Courtesy of NASA/JPL/Caltech
This image is the highest resolution image obtained during the flyby of the space probe Deep Space 1 on 2001 September 22.
Alphonse Louis Nicolas Borrelly (Marseilles, France) discovered this comet during a routine search for comets on 1904 December 28. It was then situated within Cetus and was moving northward. Borrelly described it as 1 to 2 arc minutes across, with a small, faint nucleus.
The comet was widely observed during January 1905, with the maximum magnitude reaching about 9 early in the month. In addition, the coma diameter was typically near 2 arc minutes, while a tail length of 10 arc minutes was reported. The comet was followed until May 25, at which time the magnitude had declined to 14.5. R. G. Aitken (Lick Observatory, California, USA) computed an elliptical orbit early in February which indicated an orbital period of 7.30 years. By the time observations ceased astronomers had determined the comet passed perihelion on 1905 January 17. The perihelion distance was determined as 1.395 AU, and the orbital period was 6.91 years.
Predictions by G. Fayet (Paris Observatory, France) enabled H. Knox Shaw (Khedivial Observatory, Helwan) and Alexandre Schaumasse (Nice Observatory, France) to recover the comet on 1911 September 20.05 and 20.16, respectively. It was then estimated as near magnitude 13. This turned into a particular favorable apparition, with the maximum brightness reaching 8.4 during December, thanks to a close approach to Earth (0.53 AU) during that month. In addition, the greatest reported tail length was 30 arc minutes.
Orbital investigations have indicated the comet was placed into its discovery orbit by a series of moderate close approaches to Jupiter during the 19th century, namely in 1817, 1853, and 1889. The comet's orbital period at discovery (6.9 years) caused it to arrive at perihelion roughly one month earlier at each succeeding apparition. This caused the discovery apparition, as well as those of 1911 and 1918 to be very favorable, while those that followed became progressively worse. The maximum magnitude at the 1925 return was 10, while in 1932 it only reached 11.
Another moderately close approach to Jupiter during 1936 nudged the orbital period up to 7.0 years, which virtually locked it into a pattern of very unfavorable returns during the next few returns. Subsequently, the comet was not detected during its 1939 and 1946 returns. Conditions were still poor for the 1953 return, but Elizabeth Roemer managed to photograph the comet nearly 7 months after perihelion, after it had cleared the sun's glare. It was then estimated as magnitude 18.5. Although conditions were just as unfavorable at the 1960 and 1967 returns, Roemer's recovery enabled the orbit to again be precise enough to enable an earlier recovery and the maximum observed magnitudes were 15 and 16, respectively.
The comet experienced another moderately close approach to Jupiter during 1972 which reduced the orbital period to 6.8 years. This made the 1974 return one of the worse, and the maximum observed magnitude only reached 18.0. On the other hand, the 1981 return became one of the most favorable apparitions, with maximum magnitudes reaching 8.7. This also became the most photographed appearance of this comet, up to that time, and observers reported the tail attained a length of about one degree. The 1987 return was very similar to the 1911 return, and maximum reported magnitudes reached 7.5, while tail lengths reached three-fourths of a degree and coma diameters topped out near 10 arc minutes. The 1994 return was not quite as good, with maximum magnitudes only reaching 8.0.
The comet was also scutinized by the Hubble Space Telescope (HST) during the 1994 apparition. Philippe Lamy (Laboratoire d'Astrophisique de Marseille CNRS, France) was the principal investigator of the HST comet nucleus detection project.
The comet's return in 2001 is another favorable one, with the comet predicted to attain a maximum magnitude of 10 during September. The comet came under widespread observation by amateur astronomers during July 2001, when the magnitude was near 13 and by the beginning of August it had steadily brightened to magnitude 11. During this same period of time, the comet's coma increased from a diameter of about 1 arc minute to just over 2 arc minutes. By mid-September, observers indicated a magnitude between 9.5 and 10.5.
An especially important note about the 2001 apparition is that this comet became only the second comet to be photographed up close by a space probe, when Deep Space 1 flew about 1350 miles from the nucleus on September 22. Pictures of the nucleus revealed it measured 5 miles long and about 2.5 miles wide. As the probe approached the comet a sharply defined jet about 60km long was detected extending toward the sun. As the probe moved closer this jet was resolved into three columns or jets, and at its closest, the probe revealed the jets were emanating from bright, smooth patches on the surface. The primary jet appears to emanate from the rotation axis. It was mentioned that there were signs that the jets were eroding away at the surface and creating basins. It was suggested that since the erosion is occuring along the rotation axis, this might eventually cause the comet to split.
Close approaches to planets: The comet experienced six close approaches to Earth and two close approaches to Jupiter during the 20th century. It will make two 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)
- 0.89 AU from Earth on 1904 December 4 (contributed to comet's discovery)
- 0.51 AU from Earth on 1911 December 7
- 0.48 AU from Earth on 1918 December 7
- 0.97 AU from Earth on 1925 December 14
- 0.54 AU from Jupiter on 1936 March 26
- increased perihelion distance from 1.39 AU to 1.44 AU
- increased orbital period from 6.87 to 6.98 years
- 0.61 AU from Jupiter on 1972 February 6
- decreased perihelion distance from 1.45 AU to 1.32 AU
- decreased orbital period from 6.99 to 6.76 years
- 0.48 AU from Earth on 1987 December 7
- 0.62 AU from Earth on 1994 December 5
- 0.44 AU from Jupiter on 2019 May 14
- decreased perihelion distance from 1.35 AU to 1.31 AU
- decreased orbital period from 6.83 to 6.57 years
- 0.41 AU from Earth on 2028 December 6
- 0.62 AU from Earth on 2035 December 2
Copyright © 1994 by Kazuyuki Ito (Sengamine Observatory, Japan)
This image was obtained on 1994 November 4.67 UT with the 20-cm, f/6.0 reflector and an ST-6 CCD. Exposure time was 180 seconds. (Permission to use image was granted by Fukuhara Naohito)
Copyright © 1994 by Gerald Rhemann (Austria)
This image was obtained on 1994 December 3.01 UT with the 171/200/257mm Schmidt camera. Exposure time was 7 minutes and the photographic emulsion was hypered Technical Pan 6415. The image has been cropped by the webmaster to save space.
Copyright © 1994 by Herman Mikuz (Crni Vrh Observatory, Slovenia)
This image was obtained on 1994 December 15 UT with the 20-cm, f/2 Baker-Schmidt telescope, V filter and CCD. Exposure time was 5 minutes. (The webmaster has cropped the image and converted it to black and white to save space.)
Copyright © 2001 by Konrad Horn (Salem, Germany)
This image was obtained by Konrad Horn on 2001 August 29. It is a combination of 30 60-second exposures obtained with a Gensis 100/500 telescope and an AUDINE CCD camera.
Copyright © 2002 by Giovanni Sostero (Remanzacco, Italy)
This image was obtained by Giovanni Sostero on 2002 February 17. He combined 4 300-second exposures obtained with a 0.31-m f/2.8 Baker-Schmidt telescope and a Hi-Sis 24 CCD camera.