mae@vygr.Sun.COM (Mike Ekberg, Sun {GPD-LEGO}) (05/05/89)
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." [<>] # 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-
kgd@inf.rl.ac.uk (Keith Dancey) (05/12/89)
In article <103026@sun.Eng.Sun.COM> mae@sun.UUCP (Mike Ekberg, Sun {GPD-LEGO}) writes: > >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." > My understanding is that the demise of the dinosaurs extended over a period of order of magnitude of a thousand years. Certainly long enough to place doubt upon the viability of a single catastrophy such as the one mentioned. If the palaeontological evidence is not contradicted (and I have understood it correctly) then a *series* of such catastrophic strikes would be required. That is not say a single catastrophy is ruled out, but it looks as though its effects must be longer-lived than a few years. As for tracking "all" large, earth-crossing asteriods, there is a danger of conveying the unspoken idea that the number may be fixed and finite for all time. I think such a concept is also under question. There is just the possibility that these bodies are disturbed out of an otherwise harmless state by the dynamics of the galaxy. This means their numbers may be added to at any time unexpectedly. -- Keith Dancey, UUCP: ..!mcvax!ukc!rlinf!kgd Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, England OX11 0QX Tel: (0235) 21900 ext 6756 JANET: K.DANCEY@uk.ac.rl.inf
eugene@eos.UUCP (Eugene Miya) (05/14/89)
If you are really interested in this. I recommend the work and writings of
Preston Cloud.
Longish signature follows "Type 'n' now"
Another gross generalization from
--eugene miya, NASA Ames Research Center, eugene@aurora.arc.nasa.gov
resident cynic at the Rock of Ages Home for Retired Hackers:
"You trust the `reply' command with all those different mailers out there?"
"If my mail does not reach you, please accept my apology."
{ncar,decwrl,hplabs,uunet}!ames!eugene
Live free or die.hazel@unm-la.UUCP (AIDE Hugh Hazelrigg) (05/17/89)
In article <6101@nfs4.rl.ac.uk> kgd@inf.rl.ac.uk (Keith Dancey) writes: >My understanding is that the demise of the dinosaurs extended over a period >of order of magnitude of a thousand years. Certainly long enough to place >doubt upon the viability of a single catastrophy such as the one mentioned. What prevents the effects of a "single catastrophy [sic]" from propagating over a period of a thousand years? On a geological scale of time, the events of a thousand years constitute less than a footnote in a billion-page volume. Life on this planet seems to be pretty durable, in spite of its perceived fragility. We, the living, while certainly not immune from geological, meteorological, or cosmological influences, won't go away overnight unless the whole planet is blasted to smithereens in one swell foop! Look: a thousand years (or even five or ten) really is just a one-nighter (what a party!). The earth may have lost a host of magnificent species, but did life disappear? I believe the metorite/asteroid collision theory to be the best put forward to date to explain the demise of the dinosaurs and their ecosystem. Your objection, Keith, is ill-considered. Hugh Hazelrigg hazel@unm-la.lanl.gov Disclaimer: None. I don't work for anyone who doesn't trust me implicitly.
aiko@cs.odu.edu (John K Hayes) (05/17/89)
It just so happens there is an article in the current issue of Nat'l
Geographic (June, I think) that deals with mass extinctions. It says that
most scientists now believe that the extinction of the dinasaurs was caused by
a single event as opposed to a gradual dying out. They define the time
boundary of the Cretaceus (sp?) period (when there were dinasaurs) and the
Tertiary (sp?) period (when there weren't) as the K-T boundary. There have
been samples of quartz crystals found that date to around the K-T boundary
that show signs of stress to a degree such as that caused by a nuclear
explosion or an impact of a very large meteor.
There has also been found a pencil thin layer in a chunk of rock of an element
commonly found in meteors but rarely on earth. The layer in the rock where
this occurs corresponds roughly to the K-T boundary. They estimate the meteor
to have been about 6 miles across which would produce the equivilent of
10,000 times all the world's nuclear explosives.
As for what happened after the impact, scientists differ. Some propose that
90 % of the earth's forests caught fire. Some say that if the impact were on
land it would produce a thick smog that would cause extreme cold; but if it
were at sea, it would send so much water vapor into the atmosphere that a
greenhouse effect would produce extreme heat. One scientist who has been
studying the Yellowstone fire proposes that even if the impact were at sea
it would have produced an explosion so great that most of the world would have
caught fire (I forget the specifics she detailed, but they were very
interesting).
Still others (but a minority now, I believe) maintain that the cataclysm
can be explained by earthly causes such as ice ages, volcanic activity,
shifting of the continents, etc. But, there seems to be evidence that
suggests otherwise.
