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95P/Chiron

Past, Present, and Future Orbits by Kazuo Kinoshita

A. Nakamura image of 95P exposed on 1997 March 31
Copyright © 1997 by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan)

This CCD image was taken on 1997 March 31, using a 0.60-m f/6 Ritchey-Chretien telescope.

Discovery

     "Slow Moving Object Kowal" was announced by Brian G. Marsden on IAU Circular 3129 (1977 November 4), and was to become one of the most interesting objects found during the 1970s. C. T. Kowal (Palomar Observatory, California, USA) said he had photographed a very slow-moving object with the 122-cm Schmidt telescope. The object was found on a plate exposed on 1977 October 18.38 and was confirmed on another plate exposed with the same telescope on October 19.43. A prediscovery image was immediately found by T. Gehrels on a plate exposed with the same telescope on October 11.42 and 12.42. All of the images showed a stellar object, with Kowal estimating the magnitude as 18.0 and Gehrels estimating it as 19.0. Marsden noted, "The motion, scarcely greater than that of Uranus, is extraordinarily slow for an object so close to opposition."

Historical Highlights

  • Additional images were obtained at Palomar on November 3 and 4, enabling Marsden to compute the first orbit on November 8. He considered the orbit "extremely indeterminate" because of the slow motion. Marsden's orbit was based on an assumed low eccentricity and indicated a perihelion date of 1946 June 25.5, a perihelion distance of 15.84 AU, and an orbital period of 66.1 years. Although a high eccentricity orbit was not ruled out at that time, additional observations on November 9 and 10 indicated this was not possible and the original orbit was still considered best.
  • Observations obtained through November 13 indicated the object was probably just past aphelion and a new orbit was computed by Marsden, which enabled Kowal to find images of the object on plates he had exposed with the 122-cm Schmidt telescope on 1969 September 10 and 11. These positions allowed Marsden to further refine his orbit, which revealed a perihelion date of 1996 February 13, a perihelion distance of 8.51 AU, and an orbital period of 50.70 years. Marsden said it was possible for the object to reach magnitude 14.5 and attempts were being made to look for further images around the time of the previous perihelion passages in 1945 and 1895. IAU Circular 3147 (1977 December 5) announced that prediscovery images had been found on plates exposed at Bloemfontein, South Africa on 1941 January 23 and 1943 March 8. The magnitude was estimated as 15. In addition, an image was found on a Palomar Sky Survey plate exposed on 1952 August 23 (magnitude 17) and on a plate exposed at Harvard's Agassiz Station on 1976 November 17 and December 16. IAU Circular 3151 (1977 December 13) then announced a position found on a Harvard survey plate obtained at Cambridge, Massachusetts on 1895 April 24. From all the available positions, Marsden determined the object was presently moving in an orbit with a perihelion date of 1996 February 19.53, a perihelion distance of 8.51 AU, and an orbital period of 50.68 years.
  • Basic observations were made during the next couple of years, but J. Degewij (Jet Propulsion Laboratory, California, USA), D. P. Cruikshank and R. W. Capps (University of Hawaii, USA), and W. K. Hartmann (Planetary Science Institute) made an interesting observation with the NASA IRTF Telescope at Mauna Kea during December 1980 and February 1981. They determined the average brightness and colors and concluded, "These colors rule out water ice as the dominant surface material and strongly suggest a dark, stony surface material, as found on many outer-solar-system bodies."
  • Although the exact nature of Chiron had been debated over the years, an interesting announcement came during 1988. IAU Circular 4554 (1988 February 24) included a statement by D. J. Tholen (University of Hawaii, USA), Hartmann, and Cruikshank (Ames Research Center) indicating an apparent outburst in brightness had occurred. Their observations on 1988 February 20, 21, and 22 showed the comet 0.7-magnitude brighter than expected. They added that no coma could be observed and a spectrum revealed no emission features, but they urged that other astronomers make observations. The outburst was quickly confirmed by other astronomers. Interestingly, Cruikshank, Hartmann, and Tholen made observations during 1988 September and found the outburst had intensified to 1.05-magnitude brighter than normal, but still noted no unusual emissions.
  • Chiron is a comet! Observations made by K. J. Meech (University of Hawaii) and M. J. S. Belton (Kitt Peak National Observatory, Arizona, USA) were announced on IAU Circular 4770 (1989 April 11). Made with the KPNO 4-m telescope on April 10, the CCD images revealed a coma which extended about 5 arc seconds toward the southeast. Further observations of the coma by Meech on 1989 December 27 revealed it was extending about 10 arc seconds toward the northwest.
  • Additional Images

    Michael Brown image of 95P
    Copyright © 1996 by Michael Brown (University of Melbourne)

    The three images of this animation show the asteroidal appearance of 95P/Chiron as it moves across the starry background. The images were obtained by Michael Brown using the 40-inch telescope at Siding Spring Observatory. A period of 2.5 hours elapsed between each image, so the animation represents 95P/Chiron's movement during 5 hours.


    Giovanni Dal Lago image of 95P exposed on 1996 January 20
    Copyright © 1996 by Giovanni Dal Lago

    Giovanni Dal Lago (Italy) took this image on 1996 January 20.03 UT, using a 0.28-m f/5.2 Celestron and a Starlight Xpress SXF CCD camera.


    Masayuki Suzuki image of 95P exposed on 1998 June 20
    Copyright © 1998 by Masayuki Suzuki (Japan)

    This image was taken on 1998 June 20.60, using a 0.20-m f/9 telescope and a CCD camera. The image is a 60-second exposure. The frame measures 16 by 12 arc minutes.

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