76P/West-Kohoutek-Ikemura
(0076P)
Type: Periodic
Perihelion date: 13 April 2026
Perihelion distance (q): 1.6
Aphelion distance (Q) : 5.3
Period (years): 6.5
Eccentricity (e): 0.54
Inclination (i): 30.5
JPL orbit diagram
COBS lightcurve
Atlas
The events leading up to the discovery of this comet are among the strangest ever
recorded. During January 1975, Richard M. West (European Southern Observatory
Sky Atlas Laboratory, Geneva) was examining plates exposed by Pizarro and
Ballereau at the European Southern Observatory at La Silla (Chile). On a plate
exposed on 15 October 1974, he found a trail, which he described as diffuse, with a
magnitude of 12. The comet also exhibited a central condensation and a tail less than
one degree long. Searches through other ESO plates revealed no trace of the comet
and West was left with a single image taken three months earlier and showing
ambiguous motion (either to the east-southeast or west-northwest). The comet was
presumed lost.
Near the end of February of 1975, Lubos Kohoutek (Hamburg Observatory, Germany)
found a cometary object on a plate exposed on 9 February. As the motion was
ambiguous, he began searching for this comet on 27 February in areas southwest
and northeast of the 9 February position. Kohoutek found a comet to the southwest
on a photograph exposed on 27 February. He estimated the magnitude as 13 and
described the comet as diffuse, with a condensation. On 2 March, word came from
Japan that Toshihiko Ikemura (Shinshiro) was not able to find Kohoutek's comet in the
extrapolated position, but he had discovered a comet on 1 March, at a position
northeast of Kohoutek's 27 February position. He estimated the magnitude as 12, and
his confirmation on 2 March revealed it heading in the opposite direction to
Kohoutek's reported comet.
B. G. Marsden began examining the February positions and immediately noted that
when Ikemura's comet was extrapolated backwards it aligned almost perfectly with
Kohoutek's 27 February comet. Thus, while attempting to confirm the 9 February
comet, Kohoutek found a second one which was independently found by Ikemura.
The 9 February object was latter photographed and became known as 75P/Kohoutek.
Additional images of comet Kohoutek-Ikemura were obtained at several observatories
during the next week. K. Hurukawa and T. Hirayama computed the first parabolic
orbit, which was published on 3 March. It indicated a perihelion date of 23 March
1975, a perihelion distance of 0.940 AU, and an inclination of 13.0°. After a few more
days of observations had been received, Marsden began his orbital computations and
soon noted that comet Kohoutek-Ikemura was identical to the comet West had found
on the October plates. The comet became officially known as West- Kohoutek-
Ikemura.
The comet's elliptical nature was first established by B. G. Marsden on 7 March 1975,
following the link of the February and March observations to that of October. Marsden
commented, "It is also clear that the comet passed only 0.01 AU from Jupiter in March
1972." Later computations by G. W. Kronk using a more precise orbit revealed the
comet passed 0.012 AU from Jupiter late on 22 March 1972. Prior to the comet's entry
into Jupiter's sphere of influence during the latter half of 1971, the comet moved in an
elliptical orbit with a period of about 30 years and a perihelion distance of 4.78 AU.
The comet returned to perihelion in 1981. Computations by S. W. Milbourn during
1980 predicted the perihelion date would be 12 April. H.-E. Schuster recovered the
comet on 12 November 1980 and the measured position indicated a correction of -
1.37 days needed to be applied to Milbourn's prediction. This was not an especially
favorable apparition as the comet reached a maximum brightness of only 17.
The comet was also seen at its returns in 1987 and 1993. The latter return was rather
favorable as observers reported maximum magnitudes slightly brighter than 13. The
comet made a very close approach to Mars on 5 June 2000, with Kenji Muraoka
(Japan) giving the smallest distance between the comet and Mars as 0.04215 AU,
which is equal to 3,914,000 miles or 6,303,000 kilometers. Although this comet has
been bright enough for large amateur telescopes to see in the past, this close
approach was not observable by even the largest telescopes as the comet was then
situated less than 7° from the sun. The comet was recovered on 2006 August 30 by
Peter Birtwistle (Great Shefford Observatory, England). He gave the nuclear
magnitude as 18.8.
Observations (VEMag = visual equivalent magnitude)
Date
10x10 mag
Error
VEmag
Coma '
29-Oct-19
18.52
0.08
18.3
0.2
30-Nov-19
18.21
0.11
17.4
0.3
08-Dec-19
18.36
0.15
17.1
0.3
21-Dec-19
18.04
0.02
17.4
0.3
28-Dec-19
18.07
0.05
16.7
0.4
04-Jan-20
18.63
0.21
17.6
0.3
30-Jan-20
18.44
0.08
17.7
0.3
15-Feb-20
19.53
0.13
18.5
0.2