Session 16. Asteroid Discovery and Classification
Contributed Oral Parallel Session, Tuesday, October 13, 1998, 9:00-10:40am, Madison Ballroom D

## [16.06] Discovery of Aten Asteroids: Visual Ground-Based vs. Infrared Space-Based

E.F. Tedesco (TSI), K. Muinonen (Univ. Helsinki), S.D. Price, M.P. Egan (AFRL/VSBC)

Aten asteroids are that sub-group of the Near-Earth Asteroid (NEA) population with semimajor axes < 1 AU and aphelia > 0.983 AU. As of 1998 May 24, the observed population is 502, 6% of which are Atens. This is a lower-limit because search programs observe primarily around the opposition point and, for a given size and albedo, Atens are generally fainter than other NEAs at discovery. Thus the Aten population is being seriously under-sampled in current search programs.

If the Aten population is about 25% that of the Apollo population, then their hazard potential is about half that for the Apollos because the impact probability with the Earth for an Aten is twice that for an Apollo (Bottke, {\it et al.}, 1994, {\it Hazards due to Comets and Asteroids}, p. 337, T. Gehrels, ed.). Thus the under-sampling of this population is significant in terms of the goals of the NEO hazard search program.

According to Bowell and Muinonen ({\it Ibid.}, p. 149) it would require 25 years to discover 33% of the Aten population, with diameters larger than 0.5 km, if a 6,000 sq deg/month area within 30 degrees of opposition were searched to V < 22. This would increase to 83% by searching the same area more broadly in longitude. Current surveys cover a few thousand square degrees of sky per month to V \approx 20 and a few hundred square degrees to fainter limiting magnitudes.

Preliminary results of our simulations show that a space-based infrared system would discover (and characterize) over 90% of Atens larger than 0.5 km in a five-year period.