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Cometary grains are commonly considered to be the precursors of organic materials in early life on the Earth. It is a persistent mystery, however, how chemical evolution within the earliest protocells was triggered. We discuss the type of organics measured from Comet p/Wild-2, using the Cometary and Intersellar Dust Analyzer (CIDA). This instrument is not sensitive to mineralic cores of dust particles due to their low-impact velocities (6 km/s). The CIDA data allows us to analyze the organic fraction of interstellar dust at ~1 AU from the Sun. Surprisingly, it mainly consists of quinone-type polycyclics, some of them similar to pyrrolo-Cquinoline-Cquinone. Strong redox catalysts are apparently required to trigger the earliest chemical evolutionary steps. Our understanding of the thermochemical evolution of accretion from interstellar clouds containing cosmic grains to comets qualitatively and quantitatively requires a comprehensive understanding of the production of water and CO from the comets. The"dirty snowball" model is rejected as a suitable model for "fresh" comets. Apparently the primordial source of water is twofold: (1) a signicant fraction of cometary clathrates is contained in the mineralic and the organic fractions, producing water by evaporation; (2) rich oxygen containing PAH's in the organic phase produces water by solar radiation-induced chemical processes. [ABSTRACT FROM AUTHOR]

Comets have intrigued mankind over centuries. The use of improved astronomical equipment revealed an ever-increasing number of features. It took, however, until the advent of in situ measurements by the means of space research until the complexity of cometary physics and chemistry was recognized. Three comets have been visited by spacecrafts up to now, one mission is in progress (Deep Impact to Tempel-1, in July 2005) and one is planned (Rosetta to Churyumov-Gerasimenko, in 2013), 2 missions failed (CRAF was cancelled in 1992, CONTOUR exploded shortly after launch in 2002). While optical methods give a more global picture of the comet, the analysis of individual dust particles has resulted in the identification of some organic molecules, which may have played an important, steering role in the origin of life processes on the Earth. [ABSTRACT FROM AUTHOR]