This paper reports new spectraphotometric observations of Earth approaching asteroids depend on their sizes and orbits. Most proachers which may support the weathering hypothesis. They result bodies larger than ศ2 km have reddish colors similar to comfrom an ongoing spectraphotometric survey of Earth approachers con- mon main-belt asteroids of spectral type S. Smaller bodies, and ducted with the 24ะ telescope at Table Mountain Observatory (TMO) in Wrightwood, California, which is owned by the Jet Propulsion Laboratory
those that may have recently migrated from the main belt, have (JPL) of the California Institute of Technology. Opportunities to observe relatively neutral spectra in the 0.5-to 0.8-m wavelength Earth approachers have recently increased, owing to upgrades to the range. These trends may result from the action of ''space-Spacewatch search at the University of Arizona (Gehrels et al. 1996) and weathering,'' recently proposed to explain similar spectral varito the start of the Near-Earth Asteroid Tracking program run jointly by
ations on the surfaces of S-type asteroids and the disparity JPL and the U.S. Air Force (Helin et al. 1997). By reserving ศ5 dark between the colors of ordinary chondrite meteorites and their nights per month over a period of 6 months, and by observing at times probable main-belt parents.