision magnetic sector mass spectrometers have to be used and to extract the species of interest requires heating the samples to high temperature followed by considerable processing of the gases evolved before analysis can commence. This requires mass and power budgets which have so far been entirely unrealistic, although there are on-going projects at the PSRI to improve the precision of instrumentation for remote stable isotope measurements. It is for these reasons that detailed analysis of carbon and oxygen of samples of asteroidal material require analyses to be performed in the laboratory with returned samples. Additional information is contained in the original extended abstract.
Baker Linda
Franchi Ian A.
Pillinger Colin T.
Wright Ian P.
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