[Previous] | [Session 59] | [Next]
R. P. Binzel (Obs. Paris), S. J. Bus (U. Hawaii), T. H. Burbine (NMNH), L. E. Malcom (Caltech)
The availability of a self-consistent set of visible wavelength CCD spectra for more than 1400 asteroids (Bus 1999, Ph. D. Thesis; Bus and Binzel, submitted) that includes measurements for more than 100 near-Earth objects (Binzel et al., in preparation), provides the basis for an analysis of size dependent spectral properties. Near-Earth objects, by virtue of their proximity, provide the opportunity for spectral measurements of objects at sizes below 100 m. By analyzing the spectral properties of near-Earth objects in conjunction with those for > 100 km main-belt asteroids, we have the ability to identify spectral trends for objects spanning more than 3 orders magnitude in size.
Collisional lifetimes of asteroids are proportional to their size, since larger asteroids are less likely to be disrupted by collisions. Smaller asteroids have shorter collisional lifetimes. Thus smaller asteroids have younger ages than large asteroids and can be expected, on average, to have younger surfaces. Space weathering models that alter an asteroid's surface over time (e.g. Pieters et al. 2000, Met. Plan. Sci. 35, 1101; Sasaki et al. 2001, Nature 419, 555) would predict that smaller asteroids would be the less effected by weathering than larger objects.
In this paper we examine the statistical significance of size dependent trends in asteroid spectral properties and compare significant trends in the data with the what is predictable based on space weathering models. The ability of space weathering models to give results consistent with the data is a key element in evaluating their validity.