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(meteorobs) MNRAS



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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