From Interstellar Dust via Comets to Life?
Abstract
More than 120 interstellar and circumstellar molecules are currently identified in the gas phase along with a small fraction of interstellar dust composed of amixture of materials from various cosmic sources (Spaans & Ehrenfreund 1999). Recent ground-based observations and satellite data from the Infrared Space Observatory ISO have provided revolutionary results concerning the nature of cosmic 'dust particles. Interstellar grains act as an important catalyst in the interstellar medium. Processes such as ultraviolet irradiation, cosmic ray bombardment mid - temperature variations determine the grain mantle growth and chemical evolution.
The incorporation of interstellar matter in meteorites and comets in the pre-solar nebula provides the basis for the "cosmic dust connection" (Ehrenfreund 1999). A comparison of interstellar and cometary dust using recent ISO data and ground-based measurements has revealed important similarities but also indicated that comets contain beside pristine interstellar material, admixtures of processed material (Ehrenfreund et al. 1997, Ehrenfreund 2000). The investigation of molecules in interstellar clouds and comets is essential to reveal the link between dust in the interstellar medium and in the Solar System and provides important clues on the prebiotic chemical evolution on Earth. In space most of the chemical evolution toward complex molecules takes place in the solid phase, particularly accessible to laboratory simulations. We present laboratory data relevant to ultraviolet irradiation, cosmic ray bombardment and thermal processing of dust. This allows to reconstruct the conditions in.the.protostellar environment and to monitor the evolution of simple carbon bearing species to complex molecules and aromatic networks. New results indicate in fact a lack of radiation processing in dense clouds, which may strongly decrease the yield of organics formed in those environments (Ehrenfreund et al. 1998). We present studies on the outgassing properties of bright comets (such as Hale-Bopp and Hyakutake) which are compared to recent interstellar dust model predictions. We critically discuss whether interstellar molecules brought by comets may act as precursors for biogenic molecules.- Publication:
-
Origins of Life and Evolution of the Biosphere
- Pub Date:
- August 2000
- DOI:
- 10.1023/A:1017300204711 %K
- Bibcode:
- 2000OLEB...30..342E