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157P/Tritton

Past, Present, and Future Orbits by Kazuo Kinoshita

G. Sostero image of 157P exposed on 2003 October 16
Copyright © 2003 by Giovanni Sostero (Remanzacco Observatory, Italy)

This image was obtained on 2003 October 16.12 UT with the 0.45-m f/4.5 Newtonian reflector and a CCD camera. Twenty 30-second unfiltered exposures were combined.

Discovery

     Keith Tritton (U. K. Schmidt Telescope Unit, Coonabarabran) discovered this comet on a deep IIIa-J exposure made with the 122-cm Schmidt telescope on 1978 February 11.66. The total magnitude was estimated as 20. An additional image was obtained on February 13.67. Tritton said the comet exhibited a fuzzy nucleus and a tail. Confirmation came from C.-Y. Shao (Harvard Observatory's Agassiz Station) on February 15.28. He said the comet was "very well condensed" with a total magnitude of about 19. A tail extended 10 to 15 arc seconds. Tritton obtained another image on February 15.69.

     This comet was missed at the predicted apparitions of 1984, 1990, and 1996. When the new comet designation system was introduced by the International Astronomical Union in August of 1994, this comet did not receive a "P/" designation for a short-period comet, but received a "D/" designation, which meant "it would be ill-advised or impossible seriously to consider a prediction for a future return...." Nevertheless, predictions were still made at the expected 2003 apparition.
     Using the same handful of observations made during the 32-day period in 1978, S. Nakano predicted a perihelion date of 2003 March 4.04 on Nakano Note No. 412R (1999 May 5). Although monthly alerts were issued to comet observers by Seiichi Yoshida during the first 7 months of the year, no word of this comet came forth--until October. Interestingly, C. W. Juels (Fountain Hills, Arizona, USA) detected a fast-moving object on CCD images obtained with a 0.12-m refractor on October 6.44. His colleague, P. Holvorcem (Campinas, Brazil) co-added three of the unfiltered images and noticed a coma 2 arc minutes across and a faint tail extending 1.5 arc minutes toward about PA 257°. During the next 24 hours the cometary nature was confirmed by numerous other individuals, who also measured precise positions. Maik Meyer (Germany) calculated a rough orbit based on the positions obtained on October 6 and 7, from which S. Hoenig (Germany) noticed a resemblance to the lost comet Tritton. B. G. Marsden (Smithsonian Astrophysical Observatory) was alerted to the possible link and later on October 7 his calculations confirmed that this comet was identical to comet Tritton of 1978. As it turned out, the actual perihelion date for this return was 2003 September 24.31, so that the prediction was over six months too early.

Historical Highlights

  • The first orbit was calculated by M. P. Candy using positions obtained by Tritton on February 11, 13, and 15. It was an elliptical orbit with a perihelion date of 1977 October 30.07 and an orbital period of 7.30 years. B. G. Marsden revised the orbit using five positions spanning the period of February 11 to March 13. He also gave an elliptical orbit with a perihelion date of October 28.51 and an orbital period of 6.33 years.
  • Apparition of 1978: Moonlight made observations impossible during the last half of February and during the early days of March; however, the comet was found by J. H. Bulger (Harvard Observatory's Agassiz Station) on March 10.27. He gave the nuclear magnitude as 20. The last three observations of the comet were obtained by Shao on March 11.28, 13.20, and 14.21. On IAU Circular No. 3194, issued on 1978 March 15, Marsden wrote, "It is possible that the comet experienced an outburst around the time of the Harvard observation on Feb. 15...." No observations were obtained thereafter.
  • The BAA Handbook for 1984 published a prediction by S. Nakano for the upcoming 1984 apparition. Nakano took seven positions obtained during the period of 1978 February 11 to March 14 and applied perturbations by all nine planets. The result was a perihelion date of 1984 March 3.12 and a period of 6.36 years. The comet was not recovered. Later, D. W. E. Green published predictions in the Comet Handbook issued by the International Comet Quarterly. These gave perihelion dates of 1990 July 8.57 and 1996 November 5.02. During 1994, Patrick Rocher also provided a prediction for the 1996 apparition. He gave the perihelion date as 1996 November 4.11 and the orbital period as 6.34 years. Again, the comet was not recovered.
  • Close approaches to planets: The comet experienced six close approaches to Earth and two close approaches to Jupiter during the 20th century. It makes three close approaches to Earth and one close approach to Jupiter during the first half of the 21st century. (From the orbital work of Kazuo Kinoshita)
    • 0.66 AU from Earth on 1920 January 13
    • 0.50 AU from Earth on 1932 December 8
    • 0.32 AU from Jupiter on 1937 May 10
      • decreased perihelion distance from 1.43 AU to 1.32 AU
      • decreased orbital period from 6.54 to 6.23 years
    • 0.48 AU from Jupiter on 1948 April 12
      • increased perihelion distance from 1.32 AU to 1.40 AU
      • increased orbital period from 6.23 to 6.39 years
    • 0.46 AU from Earth on 1951 December 14
    • 0.76 AU from Earth on 1965 January 22
    • 0.86 AU from Earth on 1978 January 30
    • 0.94 AU from Earth on 1991 February 5
    • 0.98 AU from Earth on 2009 October 28
    • 0.26 AU from Jupiter on 2020 February 11
      • increased perihelion distance from 1.36 AU to 1.57 AU
      • increased orbital period from 6.29 to 6.67 years
    • 0.91 AU from Earth on 2035 November 13
    • 0.79 AU from Earth on 2043 January 9

    Additional Images

    C. W. Juels image of 157P exposed on 2003 October 22
    Copyright © 2003 by Charles W. Juels (Arizona, USA)

    This image was obtained by one of the comet's rediscoverers on 2003 October 22.49 UT with the 0.50-m f/4.8 Newtonian reflector and a CCD camera. Twenty-six 1-minute exposures were combined. The image scale is 2.04"/pixel and the field of view is 17.4' by 17.4'. North is up and east to the left.

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