Research Training Program

Smithsonian Institution
National Museum of Natural History

PROJECT SUMMARY
1997

Gregory A. Dehn
The Colorado College
Colorado Springs, Colorado
Tim McCoy, Ph.D
Glenn MacPherson, Ph.D.
Supervising Scientists
Department of Mineral Sciences
"My eyes were opened to a field of science which I knew little about. I am grateful for the opportunity to explore research in meteoritics."

The History of the Bencubbin Meteorite: A Macroscopic Clast Analysis

ABSTRACT
Bencubbin is a stony-iron meteorite which has, despite attempts, remained unclassified. It is possible, by unraveling the processes forming this enigmatic meteorite, to expand knowledge about physical and chemical conditions in the early solar nebula as well as the nature of primitive materials that accumulated to form planetary bodies. Two scenarios have been offered for the evolution of Bencubbin: formation as a result of processes in the solar nebula, and formation as a result of impact melting on a chondritic parent body. Previous researchers proposed sorting mechanisms which may have existed in the solar nebula resulting inadvertently from processes attributable to aggregation of silicates, irons, and sulfides. Quantifying evidence of such a mechanism in Bencubbin may aid in unraveling the place and processes of its origin. No previous detailed study has been completed in order to clarify and quantify these mechanisms, as well as observations of apparent foliation, which may indicate some type of impact in this meteorites history. A macroscopic study of Bencubbin was completed by tracing ~ 1300 metal and silicate chondrule-like clasts. The major and minor axes of each class was defined by digitizing 4 points. The measurements on these axes were used to calculate area, volume, and mass. Preferred orientations of each class were measured as well. The angle above the horizontal of the major axis defined the orientation of that particular class. Results were plotted on histograms to aid in the observation of sorting mechanisms (size, mass) and any existing foliation. Metal and silicate clasts exhibited no size sorting. However, results indicated sorting by mass. In addition, there seems to be an apparent foliation. Most metal and silicate clasts are aligned at an angle of 85-90 degrees above the horizontal. Although the presence of a sorting mechanism alone cannot determine a nebular origin for this meteorite, it was concluded that the results reinforce current evidence of a nebular origin for Bencubbin, while the apparent foliation appears to indicate a later impact.

This research was made possible by a grant from the Office of the Director, The Smithsonian Institution (NMNH).

Letter of Gratitude