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(meteorobs) (PHA's) & question?
Hi Jerry, (Jerry Armstrong)
Fantastic post on asteroid threat (PHA's) and I learn much about the comet
threat also. On the Jim Scotti stats I have a few questions but no doubt
of it's accuracy. An asteroid about 200 meters passes between Earth and
moon every 24 hours is possible from Scotti's calculations.
I was wondering if he meant that a 200 meter rock passes that close to
Earth's orbit every 24 hours or that physically a rock that size is coming
that close to earth every 24 hours? Perhaps that's a question I should
direct to Jim himself but feel free to answer if you know.
Recently I looks at some reports on the Dr. Jack Hill's abstract on Jan
8th, 1998 before the American Astronomical Society, which seems to say
asteroid of 200 meters or less with few exception (Iron asteroids) will
result in air burst and only local damage. If so does this rule out impacts
with the ocean causing tidal waves?
(For thoses on the list who do not know Jack Hill is a geophysicist at Los
Alamos Nat Labs in New Mexico, USA - see David Morrison's NEO New of
1/9/98 or go to http://www.phoenixat.com/~vnn2/morrison.htm )
Victor
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> From: Jerry Armstrong <jacomet@atl.mindspring.com>
> To: meteorite-list@meteoritecentral.com
> Subject: Re: potentially hazardous objects (PHA's)
> Date: Saturday, February 21, 1998 11:34 AM
>
> At 07:14 AM 2/21/98 -0700, you wrote:
>
> >Second, in you posting, you provide several reasons for a reduction in
time
> >for both predicting if an asteroid will intersect the earth in orbit
(how's
> >that for depersonalizing the issue), and in knowing the energy and
location
> >of the impact. While this information would be interesting in an
> >existential sense, is it really important. In other words, what
> >would/should/could we do with this information?
>
> I vaguely remember reading something somewhere, that if an
impact
> were to occur that the heads of state and most notably the IRS would
be
> evacuated to a safer location, then let nature take it's course. But,
don't
> quote me on that, although that would in all likelyhood be the way
that
> not only ours but most governments would probably handle the
> situation. This being of course if the impact were going to occur
without
> sufficient warning to evacuate the populace, or if say an impact
had
> occurred in the middle of the ocean. I have seen the panic when a
hurricane
> comes ashore and the evacuation is usually OK but somewhat confused, now
> just image a wave that will reach several tens of miles inland and with
> little or no warning.
> >
> >How do we apply a time frame to an impending impact. What is knowing
about
> >the impact early or late relative to? Is there a plan to deal with the
> >impact?
>
> I believe these questions were answered above.
>
> To prevent the impact? Is a certain amount of advanced warning
> >needed for something in particular?
>
> These are just my thoughts on this. Comets are perhaps the
worst
> ones to deal with. They are outgassing and this produces a jetting
effect
> which makes their path unpredictable. Now we can predict with some
> ammount of certainty the location of a comet for a telescope, but even
> here we encounter some discrepancies. And the coma of a comet is BIG,
> something thatmost amateur astronomers fail to realize. Given this a
comet
> say like Hale-Bopp is a typical fuzzball when first discovered. But,
you
> have to put this into perspective, that tiny fuzz ball when seen up
close
> is very very large. In the order of tens of thousands of miles in
diameter.
> That is why the slight shift in position is not that noticable. But,
when
> it gets say within one or two million miles of the Earth, the emmense
size
> becomes very apparent. Hale-Bopp was never closer than 30 odd million
miles
> at best, Hyakutake came as close as a little over 9 million miles.
And
> by the way, if you imagine a sphere of just 0.1 Astronomical Unit, or
9
> million miles, there have been 14 comets to venture inside this zone in
> recorded history. And Hyakutake doesn't even make the LIST!!!!
> My point is, that we would not have time to determine if the
> nucleus would impact with the Earth until just a few short weeks at
most.
> Now, most of the talk is centered on an asteroid collision. Of
> these asteroids, basically only (433) Eros is large enough to cause
global
> extinction. The rest are in the 5 kilometer or less size range.The IRAS
> satellite when it was in service discovered many,many objects and
should
> have detected any of the Earth Approach Objects out there in the (433)
> Eros size range. And I stress, should have, we can't be 100% sure nor
will
> we ever be. So in effect, if an impact does occur, it will most
likely
> be from one of the lesser varieties. Even an asteroid that is twice the
> size of a football field would certainly wreck havoc on the area it
> strikes, and an ocean impact would be far worse. !996JA that passed as
> close to us and the moon was just such a size range. Jim Scotti once
> told me that given the amount of area in the sky that he patrols with
> Spacewatch and the number of objects such as 1996JA that he and his
> colleagues have discovered, there should be by calculation a 200 meter
> diameter object passing between us and the moon every twenty four
> hours. That's scary, but I don't plan on loosing any sleep over it
unless
> I plan on looking at it through a telescope.
> Now, getting back to comets, they pose a slightly different
problem.
> Being as I explained earlier that it would be difficult if not
impossible
> to predict an impact until just a few weeks prior, they DO have the
> capability of global extinction. Comet Hyakutake 's nucleus was only 2
> kilometers diameter so it did not, but Hale-Bopp had a nucleus
> calculated at 75 kilometers diameter. And remeber the list I told you
about
> with the 14 comets whizzing by at less than 0.1 AU? Well guess what,
good
> old faithfull Halley's Comet makes this list THREE times, and it's
nucleus
> is about 10 kilometers. I'm not saying that Halley's will ever impact,
but
> there is one comet that is in the Halley class that is destined to
either
> hitting the Earth or being ejected from the solar system due to a very
close
> encounter with the Earth. This is our old friend P'Swift-Tuttle. It
should
> make a grande spectacle in about 130 years when it makes it's next
> return. Although there was some aprehension atone time a few years back
> when it was recovered that calculations revealed it had a 1 in 400
> chance of hitting theEarthon it's next return in 2130 AD. But after
all
> the observations were in, it was soon found not to be the case. It
will
> however have it's orbit shifted ever so slightly that any future
> predictions become hopeless,and this is where the uncertainty lies as
to
> when the event will take place.
> I could ramble on for hours discussing asteroids and comets so
I
> had better stop here, I hope this helps.
>
> Jerry
>
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> | jacomet@mindspring.com |
> | 8526 Moccasin Lake Drive |
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>
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Victor Noto - Kissimmee, Florida USA
vnn2@phoenixat.com
http://www.phoenixat.com/~vnn2/BIGROCK.htm
Website theme quote:
"Life really is a Rock and
the Big Rock giveth and taketh away all life!!"
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