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IAUC 5800: 1993e

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                                                  Circular No. 5800
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM     EASYLINK 62794505

     Almost 200 precise positions of this comet have now been reported,
about a quarter of them during the past month, notably from CCD images
by S. Nakano and by T. Kobayashi in Japan and by E. Meyer, E. Obermair
and H. Raab in Austria.  These observations are mainly of the "center" of
the nuclear train, and this point continues to be the most relevant for
orbit computations.  Orbit solutions from positions of the brighter
individual nuclei will be useful later on, but probably not until the
best data can be collected together after the current opposition period.
At the end of April, computations by both Nakano and the undersigned were
beginning to indicate that the presumed encounter with Jupiter (cf. IAUC
5726, 5744) occurred during the first half of July 1992, and that there
will be another close encounter with Jupiter around the end of July 1994.
Computations from the May data confirm this conclusion, and the following
result was derived by Nakano from 104 observations extending to May 18:

                    Epoch = 1993 June 22.0 TT
     T = 1998 Apr. 5.7514 TT          Peri. =  22.9373
     e = 0.065832                     Node  = 321.5182  2000.0
     q = 4.822184 AU                  Incl. =   1.3498
       a =  5.162007 AU    n = 0.0840381    P =  11.728 years

This particular computation indicates that the comet's minimum distance
Delta_J from the center of Jupiter was 0.0008 AU (i.e., within the Roche
limit) on 1992 July 8.8 UT and that Delta_J will be only 0.0003 AU
(Jupiter's radius being 0.0005 AU) on 1994 July 25.4.

     As noted on IAUC 5726, the positions of the ends of the nuclear
train can be satisfied by varying the place in orbit at the time of the
1992 encounter and considering the subsequent differential perturbations.
Using the above orbital elements, the undersigned notes that the train as
reported on IAUC 5730 corresponds to a variation of +/- 1.2 seconds.
Separation can be regarded as an impulse along the orbit at that time,
although the velocity of separation (or the variation along the orbit)
depends strongly on the actual value of Delta_J.  At the large
heliocentric distances involved any differential nongravitational
acceleration must be very small, as Z. Sekanina, Jet Propulsion
Laboratory, has also noted.  Extrapolation to shortly before the 1994
encounter indicates that the train will then be about 20' long and
oriented in p.a. 61-241 deg, whereas during the days before encounter the
center of the train will be approaching Jupiter from p.a. about 238 deg.

1993 May 22                    (5800)              Brian G. Marsden

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