COMET 1999 J3 (LINEAR) and the GAMMA URSAE MAJORIDS
Prospects by Reinder Bouma
This comet was one of several faint comets discovered by the LINEAR program in May 1999. At discovery it was an inconspicu- ous object of 17th magnitude, but when a first orbit became available, it was soon realized that this comet could become an interesting object both for visual comet observers, AND meteor observers. A preliminary orbit indicated that periheli- on was due on September 20, only 0.98 AU from the Sun. Moreover, it appeared that the descending node of the high inclination orbit was only 0.01-0.02 AU outside the Earth's orbit, suggesting that dust particles associated with this comet could possibly be observed around 11 November as fast meteors emanating from a point near Gamma Ursae Majoris. Now that the comet has been observed for almost 5 month, and a fairly accurate orbit has been published, it is possible to give a better assessment of what to expect of the associated meteors.
Visual observations of this comet since discovery show that this is an intrinsically faint comet, with Ho ~ 9. The very steep rise in brightness with n = 6-8 ('normal' is 3- 4) strongly suggests that this is not a dynamically new comet, but rather an old one, that is only active during a short period around perihelion passage. Although a short (gas)tail developed, it is also clear that this comet is not producing a lot of dust. Nevertheless, it was a nice object in the morning sky, reaching magnitude 7.5-8 in the middle of October. Currently it is moving to high southern declination and star- ting to fade.
The most recent orbital elements published in MPC 35814 also show that C/1999 J3 is not a 'new' comet; the indicated period is ~63000 year. It should be noted though that this figure is only a rough indication. Strictly speaking the period is only valid for a choosen time close to perihelion, and planetary perturbations may have influenced this figure considerably, sothat the 'original' period could easily be a few ten thou- sends years more, or less. But it now appears safe to assume that this comet has passed the inner parts of the solar system before, although the period is quite long.
The aforementioned orbital elements show that comet 1999 J3 passed its descending node on October 2.86 (UT), at 1.0013 AU from the Sun, only 0.0115 AU outside the Earth's orbit. The Earth itself is crossing the orbital plane on November 11.82 (UT), 40 days 'behind' the comet. This is also the best time that associated meteors can be observed, with a radiant near R.A. 176 deg and Dec. +54 deg. (J2000.0). This position is very close to second magnitude Gamma Ursae Majoris.
This sort of observing geometry has generally been found the best for observing (high) activity of any possible shower. Unfortunately, at the time around orbital plane crossing the radiant is due north for European observers, and consequently low over the horizon, but the further east one goes through (Northern) Europe and Asia the better. Possible meteors are swift, much like the Perseids.
Remains the important question what sort of activity we can most likely expect in this particular case...
I don't think that here any comparison with most known meteor showers is appropriate, even the ones that have similar dis- tances to the Earth's orbit and a faint parent comet, like P/Giacobini-Zinner/Draconids and P/Tempel-Tuttle/Leonids, because of the big difference in time scale. One may expect that any dust that has been ejected during a previous perihe- lion passage of C/1999 J3 has been largely dissipated after several tens of thousends of years, even when planetary per- turbations are very minor, because of the high inclination long period orbit, and thus not complicating the matter as in the case of showers that are mainly residing in the inner solar system, and more or less permanently subject to planeta- ry perturbations, particularly by Jupiter.
But some (heavy) particles may have survived in the wake of the comet, and some of these we may encounter...
It should be noted further that no long period comet in an orbit that comes very close to the Earth has ever produced a major shower. A good example is C/IRAS-Araki-Alcock that came very close to the Earth in May 1983; the Earth passed the plane of the comet near the descending node only 2 days BEFORE the comet, and nothing significant was seen then. However, careful monitoring by Dutch observers Langbroek and Miskotte , as well as some other observers, in subsequent years, showed a low annual activity of associated Eta Lyrids, with a ZHR of ~2. This comet has an absolute brightness simi- lar to C/1999 J3 with H10 ~ 9, but its period is considerably shorter, near 1000 years.
Even a big comet like 1995 O1 (Hale-Bopp) that released huge amounts of dust, only produced a few possible meteors in early January 1998, although admittedly its miss distance is 10 times larger than that of C/1999 J3.
Considering all the pro's and con's I find it unlikely that C/1999 J3 will produce a significant shower this year, despite the favourable geometry. Nevertheless, it may be useful to be on the alert, particularly within 24 hours on both sides of the orbital plane passage, for fast meteors coming from the Big Dipper. In would not be the first time that meteor showers have a surprise for us after all!
Reinder J. Bouma
phone: +31 (0)50-5418227
email: email@example.com or
Linearids, November 11
RA = 11h40m ; DC = 53
Utrecht, the Netherlands
52 N ; 5 E
Time Azimuth Elevation [UT] (N = 0) 16 325 26 17 333 22 18 342 18 19 351 16 20 0 15 21 10 16 22 19 18 23 28 22 0 36 27
|This page was last modified on October 25, 1999 by
Reinder Bouma, Casper ter Kuile and Hans Betlem