Observational Study of the Rotation Rates of Very Small Near-Earth Asteroids

New Mexico Institute Of Mining And Technology, Socorro NM

Investigators

Abstract

AST-0908868 Eileen Ryan This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This project is motivated by our lack of knowledge of the physical properties of the very smallest Near-Earth Asteroids (NEAs) now being discovered. This is particularly true for rotation periods, which can provide information about an asteroid's internal composition, degree of fracture, and collisional history. Current data suggest that NEAs smaller than 200 meters in diameter rotate faster than 2.2 hours, which is the theoretically derived critical rotation limit for strengthless ellipsoids, while larger bodies rotate more slowly. This suggests that the small fast rotating objects are solid and so are likely to be individual fragments that once made up a rubble pile parent body that was disrupted by a catastrophic impact. However, the sample size of small asteroids with known rotation periods is small and a more robust statistical sample is needed. The state-of-the-art 2.4-meter telescope at the Magdalena Ridge Observatory will be used to determine rotation periods (through light curves) and material classifications (through spectrophotometry) for 15-20 small NEAs per year. By the end of the three year project, the number of characterized small NEAs is expected to have more than doubled. If, as suggested by preliminary observations by the PIs, a large percentage of slowly rotating small bodies exists, it may well be the case that "rubble piles" (versus monolithic or coherent bodies) are common at the low-mass end. Such a result is important in assessing and planning for the threat posed by these objects. The project will be carried out at a minority serving institution and provide research and training experiences for these students (though no direct support is included here). The researchers will include Near-Earth Asteroid observations and the concepts involved in this research as part of a Masters of Science Teaching program for K-12 educators, and they routinely give public talks on these topics.