William S. Burgett (Institute for Astronomy, University of Hawaii), Nicholas Kaiser (Institute for Astronomy, University of Hawaii)
Keywords: Astronomy
Abstract:
As part of an effort to obtain astrometric data on newly discovered Near-Earth Asteroids (NEAs) using the Magdalena Ridge Observatory s (MRO) 2.4-meter telescope, a program has also been implemented to obtain physical characterization information on some of the smallest objects in the asteroid population. Characterization studies that determine physical properties such as spin rates and orientations, shapes, material type and internal structure/strength are important for properly addressing and mitigating any potential threats from dangerous Earth-crossing objects. The rotation rate of an object can imply essential information about its internal composition (via deduction of strength boundary limits) and degree of fracture, and thereby its collisional history. In particular, the discovery of asteroids having sub-hour rotation periods is highly indicative of a non-negligible tensile strength. Previously, extensive work had been done to acquire rotation rates for asteroids greater than 200 meters in diameter, and although progress has been made extending this database to the less than 200 meter size-range, the data are still lacking. Therefore, our research has been focused toward collecting lightcurves of objects primarily smaller than 200 meters which have allowed the determination of rotation rates.
Rotation rates derived from the lightcurves collected to date indicate that the asteroids studied in this small size regime exhibit both slow (hours) and fast (minutes) rotation periods. With respect to superfast rotators, one object in our database of special note is asteroid 2009 BF2 ( approximately 27 meters in diameter) which is the second fastest rotator yet discovered, with a rotation period of about 58 seconds (2008 HJ is the fastest rotator at 42.7 seconds). Additionally, our survey has collected three lightcurves for objects with absolute magnitudes H > 22 that have been observed to be rotating more slowly (greater than 7 hours) than the presumed strengthless body limit. Asteroid 2008 UP100 exhibits an amplitude of ~1.2 magnitudes or greater even after correcting to zero phase. Recent modeling of rubble pile structures by Harris et al. (2008) indicates that this borders on or exceeds the elongation limit of a slowly rotating strengthless object, implying the possible existence of tensile strength. We expect that the continued photometric observation of faint NEA targets-of-opportunity will increase our current sample and ultimately result in a better understanding of the structure of these small bodies.
Date of Conference: September 1-4. 2009
Track: Astronomy