[Previous] | [Session 56] | [Next]
P. A. Gerakines, K. Harman, E. Saperstein, K. M. Arnoult, T. J. Wdowiak (Astro- and Solar-System Physics Program, Dept. of Physics, Univ. of Alabama at Birmingham)
Most lines of sight that intersect material in the interstellar medium (ISM) contain a complex infrared (IR) absorption signature near 3.4 microns, representative of some linear combination of aromatic and aliphatic carbon compounds. Emission signatures are found in the shells surrounding post-AGB stars, in the emission of comets, and in the absorption spectra of insoluble extracts from meteorites. These and other spectral signatures of the ISM have been previously reproduced (by Arnoult et al. 2000 and references therein) in a laboratory plasma product derived from a naphthalene precursor, including features having peak wavelengths coincident with those of the unidentified IR emission bands and the bump at 217.5nm in the interstellar UV extinction curve. This laboratory-derived material is a representative analog of carbonaceous materials formed in the atmospheres of stars and those found throughout the ISM. The agreement in the IR spectra of the plasma product and the meteoritic extracts implies an evolution whereby this material, formed in the atmospheres of stars, is included into new planetary systems. In order to complete this connection, the carbonaceous material must first become part of a dense interstellar cloud, where cold dust grains are known to form icy mantles of condensed volatiles and are photolyzed by UV light from young protostars. In this work, we have coated our plasma product material with ices representative of interstellar icy grain mantles and subjected them to UV photolysis in the laboratory. Such a scenario is a realistic approach to the actual circumstances in the dense ISM and provides clues to the origin of organic molecules that became incorporated into the planetesimals of the early Solar System and ultimately supplied the molecular resources for life on Earth and probably elsewhere.
Reference: Arnoult, K. M., T. J. Wdowiak, and L. W. Beegle, ApJ 535, 815-822 (2000).