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RE: (meteorobs) MNRAS
Hi,
I give a few points to consider and to take into account in this
question. I have read the MNRAS1977 results earlier, but don't have the
paper now by me.
In my opinion Uranus may and will have its share on the spread of the
particles as told in the paper, but only for some part. I expect that
the situation would be almost the same without that "Uranus effect".
One can think that the meteoroids have had time to spread in the whole
orbit. Looking figures with the trails plotted some years after the
parent comet, the trails tend to spread into a wider space region as the
time from the comet location increases. So an encouter with a trail far
away from the comet is less probable. Further, if an encounter howewer
were to happen, either the trail is quite old, or the original delta-a
high, meaning less visible size meteors in an encounter. However it (the
total swarm from different trails) is practically never (or soon enough
to still have the change to get in the vicinity of an active parent)
very well mixed.
(There may be the possibibity to see meteors in 2003 that are from a
known release (15 comet revolutions) and that lag the parent comet more
than one orbit (that were trapped in the 1/3 resonance with Jupiter).)
Actually (although this may seem counter intuitive) in a longer period
(parent comet and also meteoroids) orbit it will take less revolutions
for the particles to spread along the orbit. Then with the smaller
number of revolutions the mixing will be more uniform in the whole
orbit. Considering a long period orbit like the Lyrids or Aurigids (and
alpha monocerotids, although this without known parent comet) quit a
good mixing in the whole orbit will not require many revolutions. The
mixing after one revolution can be considered to form of multiple loops
that appear to go 'back and forth' that look almost random (even in
2-rev. in a 1000 year orbit) in a plot, with not extremely densely
model.
In contrast, with short period orbits the spread will take so many
orbital revolutions, that at the 'end head' (ie. far from the comet) the
spread of different trails from each other is very big as compared to
meteoroids from a few orbits ago and more near the parent comet (and
also those that are old but in the same synchronzation as the parent).
But the totality is still not well mixed. It may be that with a
relatively short period orbit an unique background will never be
reached, as long as the comet still passes close to the Earth orbit and
keeps active. Actually any such comet, most probably, doesn't pass close
to the Earth orbit for a very big number of revolutions.
The spread behaviour of Perseids is somewhere between the Leonids and
the truly long period showers but the situation now may more resemble
the long period cases.
I hope that this gives some further clarification on this question.
Besides the Leonids (and Ursids and Perseids, unfortunately not
Giagobinids, because of lack of time), the study of the long period
outburst (Lyrids, Aurigids AMO's etc) has been one of my main studies
for about three years now. We have, with Peter Jenniskens, a paper on
these accepted for publication in ICARUS.
Esko
>>>
Daniel,
Could you give those of us who are anacronymically challenged, which
journal MNRAS is, so we could try to find a copy of that article?
Thanks,
Kim Youmans
----- Original Message -----
From: <leoniden@hetnetdot nl>
To: <meteorobs@atmob.org>
Cc: <tux@campioni.dyndns.org>
Sent: Tuesday, November 26, 2002 4:23 AM
Subject: RE: (meteorobs) Chances of another meteor storm?
> I'm also wondering why there is this 33 year period. I mean, the dust
> trails (ejected 1799, 1833, ... of course every 33th year, that's
> clear) will remain on their position (more or
> less) and to me it seems like earth is going to pass through them same
> likely every year.
One important thing to keep in mind is that the dust is not just sitting
there out in space. The particles released by the comet are moving along
with it at nearly the same speed (70km/s). Slight variations in the
speed cause the dust particles to spread out across to whole cometary
orbit over many years. This causes the annual activity each time Earth
crosses this orbit.
Somehow, the dust has remained in dense, compact trails in a small
window around the comet while in other parts of the orbit the trails
have been disturbed. Only when earth crosses a trail in the unpertubed
window, a meteorstorm can be expected.
I.P. Williams gives a possible explanation in his article: "The Leonid
meteorshower: why are there storms, but no regular annual activity?"
(MNRAS1997).
The Leonid are moving very fast when they are close to Earth, they then
return into the solar system and slow down. At some point almost all
speed is lost (to about 2km/s) and the particles return towards the sun.
Williams noticed that the point where they return is very close to the
orbit of Uranus. He then looked at the orbital periods of the Leonids
(33 years) and Uranus (84 years). It seemed that large parts of the
Leonid orbit came under the influence of Uranus. In these parts the
trails are messed up, but there also was a small section of the orbit
which wasn't influenced.
Coincidentially this is exactly the section of the orbit where the comet
is and so the trails remain compact around the comet. In 2160 the
section will be pertubed and the orbit of Tempel-Tuttle will change,
probably ending the Leonids completely.
I haven't been able to find any comments, critism, additions or
follow-ups to this article so I don't know what the current status of
this theory is. To me it sounds reasonable.
Yours,
Daniel
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