A Comparison of Oxidized Carbon Abundances among Comets

Details A Comparison of Oxidized Carbon Abundances among Comets A Comparison of Oxidized Carbon Abundances among Comets

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.4803d&link_type=abstract

American Astronomical Society, DPS meeting #39, #48.03; Bulletin of the American Astronomical Society, Vol. 39, p.507

Astronomy and Astrophysics

Astronomy

1

Scientific paper

Comets contain relatively primitive icy material remaining from the epoch of Solar System formation, however the extent to which they are modified from their initial state is a fundamental question in cometary science. One means of assessing the degree to which ices were processed prior to their incorporation into the nucleus is to measure the relative abundances of chemically related parent volatiles. For example, formation of C2H6 by hydrogen atom addition reactions (e.g., to C2H2) on surfaces of icy-mantled grains prior to their incorporation into the nucleus was proposed to explain the high C2H6 to CH4 abundance observed first in C/1996 B2 (Hyakutake)1 and then in subsequent comets. Comparing the abundance ratio C2H6/C2H2 among comets can provide information on the efficiency of this process.
CO should also be hydrogenated on grain surfaces. Laboratory irradiation experiments on interstellar ice analogs have shown this process to be efficient only at very low temperatures, the resulting yields of H2CO and CH3OH being highly dependent both on hydrogen density (i.e., fluence) and on temperature in the range 10-25 K.2,3 Here, we compare the oxidation sequence of carbon in comets observed with NIRSPEC at Keck-2 and CSHELL at the NASA-IRTF. Their compositions are used to assess the efficiency of H-atom addition. Possible implications regarding formation conditions will be discussed.
This work is supported by the NASA Astrobiology Program under RTOP 344-53-51, and by the NASA Planetary Astronomy Program under RTOPs 344-32-30-07 and 344-32-98.
References: 1Mumma et al. 1996 Science 272:1310 2Hiraoka et al. 2002 Astrophys. J. 577:265 3Watanabe et al. 2004 Astrophys. J. 616:638

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