Comets and the Origin of Life: Proceedings of the Fifth by Fred L. Whipple (auth.), Cyril Ponnamperuma (eds.)

By Fred L. Whipple (auth.), Cyril Ponnamperuma (eds.)

The go back of Halley's Cornet in 1986 has generated a lot ex­ citement within the medical neighborhood with arrangements already afoot for a global Cornet Watch and a cornet release by means of the eu area group, the japanese and Soviet house Scientists. The meet­ ing held on the collage of Maryland in October 1980 used to be essentially motivated via the arrangements for additional learn of this cornet and by means of essentially the most vital unanswered questions relating to comets, identify­ ly, whether or not they can have made a eontribution to the beginning of lifestyles on the earth. Our un"derstanding of the position of comets within the foundation of lifestyles needs to inevitably come from our stories of the astronomy and the chem­ istry of comets. a few clues to the approaches which resulted in the for­ mation of natural molecules and at last to the looks of existence have come from those experiences of comets, possibly the main historical of all items in our sun approach. even if there's, even if, a biology of comets nonetheless continues to be obvious, even though a few claims were made that maybe comets could themselves supply an atmosphere for even the beginnings of existence. Scientists with the most recent to be had info on comets and differing reviews as to the position of comets within the beginning of lifestyles attended this symposium. The formal papers provided at the moment are being made to be had to the scholars of chemical evolution in the pages of this volume.

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Extra info for Comets and the Origin of Life: Proceedings of the Fifth College Park Colloquium on Chemical Evolution, University of Maryland, College Park, Maryland, U.S.A., October 29th to 31st, 1980

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The largest uncertainty in the application of eq. (1) is in the species lifetime. For most cometary observations, and this is particularll the case in the UV where the species lifetimes give scale lengths ~10 km, the field-of-view is much smaller than the projected size of the coma and instead of the total flux, an average surface brightness is measured. If this is denoted by Bi , measured in Rayleighs, then (2) where Ni is the ave rage column density of the species along the lineof-sight. This must be determined by integrating a suitable model of the density along a line-of-sight at a projected distance p from the nuc Ieus to get Ni(p) and then integrating over the instrumental fieldof-view.

For most cometary observations, and this is particularll the case in the UV where the species lifetimes give scale lengths ~10 km, the field-of-view is much smaller than the projected size of the coma and instead of the total flux, an average surface brightness is measured. If this is denoted by Bi , measured in Rayleighs, then (2) where Ni is the ave rage column density of the species along the lineof-sight. This must be determined by integrating a suitable model of the density along a line-of-sight at a projected distance p from the nuc Ieus to get Ni(p) and then integrating over the instrumental fieldof-view.

4 [AU] Figure 1. The ratio of C2 and CN production rates observed in Cornet West (1975n) as a function of heliocentric distance. The solid line is the prediction of a model in which the C2 parent is trapped in icy grains while the CN parent is in a more volatile matrix. 0 AU. Although varying the assumed parameters in the conversion from column densities to production rate will vary the details of this graph, the sharp discontinuity can not be made to vanish. Note that the discontinuity occurs at that heliocentric distance beyond which water ice does not evaporate rapidly.

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