🚀 go-pugleaf

In article <2635@ssc-vax.UUCP> eder@ssc-vax.UUCP (Dani Eder) writes:
>
>If an asteroid misses the Earth by 500,000 km, that is about 80 Earth
>radii.  Let us comapre this to more familiar events and see how this
>compares.  The mean radius of a car is about 2 meters.  80 times 2
>meters is 160 meters (525 feet.).  If a car crosses a 4 way intersection
>while you are that far away, do you call it a near miss? I think not.
>The collision cross section of an irplane is 20 meters in the horizontal
>radius and 4 meters in the vertical direction.  A crossing at 1600
>meters horizontal separation (1 mile) is hardly a near hit, as is
>320 meters (1000 feet) in the vertical direction.
>

Carried to an absurd length(reducio ad absurtum(sd?)), let's assume
that instead of a another car crossing an intersection a couple of
blocks away, a 747 crashes. Or an atomic bomb goes off? (Phewww! just
missed me (:-).

Please note in the following re-post:

"His[ Eugene Shoemaker, a respected US Geological Survey scientist]
calculations suggest that asteroids packing the explosive energy of one
megaton should enter the atmosphere on an average of once every 30 years,
larger asteroids with a 20-megaton punch every 400 years, and a 1 km, 10,000
megaton comet or asteroid once in 100,000 years."

Maybe we should consider a cheap form of insurance, like a radar satellite
or two pointing out instead of in(of course the shuttle would carry them right)?

Note the Siberian comet/asteroid was estimated at 12-megaton, about 80 years 
ago(so we have 320 years {:->).

[3 screen article follows]
From decwrl!ucbvax!hplabs!hp-pcd!hpcvlx!gvg Tue May  2 10:05:21 PDT 1989

Article 11311 of sci.space:
Path: sun!decwrl!ucbvax!hplabs!hp-pcd!hpcvlx!gvg
>From: gvg@hpcvlx.HP.COM (Greg Goebel)
Newsgroups: sci.space
Subject: Re: Re: Asteroid Encounter
Message-ID: <101270016@hpcvlx.HP.COM>
Date: 1 May 89 15:21:48 GMT
References: <101270015@hpcvlx.HP.COM>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 93

Dealing With Threats From Space

   Michael Lemonick

   TIME / 9 JUN 86 / P 65

   It is a sunny afternoon in Karachi, and streets of Pakistan's largest
   city are crowded with shoppers, apparently unconcerned about the rising
   tension between Pakistan and India.  Suddenly a second sun bursts into
   view overhead, so bright it temporarily blinds thousands and so hot it
   blisters the skin.  Thirty seconds later, the shock wave hits, 
   crumbling buildings and throwing people to the ground.  To the 
   Pakistanis, only one explanation is possible for the tremendous blast:
   India has launched a nuclear attack.  They immediately order their bombers,
   armed with atomic bombs, to strike back at India, which responds in kind.
   Only later do the surviving officials learn of their mistake.  The 
   object that exploded over Karachi was not a nuclear weapon but a large
   meteor hurtling in from outer space.

Though this sounds like the plot for a TV movie, Eugene Shoemaker, a respected
US Geological Survey scientist, is concerned that just such an event -- and an
unwarranted reaction -- could occur.  Shoemaker expressed his fears at a 
Baltimore meeting of the American Geophysical Union (AGU):  "The effect of a
meteor blast appears the same as a high-altitude nuclear explosion," he said.
"If this happens in the wrong place, people will think they've been nuked."

Meteors, which are asteroids or cometary debris that has entered the
atmosphere, continually shower the Earth.  Most of them are small and either
break up or are burned to ash by friction.  But, explains Shoemaker, the
incineration of larger asteroids is far more violent.  As asteroid 80 feet
across, striking the atmosphere at 50,000 MPH, compresses the air in its path
so much that in effect the asteroid is stopped dead in its path, converting
kinetic energy almost instantaneously into heat, light, and a powerful shock
wave.  That causes a tremendous explosion, in this case equivalent to a
one-megaton bomb.

If a meteor were to burst in the atmosphere tomorrow, Shoemaker says, "the
Soviets and the US would know what it was" and not react militarily.  Their
detectors could distinguish between a nuclear explosion -- which generates
million-degree temperatures, X-rays, and gamma rays -- and an exploding meteor
-- which would produce considerably lower temperatures and no deadly radiation.
But smaller nations, unaware of the nature of the blast, might react violently.
Says Shoemaker:  "Suppose it happens over Syria or Pakistan?"  He proposes that
the US immediately try to determine whether the explosion was of cosmic origin
and notify the affected nation.

Since 1973, Shoemaker has been photographing the sky in search of asteroids
that periodically cross the Earth's orbit and thus pose a danger of collision.
To date, he says, 57 such asteroids at least 1 km in diameter have been
catalogued.  In addition, about three Earth-crossing comets are detected each
year.  From the rate at which new Earth-crossers are detected, Shoemaker
estimates that there are some 2,000 asteroids in this category and that 100
comets intersect the Earth's orbit every year.

His calculations suggest that asteroids packing the explosive energy of one
megaton should enter the atmosphere on an average of once every 30 years,
larger asteroids with a 20-megaton punch every 400 years, and a 1 km, 10,000
megaton comet or asteroid once in 100,000 years.

This century has already seen a major meteorite blast.  In 1908, either an
asteroid or comet exploded about five miles above the remote Stony Tunguska
River region of Siberia, igniting and flattening trees over hundreds of square
miles.  From descriptions of the blast and photographs of the damage,
scientists have estimated that the object was at least 200 feet across and
caused a 12-megaton explosion.

Depending on their velocity, size, and composition, some meteors survive the
fiery trip through the atmosphere at hit the ground, at which point they are
called meteorites.  Most are in the form of pebbles or small rocks, but
occasionally they are much larger.  Scientists think it was a 130-foot chunk of
meteoric iron that hit Arizona with a force of 15 megatons between 20,000 and
50,000 years ago, digging a crater three-quarters of a mile across and 600 feet
deep.

But even greater menace lurks in the darkness of space.  Scientists have
speculated that objects as large as several miles across have crashed into the
Earth, spewing millions of tons of debris into the atmosphere, blotting out the
Sun for months or years, and causing mass extinctions of life -- including,
many believe, the dinosaurs.  Of the known larger Earth-crossers, none seem to
pose a threat in the near future.  But, says Shoemaker, "until we have tracked
all of them, something could sneak up on us."

What if a large asteroid or comet is discovered heading for the Earth?  At the
AGU meeting, Shoemaker and colleage Alan Harris, of the Jet Propulsion
Laboratory in Pasadena, California, suggested that the intruder could be
diverted by landing a thrusting device on it.  As a last-ditch effort, a small
nuclear warhead could be detonated on or near it.  Says Shoemaker:  "We have
the technology to do that right now."  But if the explosion simply broke the
meteorite into large chunks, the danger would only be multiplied.  "The more
prudent solution," says Harris, "is to burrow a substantial charge into the
object and blow it to smithereens."

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# mike (sun!mae), M/S 8-04
"I'd rather sniff French shit for 5 years then eat
Chinese shit the rest of my life"  -Ho Chi Minh-