Analysis of Carbon and Nitrogen in Three Particles from Comet Wild-2

Details Analysis of Carbon and Nitrogen in Three Particles from Comet Wild-2 Analysis of Carbon and Nitrogen in Three Particles from Comet Wild-2

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p51e1239g&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P51E-1239

Physics

6008 Composition (1060), 6015 Dust, 6023 Comets: Dust Tails And Trails (6210), 6040 Origin And Evolution, 6210 Comets (6023)

Scientific paper

Cometary carbon and nitrogen are of interest because 1) they are the principal components of the `organic' phase(s) found in all comets, 2) they may be a useful indicators of redox conditions in the regions where comets formed and 3) they may have influenced the Earth`s atmospheric composition, surface temperatures (through the greenhouse effect), and even the evolution of life. We measured the total numbers of C, N, O, and Si atoms in three particles from comet Wild-2, C23, C447, and C21 by using a non-destructive nuclear reaction method (NRA). Three particles were selected for study based on their color (dark) and size ( >5 μm) and pressed into 99.999% indium foils. For NRA, a 1.9-MeV deuteron beam induces nuclear reactions on 12C, 14N, 16O and ^{28}Si resulting in energetic proton emission. Additional analyses of selected elements were made by scanning electron microscopy (SEM) and by synchrotron x-ray fluorescence. Particles C23 and C447 consist mainly of silica, likely from aerogel. The C/N ratio of C23, resembles that of CM chondrites, Halley dust, and the acid-insoluble residue from carbonaceous chondrites thought to be primitive. The lower C/N ratio of C447, is closer to that of CI chondrites, mixed Halley dust and ice, and some interplanetary dust particles. Carbon dominates the elemental composition of particle C21. Its higher C/N ratio is closer to those of CO and CV chondrites. The SEM results show several elements not seen in the nuclear reaction analysis, namely Na, Al, Mg, and Ca. In carbonaceous extraterrestrial materials the C/N atom-atom ratios decrease with increasing primitiveness, from values greater than 50 in CO and CV chondrites, to ~10 in CI chondrites and Halley dust and ice, to 0.6 measured remotely at Comet Wild-2. The C/N ratios of our 3 particles span most of the meteoritic range. Textural evidence shows that deceleration in aerogel heated the Wild-2 (Stardust) particles and altered them. We infer from these comparisons that an appreciable fraction of the cometary nitrogen occurs in more volatile compounds that move or dissipate during aerogel capture.

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