Visible to thermal-infrared spectrophotometry of a possible inactive cometary nucleus

(20461) 1999 LD31 is one of the few objects with retrograde orbits listed i n the Minor Planet Catalog and thus designated as asteroids rather than com ets. Observations of (20461) 1999 LD31 made in March 2000 with the 10-m Kec k I telescope indicate an optical albedo, p(v), of 0.03 +/- 0.01 and a diam eter of 14 +/- 3 km. The low albedo and results of spectrophotometry carrie d out with the University of Hawaii 2.2-m and the UK Infrared 3.8-m telesco pes are indicative of a D-type asteroid or cometary nucleus. These results, together with the nature of its orbit, suggest that (20461) 1999 LD31 is a n example of an object originating in the outer Solar System that has evolv ed into an orbit characteristic of a Halley-type comet and may be the nucle us of an extinct or dormant comet. (C) 2001 Academic Press.