U.S.-Japan Cooperative Science: The Origin of Strong X-Ray Emission from Comets

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0300708StancilThis award supports a two-year international collaborative research project between Professor Philip Stancil of the University of Georgia and Professor Kazuhiko Okuno of the Tokyo Metropolitan University in Japan. They will undertake a study on the origin of strong x-ray emission from comets. X-ray emissions by comets have long been puzzling, and a variety of theories have been put forward to explain these emissions. Indeed, electron capture of heavy solar wind ions to highly excited states following collisions with cometary neutrals seems perhaps the most viable explanation. The current topic involves a redirection from studies of ion-atom to ion-molecule collisions and is motivated by observations starting in 1996 of cometary x-ray emission (CXE). The currently favored mechanism for these emissions suggest that they originate from highly-excited, high-charge-state, heavy ions whose levels are populated through charge changing collisions of solar wind ions with neutral molecules (H2O, CO, and CO2) in the comet. Progress in understanding this phenomenon is, however, severely hindered by the deficiency of the available charge transfer (CT) data for molecules, both total and state-selective. The project will involve both theoretical and experimental researchers to investigate CT reactions relevant to CXE. Theoretical studies of highly-charged ion collisions with molecules have received very little attention so that now such investigations are at the forefront of atomic collision theory. Experimental work will evolve into state-resolved measurements and investigation of new neutral targets all advancing the broader area of atomic collisions. The project brings together the efforts of laboratories that have complementary expertise and research capabilities. The research will have an impact on the understanding of x-ray emission phenomena from solar system bodies. It will contribute to understanding and interpreting the increasing number of x-ray observations of comets. It may also contribute to a better understanding of anomalous cosmic ray capture in magnetospheres, and space weather such as a direct probe of the solar wind. The project advances international human resources through the participation of a number of postdocs. Through the exchange of ideas and technology, this project will broaden our base of basic knowledge and promote international understanding and cooperation. Results of the research will be disseminated at scientific meetings and in scientific journals. The research will also contribute to the production of a world wide web accessible database of charge transfer reactions.