73P/Schwassmann-Wachmann
(0073P)
TRY AGAIN 2027
Type: Periodic
Perihelion date: 25 August 2022
Perihelion distance (q): 1.0
Aphelion distance (Q) : 5.2
Period (years): 5.4
Eccentricity (e): 0.69
Inclination (i): 11.2
JPL orbit diagram
COBS lightcurve
Friedrich Carl Arnold Schwassmann and Arno Arthur Wachmann (Hamburg
Observatory, Bergedorf, Germany) discovered this comet on photographs exposed for
a minor planet survey on 2 May 1930. The comet was then described as diffuse and
magnitude 9.5. A few days later, H. Schneller (Berlin-Babelsberg Observatory,
Germany) found prediscovery images on photographic plates exposed on 27 and 29
April.
The comet is intrinsically faint and, when combined with the slight variation in the
computed orbital period and a very unfavorable apparition at its first predicted return
in 1935-1936, it became lost after the 1930 appearance. Searches during the next
several apparitions failed to locate the comet. Further complicating things was an
approach to within 0.9 AU of Jupiter during October 1953 and 0.25 AU in November
1965.
Revised orbital computations by Belyaev and Shaporev in 1973 led to the recognition
that although the apparition of 1974 would be very unfavourable, the comet's return in
1979 would be the most favorable since 1930. J. Johnston and M. Buhagiar (Perth
Observatory, Australia) reported the discovery of a comet on plates exposed during a
minor planet survey on 13 August 1979. Confirmation was made on 15 August and M.
P. Candy (Perth Observatory) noted the comet's direction and rate of motion
resembled what was expected for the lost comet Schwassmann-Wachmann 3. This
was confirmed and the comet's perihelion date was found to be 34 days later than
predicted. The comet attained a maximum magnitude of 12.5 as it passed closest to
Earth (1.4359 AU) on 19 March.
The comet was missed during the 1985-86 apparition, but was observed in 1990. This
was the best appearance since 1930. On April 17, the comet passed 0.3661 AU from
Earth and reached a maximum magnitude of 9. The 1995 appearance was not
supposed to be a very good one with the comet's closest approach to Earth on 1995
October 17 (1.3114 AU) being nearly 1 AU further than the exceptional 1990
apparition. The comet was meeting the expectations of astronomers when it was seen
by K. Kinoshita (Japan) on August 19 at magnitude 12.9, but then something
happened. Astronomers using the Nancay Radio Telescope were monitoring the
comet's emissions during early September, just after the comet's minimum elongation
from the sun on 31 August (40 degrees), when they detected an increase in OH on 8
September. The emissions continued to increase through the 13th. By the 17th, the
comet had moved far enough out of the sun's glare to enable visual observations and
the brightness was found to be magnitude 8.3. That brightness more or less held until
the beginning of October, when several observers reported it had increased to
magnitude 6. Although the comet was still in twilight and at a low altitude, it was then
visible in binoculars as a slightly diffuse star. The comet faded slightly thereafter and
then underwent a third outburst back to 6.3 on 22 October. The comet faded very
slowly after its last outburst. Although it was then moving away from both the sun and
Earth, observers continued reporting the total magnitude as 7.5 to 8 through the end
of November and 8 to 8.5 through the first two- thirds of December. The comet
became more diffuse during the remainder of December and into January and a rapid
fading finally set in during the latter month. By February the brightness had dropped
back to magnitude 14.
Another surprise came in December when observatories began reporting mulitple
nuclei within the coma of the comet. Four nuclei were officially designated and were
labeled "A", "B", "C", and "D"; however, "D" was not observed elsewhere and may
have been a very short-lived condensation. Three additional condensations were
reported, but not designated, because they were also not seen elsewhere.
Component "A" was discovered on 23 December 1995 and was last detected on 18
February 1996. Component "B" was discovered on 23 December 1995 and was last
detected on 14 December 1996. Component "C" turns out to be the main body of the
comet and was followed until 14 December 1996. Z. Sekanina published an article in
the International Comet Quarterly (2005) that offers an excellent argument that the
observations attributed to component "B" during 1996 may actually belong to two
different components. He suggests "B" was seen up to the time the comet became
lost in the sun's glare after February, while component "E" was seen from September
to December. Since "E" was officially discovered i n 2000, this could be considered
prediscovery observations.
The comet's next return to perihelion occurred on 27 January 2001. Although it was
poorly placed for observation, the comet was again widely observed because it was
brighter than expected. In addition, two of the nuclei seen in 1995 were back:
Component "C" was recovered 5 January 2000 and was observed until 20 November
2001, while Component "B" was recovered on 19 November 2000 and was observed
until 27 July 2001.
At the next predicted perihelion date of 7 June 2006 the comet would pass 0.0735 AU
from Earth on 13 May, being only slightly farther away than during the original
discovery apparition of 1930. C. W. Hergenrother (Lunar and Planetary Laboratory)
recovered the brightest component, referred to as "C", while using the 1.2-m reflector
at Mount Hopkins on 22 October 2005. He gave the magnitude as 19.3 and said the
strongly condensed coma was 6 arcsec across. There was also a fan-shaped tail
extending 8 arcsec in PA 300°. Component "B" was found at by J. A. Farrell (Jemez
Springs, New Mexico, USA) on 2 January 2006, while using a 41-cm reflector. He
gave the magnitude as 18.8-19.0, which was then just over three magnitudes fainter
than component "C". The next component found did not match the prediction for any
previously observed component and set the stage for many new discoveries as the
comet approached perihelion. This new component was labelled "G". It was
independently found by R. A. Tucker (Tucson, Arizona, USA) on February 20 and 22,
and E. J. Christensen on Mt. Lemmon Survey images obtained on 24 February. The
magnitude was given as 17.2. Numerous other components were found in the weeks
that followed.
Currently there are 67 components. The major fragments of this comet are "B", "C",
"G", and "R", with "C" being the main comet.
Observations (VEMag = visual equivalent magnitude)
Date
10x10 mag
Error
VEmag
Coma '
10-Jan-17
15.60
0.07
14.1
0.5
27-Jan-17
14.93
0.05
13.2
0.4
06-Feb-17
14.68
0.06
12.7
0.4
20-Nov-17
18.22
0.06
16.7
0.2
10-Mar-22
17.80
0.06
17.8
0.4
24-Mar-22
17.7
0.4
30-Mar-22
17.3
0.4
26-Apr-22
17.4
0.4
23-May-22
16.56
0.04
16.7
0.4
13-Nov-22
12.0
3.2
21-Nov-22
11.5
4.1