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fbtwitterlinkedinvimeoflicker grey 14rssslideshare1
Wickramasinghe, Janaki Tara.
Languages: English
Types: Doctoral thesis
The thesis presents a re-evaluation of the theory of panspermia. I show that collisions of comets with Earth and Earth-like planets play a role in transferring microbial life across the galaxy. After a brief overview of panspermia in Chapter 1, Chapter 2 develops the theory of cosmic dust. The extinction curve for the galaxy SBS0909+532 at red shift z=0.83, confirms the organic composition of dust upto distances that are a substantial fraction of the Hubble radius. In Chapter 3 a brief overview of comets is presented. Chapter 4 examines dynamical interactions of the Oort cloud of comets with molecular clouds in the galaxy. Using a numerical integration procedure, including the effect of the galactic tide, we show that such interactions lead to sporadic and recurrent injections of comets into the inner solar system. Chapter 5 examines the fate of comets deflected at the present epoch into the inner regions of the solar system. Estimates of the flux of such comets show that there should be -100 times more comets in Halley-type orbits than are actually observed. This discrepancy can be resolved if comets develop porous, organic crusts of very low albedos. Chapter 6 discusses the expulsion of microorganisms from the solar system and their survival prospects, leading to the conclusion that an adequate fraction survives for re incorporation into exosolar planetary systems. The final chapter considers the problem of liquid water in comets. Arguments for radiogenic melting of primordial comets are re-examined. It is shown that comets with radii > 8km can retain liquid water cores for timescales [text unavailable] after their formation, thus providing sites for amplification of small initial compliments of bacteria. By modelling solar heat flow near perihelion onto a crusted, rotating comet it is shown that transient sub-surface pools can be generated, providing habitats for microbes. Data from Deep Impact for comet Tempel 1 is modelled to show evidence for clays, organics and liquid water, and potential microbial habitats.

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