So far as I know, it is now classified as a Long-Period Comet. Its orbital period is measured in thousands of years. It has an ellipticity that suggests it is not in a parabolic or hyperbolic orbit, so it probably is periodic.
According to Don Yeomans at NASA JPL (April 10, 1997 calculations)
By integrating the above orbit forward and backward in time until the comet leaves the planetary system and then referring the osculating orbital elements to the solar system barycenter, the following orbital periods result: Original orbital period before entering planetary system = 4206 years Future orbital period after exiting planetary system = 2380 years The difference between the inbound and outbound orbital periods is due primarily to an approach to Jupiter (0.77 AU) in April 1996
According to Brian Marsden, based on a report at a 1998 international conference in Tenerif on Hale-Bopp:
Based on more than 2600 astrometric observations from 1993-98, Brian Marsden has calculated a new and improved orbit, now taking into account non-gravitational forces arising from the jet effect associated with the Comet's vigorous activity. He found that the original period was 4211 years and that the future period will be 2392 years with a formal uncertainty of a few months only. However, the limited knowledge about the future development of the Comet's activity may still change this period somewhat. Had it arrived about four months earlier this time, it would have passed the Earth nearly as close as did Comet Hyakutake one year earlier. In that case it would have been an incredible view. Interestingly, it appears that Comet Hale-Bopp may have passed very close to Jupiter on June 7, 2216 BC. In view of the rather unstable orbit, it is unlikely that there have been more than a few earlier, close perihelion passages.
The most recent image of Comet Hale-Bopp (above) was obtained at ESO on June 18, 1999, with the SUSI2 instrument at the ESO 3.5-m New Technology Telescope (NTT) at La Silla. This observation was somewhat difficult, as the comet was very low in the sky at the beginning of the twilight. At that time, Comet Hale-Bopp was located in the southern constellation Dorado (The Goldfish).
It was about 1295 million km (8.66 AU) distant from both the Earth and the Sun, i.e. at about as far away as planet Saturn.
Copyright 1997 Dr. Sten Odenwald
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