Copyright © 2000 by Near Earth Asteroid Tracking (NEAT)
This image is a combination of three images obtained by the Near Earth Asteroid Tracking (NEAT) program on 2000 April 10.31, April 10.32, and April 10.33. Each image was exposed for about 20 seconds.
During September of 1984, C. T. Kowal (Palomar Observatory, California, USA) was examining photographic plates exposed earlier in the year with the 1.2-m Schmidt telescope, when he found the unmistakable trail of a comet. The trail appeared on images exposed on 1984 April 23.30 and April 30.26. Kowal estimated the magnitude as 15 and described the comet as "almost stellar, with a faint but definite coma." B. G. Marsden quickly realized the Kowal's object was identical to a minor planet found by A. Mrkos (Klet Observatory, Czech Republic) on a photographic plate exposed on May 2.89. Mrkos had noted that the minor planet (designated 1984 JD) was stellar on the first image, but slightly diffuse on the second. The magnitude was given as 16.0.
Only one additional observation was reported. Following the discovery announcement, Mrkos reported that he had photographed the object again on May 19. He gave the magnitude as 16.0.
From the initial positions, Marsden computed an elliptical orbit with a perihelion date of 1984 May 16.04 and an orbital period of 7.21 years. Following the additional positions provided by Mrkos for May 19, Marsden revised the orbit and gave the perihelion date as June 7.63 and the period as 7.32 years.
During August of 1987, S. Nakano reinvestigated the orbit of this comet. He confirmed the correctness of Marsden's earlier orbit and provided a prediction for the comet's return. He gave the likely perihelion date as 1991 July 19.07. He also noted the orbital period had increased to 9.33 years. The webmaster notes this was due to a close approach to Jupiter during March of 1989. The comet was not recovered. Nakano took another look at the orbit during May of 1997 and provided a prediction for the next return. The resulting perihelion date was 2000 November 3.07.
During March of 2000, the Lincoln Laboratory Near-Earth Asteroid Research (LINEAR) project provided observations of an asteroidal object from March 9.30 and March 13.32, which was subsequently designated 2000 ET90. Following additional observations by LINEAR on April 4 and 8, G. V. Williams (Central Bureau for Astronomical Telegrams) noted the apparently cometary orbit and requested further observations. Prediscovery images were subsequently reported by LINEAR for February 7.42 (magnitude 19.2-19.7), and by the Catalina Sky Survey for March 1.32 (magnitude 17.2-17.4). Another observation was subsequently found by the Lowell Observatory Near-Earth Object Search (LONEOS) program for April 2.23 (magnitude 16.9). From the subsequent orbit spanning nearly two months, Marsden suspected this was comet Kowal-Mrkos and an independent suggestion was also made by C. W. Hergenrother. Marsden quickly confirmed that 2000 ET90 was identical to Kowal-Mrkos. He also noted that the prediction for the 2000 return was 125 days too late.