Searching for pre-breakup images of the split comet D/Shoemaker-Levy 9 from Kiso Schmidt plates

We searched for images of D/Shoemaker-Levy 9 (SL9) before breakup from the 58 Kiso Schmidt plates covering November 1986 to March 1992, which were initially taken for the orbital improvements of the jovian outer satellites. The breakup of SL9 into a chain of ≈20 fragments is believed to have been due to tidal forces during an extremely close approach to Jupiter in July 1992. We made an extensive search of moving objects near the areas predicted from the errors in the adopted orbital elements of SL9 and detected four possible “candidates” of SL9 before breakup. We applied orbital determination methods for one object and compared motions with SL9ʹs predictions for the other three objects. We could not obtain orbits which are consistent with the likely SL9 orbits. This leads us to conclude that an upper limit diameter of prebreakup SL9 is 24–37 km, which is consistent with the diameters estimated by other investigators.