Cosmochemistry is the study of the composition of extraterrestrial materials and of the chemical processes occurring in space. Examples of the many questions cosmochemists traditionally deal with are the formation and abundance of the elements, the nature and origin of interstellar molecules, and the origin and evolution of the solar system. Meteorites are ancient relics of the processes which formed the planets; they may even contain traces of interstellar material. They therefore afford the best means for the laboratory-based chemist to address some of the major questions in Cosmochemistry
The Cosmochemistry group at Arkansas is a founding member of the Arkansas Center for Space and Planetary Sciences. The center currently houses about five research groups in Arkansas and two at Oklahoma State University, a number that is rapidly growing, who work closely together on a variety of problems in space and planetary science including the design of instruments for optical dating to be placed on spacecraft and the Hera mission to take samples from three near-Earth asteroids. The center houses a unique planetary environmental chamber for simulating conditions on Mars, comets and asteroids, and it operates a large number on ancillary scientific instruments like electron microscopes, gamma counting spectrometers, thermoluminescence detectors and a cathodoluminescence microscope.
The thermoluinescence technique involves the measurement of light produced by a sample as it is heated, and is widely used for radiation dosimetry and dating. A closely related technique is cathodoluminescence, in which the production of light is stimulated by an electron beam. The group has pioneered the use of these luminescence techniques in the study of meteorites. The approaches have proved particularly successful when applied to the ancient and least altered meteorites. We have found that we can identify unaltered meteorites and investigate the effects of any parent body heating, even at the mildest levels of thermal alteration.
We are now working with colleagues at OSU to develop the technique for in situ operation on Mars landers. We also pursue dosimetry-related properties of meteorite thermoluminescence. Several hundred meteorites, many of which fell 100,000 years ago, are brought back from the Antarctic each year. Natural thermoluminescence levels provide an indication of how long each meteorite has been on earth and of whether the meteorite experienced an unusual radiation history in space. In recent years, working closely with the Johnson Space Center who are responsible for handling the returned meteorites, the group has become involved in the initial screening procedure for the meteorites prior to them being made generally available to the scientific community.
Professor Sears is the Editor of the journal Meteoritics and Planetary Science, Journal of the Meteoritical Society, and Director of the Arkansas Center for Space and Planetary Science.
For the graduate student, research in the cosmochemistry group provides an opportunity to make contributions to an exciting and rapidly advancing multidisciplinary field, and to develop expertise in a number of areas of chemistry which are of value to industry and academia.