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Re: (meteorobs) NASA News articles
There is one general point in the piece "Leonids on the Horizon" that has
been repeated so often it has been assumed to be true.
>Scientists have learned that if the Earth crosses the orbit of
>Temple-Tuttle too soon after the comet's passage, then there is no storm,
>just a strong shower. Apparently that's what happened in 1998. In
>recent history no Leonid storm has ever occured less than 300 days after
>Tempel-Tuttle passed by Earth's orbit.
The reason there has been no storm under such conditions in the last 200
years is because the situation has never occurred in the last 200 years
where the Earth was close to either the comet or dust trail orbits.
As the dust trail theory is the only one that successfully fits the times
and intensities of storms, one could consider what it implies for storms
should the Earth pass just behind the comet.
The dust from that (pre-) perihelion passage would occupy only a short
segment of the orbit in the vicinity of the comet, but would be more
concentrated than the most dense storms encountered in the last 200 years.
This region will also contain a (much wider) spread of meteoroid filaments
within the resonance zone that would overall be much stronger than the
1998 activity, due to the larger number of such filaments close to the
comet. Old dust trails will become "detached" (or at least depleated)
around the resonance boundary, whereas the young dust trails will be more
or less uniform.
Outside this resonance zone, would be the "trailing" dust trails. The
densest parts of these, in terms of visual meteors, does indeed lag the
comet by roughly 6 months per orbit. However, encounter with the densest
part of these trails closer in to the comet would still produce an
impressive storm. The closer one gets to the comet, the closer the dust
trails are to each other, so one would expect multiple encounters with
dust trails in this region. These trails will necessarily be located
close to the comet's orbit and the "target area" the Earth must pass
through is thus small.
The dust trail theory predicts that storms occur when the Earth encounters
a dust trail that has "strayed" well inside the Moon's orbit. The
circumstances from year to year are hit or miss, especially the further
one goes from the comet. These distant dust trails are widely spread by
differential perturbations, thus further from the comet the target area is
much larger, but the earth will most years miss the trails. The 1869,
and 1969 outbursts are examples of this, as is the predicted outburst in
2006.
I would suspect that the biggest storms will occur within this supposed
exclusion zone, but the size of the target area is small, and thus would
be rarely encountered.
Cheers, Rob
Robert H. McNaught
rmn@aaocbn.aaodot gov.au
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