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Re: (meteorobs) Comet Tabur Meteors?
Not to burst anybody's bubble, but the meteors seen while observing comet
Tabur were not related to this comet. This is a clear case of a
coincidence. The radiant of a comet's meteor activity is basically the
point where the comet's orbit intersects Earth's atmosphere. This
intersection point is also known as the tangent. (This is the simple way of
discussing this, the mathematics are much more intricate and too long for
this letter.)
As Enrico Stomeo computed on September 20, and as I have since confirmed,
the point of closest approach between the orbits of Earth and comet Tabur
occurs on October 24. The intersection point mentioned above will cause the
stream's radiant to be centered at RA=63 deg, DEC=+73.4 deg or in
Camelopardalis, near the Cassiopeia border.
I was preparing something for this radiant, but this is a good time to
express enough of the scant details to encourage observations over the
period of October 20 to 28.
Sincerely,
Gary W. Kronk
A Possible Temporary Minor Radiant for Comet Tabur?
Under normal circumstances, meteor activity from a long-period comet such
as Tabur, where the closest approach between the comet's orbit and Earth's
orbit is 0.11 AU, would be extremely unlikely. So why should a search be
encouraged? The reason is simple: comet Tabur and 1988's comet Liller were
probably part of the same comet and split comets can offer some interesting
possibilities.
Liller's original orbit was around 2900 years (Tabur's orbit is not yet
precise enough to determine its original orbit) and, according to Brian G.
Marsden, it is probable that these two comets separated near the last
perihelion passage.
There are different types of comet splits. The most common type is when a
temporary companion is produced. This companion is probably a large piece
of the comet's crust and these generally appear prior to a comet's
perihelion passage--usually between one and two AU from the sun--when a
comet's activity is really starting to kick in. As stated these companions
are temporary. They generally do not last more than a few days, depending
on the distance from the sun. The cohesive ice rapidly melts and the
remaining dust cloud will be dispersed. The Tabur and Liller comets are
apparently in the class of least common comet splits: those involving a
significate splitting of the original comet's rocky nucleus. These comets
are generally more permanent and can separately endure for many revolutions
around the sun.
All comet splits seem to have one thing in common: they seem to be
accompanied by an outburst in brightness. The outbursts are the result of a
massive release of dust. If you pick up a clod of dirt and break it in two
you might have a piece in each hand, but many smaller pieces will fall to
the ground, lie in your hand, and sit on the two individual pieces. Without
gravity the separation of these two pieces would leave a trail of debris
between them.
It is my belief that a weak debris cloud probably extends between Liller
and Tabur. I refer to this as "weak" because if you take the distance
between the two comets (Liller is currently 23 AU from the sun), assume a
height and width of 0.05 AU (some comets produce a larger torus, but this
is generally not true for long-period comets), assume the particles are
evenly distributed throughout the torus, and assume that the Earth plows
right through the middle of the stream (this does not happen, by the way),
it would require some serious tonnage to allow hourly rates of one per
hour. In fact, based on some estimates of the mass of cometary nuclei, the
mass of the particles between the two comets might exceed that of at least
one of the comets.
Have any observations of this meteor radiant ever been made? The answer
seems to be an emphatic no. Historically, there is absolutely no trace of
this radiant in the records of the AMS and I can find no trace among
photographic meteors. It also seems that the radiant was never detected by
Herschel and King. There are a couple of near misses among the nearly 40
thousand radio meteors collected during the Harvard Radio Meteor Project,
but these have distinctly short-period orbits and are very likely not
related. Denning has a couple of close radiants, but they are based on a
few meteors plotted during a period of a week or more. Since the radiant
would drift by several degrees during the periods covered, I accept these
radiants only as chance alignments.
The next obvious question is, Have any meteors from this debris cloud been
detected during the last eight years (the time between Liller and Tabur)? A
request was made by myself a few weeks ago, but George Zay has been the
only person to respond. His observations only involved plots in 1994 and
1995, but no meteors from the Camelopardalis region were noted. It would be
valuable if other plotting observers would check their records during the
last eight years.
So, once again, why do a search for meteors from this comet? The stream's
core would be farther than normal from the orbit of Earth and the likely
debris cloud would be weak because of its being strung out so far along the
orbit. The answer is basically curiosity. Something that all meteor
observers should appreciate. We do not know the circumstances of the
splitting or the accompanying outburst, so surprises could exist.
October 24 would be the key date for observations and it might be the only
possible date to see activity. But I would like to suggest observations
beginning four days before and ending four days after this possible date of
"maximum". Therefore, for this minor meteor shower watch, observations,
especially plotting, should be conducting on as many days as possible
during the period of October 20 to 28. As usual, all reports should still
be sent to Mark Davis.