The Oort Cloud in the Galactic Context

University Of Washington, Seattle WA

Investigators

Abstract

AST 0709191 Quinn Since the Oort comet cloud extends to 1/3 the distance to the nearest stars, there is a strong connection between the galactic environment and the evolution of this cloud. Indeed the spike in semi-major axis distribution of observed new comets is due to the more significant torquing of more distant comets by passing stars and the Galactic tide as a whole. Given this connection, changes in the Galactic environment due to the orbit of the Sun in the Galaxy and drifting of the Sun from its formation environment will have significant effect on the distribution of comets in the Oort cloud and the subsequent delivery of those comets to the inner Solar System. In this research program, Dr. Thomas Quinn and colleagues will first study the formation and evolution of the Oort Cloud over the 4.5 billion years of the Solar System's history assuming a number of different star forming environments. It is quite likely that the Sun formed in a dense stellar cluster, but the actual densities and timescale for leaving the cluster are uncertain. The work will consider a number of stellar densities and cluster dissipation timescales and compare the resulting Oort Cloud and subsequent comet shower strength with a control case with no cluster environment. The Solar System, however, does not occupy a static place within the Galaxy. The research will therefore go on to incorporate changes in Galactic perturbations as the orbit of the Sun in the Galaxy evolves. This will be accomplished in the context of a cosmologically motivated model of the Galaxy formed via hierarchical merging in a Cold Dark Matter (CDM) Universe. This model has been calculated using the research group's massively parallel cosmological code, GASOLINE, and the model has been shown to produce many observed characteristics of spiral galaxies. The evolution of the Oort Cloud will be calculated as it feels the perturbations of the gas, stars, and dark matter from the disk, spiral arms and other substructure that exists in the galaxy model. The study will pay particular attention to the subsequent changes to the comet flux into the inner Solar System and possible consequences for impact rates on the Earth. Ever since the connection was made between the extinction event at the end of the Cretaceous and a comet impact, a strong connection has been made between comets and the disciplines of Paleontology and Geology. Both Dr. Quinn and the graduate student supported on this award are part of the University of Washington's Astrobiology program and therefore, will be connecting their research to work done by biologists and geologists in that program. The connection between orbital dynamics and comets also engages the public at large. The issues of the origin of our planetary system, how it fits into the galaxy as a whole and the implications for life are issues that draw the public into the results of dynamical research. Dr. Quinn and the graduate student will incorporate their results into their undergraduate classes and public lectures. ***