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Re: Close-Call Asteroid Coming: Info. on Impact Scenerio
Michael & List ~
I realize that this question was addressed to Ron Baalke, but its
Saturday and everyone deserves a day off. :-)
Perhaps this answer that I'd sent to Gene would be helpful.
As sent to Gene Fri. May 28:
This gives a fairly concise description of the effects of a 1 Km.
impact. Tunguska was significantly smaller, and exploded well above the
surface. For additional data (most of it VERY good), enter
<http://www.ask.com> and enter the question: "What would be the effect
of a 1 km. meteor impact on Earth?" Some great info., and excellent
simulations from Scandia & JPL.
....................................................................................
(From <http://www/faqs.org/faqs/astronomy/faq/part5/section-25.html>)
Author: Joseph Lazio
The Earth is constantly pelted by bits of cosmic debris. Most of this
simply burns up in the atmosphere (as one can attest by simply
watching meteors on a dark night). However, if an object is big
enough it can survive passage through the atmosphere. The damage done
by a meteorite (an object that strikes the Earth) depends upon its
initial size.
10--100 m: Objects in this size range can produce devastation similar
to that of an atomic blast (leading to them occasionally being called
"city-busters"). Effects include severe damage to or collapse of
standing buildings and the ignition of flammable materials leading to
widespread fires. The radius over which such effects occur would vary
depending upon the size and composition of the object, but could
easily exceed 10 km. The Tunguska event, in Siberia, of 1908 is
thought to have been from an object about 60 m in size; it led to
trees being flattened out to 20 km and trees 40 km away being damaged.
At the small end of this size range, objects about 10 m strike the
Earth about once a decade. Fortunately, only the densest objects,
those containing iron, survive to the surface; most of the objects of
this size explode sufficiently high in the atmosphere that there are
no effects (other than maybe a loud noise) on the ground. At the
larger end of this size range, it is estimated that the Earth is
struck several times a millennium or about 1 impact every 100--200 yr.
100 m--1 km: Objects in this size range are likely to cause severe
damage over a regional area, possibly as large as a continent (hence
the name "continent-busters"). If they strike land, they will almost
certainly produce a crater, while an ocean impact will generate large
tidal waves. A 150 m object might produce a crater 3 km in diameter,
an ejecta blanket 10 km in diameter, and a zone of destruction
extending much farther out. For a 1 km impactor the zone of
destruction might reasonably extend to cover countries. The death
toll could be in the tens to hundreds of millions. A 1 km impactor
could begin to have minor global consequences, including global
cooling caused by vast amounts of dust in the atmosphere.
Estimates from the geologic record suggest that craters are formed on
the Earth roughly once every 5000 yr.
1--10 km: Objects in this size range are likely to cause severe global
effects ("species-busters"). An impact 65 million years ago by an
object of 5--10 km in diameter is thought to have been partially or
fully responsible for the extinction of half the living species of
animals and plants at the time, including the dinosaurs. The crater
alone from such an impact will be 10--15 times larger than the object
itself. World-wide crop failures from dust injected into the
atmosphere could imperil civilization, and the largest-sized objects
could make the human species extinct.
The frequency with which the Earth is struck by such objects has to be
estimated from the geological and paleontological record. At the low
end of this size range, estimates are that such impacts occur roughly
every 300 000 yr; at the upper end of the size range, impacts occur
about every 10 million years.
...............................................................................................................................
Of course, the BEST place to be if you're in the path of a large speeding rock is
elsewhere ... sure be a good time to work on the privatization of space, huh? But
much more is being done now (by government and private sector) to identify and plan
countermeasures for this sort of thing, so its not time to panic or cash in your
retirement benefits just yet.
Peri Craig
=====================================
Michael Blood wrote:
> >This would be like another Tunguska, wouldn't it?
> ---
> No, 1999 AN10 is in the PHA category and about 1 km in diameter. It
> would do major damage if it hit the Earth.
> Ron Baalke
> ---
> Ron,
> I am confused. You do NOT consider Tunguska "major damage?"
> The 65 MYA dynosaur exterminator (as well as about 65 to 75% of all
> life on earth) was extimated to be 6 km in diameter.
> However, 1 km has "only" a very small fraction of the mass of a 6 km
> body.
> Personally, I consider Tunguska to have caused ultra major damage (what
> was it? Flattened 10,000 square miles?) - however, it was in a nearly
> unpopulated area - it certainly would have entirely obliterated any
> major city on earth. However, relative to a 6 km diameter body, 1 km is
> "relatively" "small." "Major," yes, but still significantly less so than
> the impact of the 65myo Yucatan impact. So, what IS the estimated
> impact ?
> Best wishes, Michael
>
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