Copyright © 1997 by Herman Mikuz (Crni Vhr Observatory, Slovenia)
This image was obtained on 1997 December 28.73 UT with 36-cm, f/6.7 Schmidt-Cassegrain telescope, V filter and CCD. Exposure time was 5 minutes. (Image reversed by Author)
Discovery
Malcolm Hartley (U. K. Schmidt Telescope Unit, Siding Spring, Australia) discovered this comet on 1986 March 15.59. He estimated the magnitude as 17-18 and added that a faint tail was evident. Further images were obtained on March 17.68 and 20.61, whereupon the comet was annnounced to the Central Bureau for Astronomical Telegrams.
Historical Highlights
Upon the arrival of the three initial positions of this comet, D. W. E. Green (Central Bureau for Astronomical Telegrams) computed a "very uncertain" parabolic orbit which indicated the comet had been closest to the sun on 1985 June 20 at a distance of 0.076 AU. The inclination was given as 60 degrees. Green added, "A low-inclination, short-period orbit gives similar residuals." The discovery info, as well as the rough orbit, were published on March 24. On April 8, the Central Bureau published a revised orbit which included the original positions as well as more recent ones acquired on April 5. B. G. Marsden confirmed Green's suspected short-period orbit was the correct one. His calculations indicated the comet had passed perihelion on 1985 June 5 at a distance of 0.961 AU. He said the comet's angular distance from the sun would have been too small to have permitted observations during 1985 and added that the comet appeared to have made a close approach to Jupiter during 1982. The comet remained under observation until June 7. Computations by S. Nakano during 1987 indicated a perihelion date of 1985 June 5.2 and a period of 6.27 years.
Apparition of 1991: Nakano supplied a prediction for the comet's 1991 return, but searches were unsuccessful; however, the comet was accidentally rediscovered on July 9 of that year. G. R. Kastel' (Institute for Theoretical Astronomy) reported on July 11 that T. V. Kryachko (Majdanak) reported the discovery of a comet on images exposed on July 9 and confirmed the find on the 10th. He described it as magnitude 11, with a coma 15 arc minutes across. Nakano suggested this was Hartley 2, which indicated his prediction had been 5.6 days too late. R. E. McCrosky and C.-Y. Shao (Oak Ridge Observatory, Massachusetts, USA) confirmed Nakano's suggestion on July 12 when they photographed the comet with the 155-cm reflector. The comet passed 0.77 AU from Earth around mid-August and passed perihelion on September 11. The comet was brighter than magnitude 10 in late July and was brighter than magnitude 9 by early August. The comet reached a maximum magnitude of 8 during the first half of September and maintained that brightness into October. Thereafter, it faded from 9 in early November to 12 by late December. Thoughout December, the coma was generally 2-3 arc minutes across. The comet was last detected on 1992 May 4, when astronomers at Oak Ridge Observatory obtained two images.
Apparition of 1997: The comet passed perihelion on 1997 December 21 and was closest to Earth on 1998 January 8 (0.8177 AU). The comet was recovered on 1997 May 2 at Whipple Observatory (Mt. Hopkins). It attained a maximum brightness of about 8 at the end of December and the coma was then about 8 arc minutes across. The comet slowly faded as 1998 progressed. Most observers estimated a magnitude near 8.5 on January 20, while the coma diameter was about 7 arc minutes. By mid-February, the magnitude was between 9.5 and 10, while the coma was about 4 arc minutes across. Only a few visual observers were still following the comet by mid-March. In general, the magnitude was then near 11, while the coma was 2 arc minutes across. The comet was last observed on 1999 April 12, when observers at the Lunar and Planetary Laboratory (Catalina Station, Arizona, USA) determined the total magnitude as 19.2.
Apparition of 2004: The comet passed perihelion on 2004 May 17.98, but it was not well placed, as it was lost in the sun's glare when it would have been brightest. Photographic observers caught the comet between magnitude 16 and 17 during September and October of 2004. The comet was last detected on 2005 April 15, when astronomers at the Catalina Sky Survey (Arizona, USA) obtained four images. The comet was then between magnitude 18 and 19.
Apparition of 2010: One of the earlierst predictions for this apparition came from K. Kinoshita in January 2007. He took 564 positions from the comet's apparitions of 1985, 1991, 1997, and 2004, and predicted the comet would pass perihelion on 2010 October 28.27. A prediction by S. Nakano during April 2007 used 615 positions from the apparitions of 1991, 1997, and 2004, and gave the perihelion date as October 28.24. This apparition will be the most favorable since the comet's discovery, as the comet will pass only 0.12 AU (11 million miles) from Earth on 2010 October 20. The comet is expected to reach magnitude 5, which will enable it to be a naked-eye object for observers in very dark skies. The Deep Impact spacecraft, which studied periodic comet 9P/Tempel 1 in 2005, will fly pass 103P/Hartley 2 during the Autumn of 2010, as part of the EPOXI (Extrasolar Planet Observation and Deep Impact Extended Investigation) mission. Because of this upcoming flyby, the comet was observed by the Spitzer Space Telescope on 2008 August 12 and 13. These observations revealed the comet's nucleus was probably around 1.2 km across.
Additional Images
Copyright © 1997 by Masayuki Suzuki (Japan)
This image was obtained on 1997 December 21 with a 20-cm f/9 telescope and a CCD camera. Exposure time was 30 seconds. The image measures 16x12 arc minutes.
Copyright © 1998 by Stefano Sposetti
This image was obtained on 1998 January 5.73 with a 20-cm f/6.3 Celestron and a Hi-SIS22 CCD camera. It is composed of 190 20-second exposures. Sposetti colorized the image to enhance the brightness levels within the coma.
Copyright © 1998 by Masayuki Suzuki (Japan)
This image was obtained on 1998 January 25 with a 20-cm f/9 telescope and a CCD camera. Exposure time was 30 seconds. The image measures 16x12 arc minutes.
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