--
---{john hayes} Old Dominion University; Norfolk, Virginia USA
internet: aiko@cs.odu.edu
Home: (804) 622-8348 Work: (804) 460-2241 ext 134
<++++++++++++++++++++++++++++++++++>
Are you a Have or a Have_Not? Because if you're a Have_Not, you've probably
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give it away at some point in the future! --- The Clash
<++++++++++++++++++++++++++++++++++>kgd@inf.rl.ac.uk (Keith Dancey) (05/23/89)
In article <1128@unm-la.UUCP> hazel@unm-la.UUCP (Hugh Hazelrigg) writes: >In article <6101@nfs4.rl.ac.uk> kgd@inf.rl.ac.uk (Keith Dancey) writes: >>My understanding is that the demise of the dinosaurs extended over a period >>of order of magnitude of a thousand years. Certainly long enough to place >>doubt upon the viability of a single catastrophy such as the one mentioned. > >What prevents the effects of a "single catastrophy [sic]" from propagating over >a period of a thousand years? On a geological scale of time, the events of a >thousand years constitute less than a footnote in a billion-page volume. > True. But you are forgetting that geology was not the issue in the article on the relatively sudden extinction of dinasaurs. The issue was whether a single impact could effect *meteriological* conditions such that a species would become extinct. For instance, whether polluted skies would effect food chains and temperature. But if that scenario was to be true, then SURELY a species would die within its lifetime. If one dinosaur could survive its entire life under these conditions, then so could another, and so on. If dinosaurs took a thousand years to become extinct, what finished off the last one that *didn't* manage to kill its immediate forbears. If anything, one would assume that survivors of the first five hundred years would have been selected to manage better under the austere conditions, rather than the opposite. It is also reasonable to assume that these hostile conditions would *gradually* improve with time, thus *increasing* the chances of species survival, rather than the opposite. > >Look: a thousand years (or even five or ten) really is just a one-nighter >(what a party!). The earth may have lost a host of magnificent species, but >did life disappear? > When you are talking about *dramatic* changes in climate and food chains critically effecting species survival, then the time scales involved must be of the order of seasons, rather than thousands of years. One year of darkness is all that it would take to destroy vegetarian dinosaurs. But they lasted for generations. How? And if even a single generation could survive lower temperatures, why couldn't others? >I believe the metorite/asteroid collision theory to be the best put forward to >date to explain the demise of the dinosaurs and their ecosystem. Your objection, >Keith, is ill-considered. > Far from it. There are enormous problems with a *single* catastrophy such as an asteriod strike *if* the palaeontological evidence is to be believed (unless dinosaurs lived a thousand years, that is :-). -- Keith Dancey, UUCP: ..!mcvax!ukc!rlinf!kgd Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, England OX11 0QX Tel: (0235) 21900 ext 6756 JANET: K.DANCEY@uk.ac.rl.inf
leech@Apple.COM (Jonathan Patrick Leech) (05/24/89)
In article <6101@nfs4.rl.ac.uk> kgd@inf.rl.ac.uk (Keith Dancey) writes: >My understanding is that the demise of the dinosaurs extended over a period >of order of magnitude of a thousand years. Certainly long enough to place >doubt upon the viability of a single catastrophy such as the one mentioned. >If the palaeontological evidence is not contradicted (and I have understood >it correctly) then a *series* of such catastrophic strikes would be required. > >That is not say a single catastrophy is ruled out, but it looks as though >its effects must be longer-lived than a few years. There is some belief that a gravitational perturbation of the cometary cloud could produce "showers" of comets in the inner solar system. Don't take "showers" too literally - it means a handful of hits over long periods of time - but this has some bearing on your comments. Yow! Get off the net for two weeks, come back to 600 articles in sci.space. :-) Jon Leech (leech@apple.com) Apple Integrated Systems, San Jose __@/
lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) (05/25/89)
In article <6235@nfs4.rl.ac.uk> kgd@inf.rl.ac.uk (Keith Dancey) writes:
: True. But you are forgetting that geology was not the issue in the
: article on the relatively sudden extinction of dinasaurs.
: The issue was whether a single impact could effect *meteriological*
: conditions such that a species would become extinct. For instance,
: whether polluted skies would effect food chains and temperature. But
: if that scenario was to be true, then SURELY a species would die within
: its lifetime. If one dinosaur could survive its entire life under these
: conditions, then so could another, and so on.
Yes, but that's not really the issue. To guarantee eventual extinction
you only have to reduce the rate of survival (to reproductive age) to
less than 2 per dinosaur family. We all know that changes in
temperature affect fertility, not to mention fecundity... :-)
And there could well be some relationship between temperature and
mortality. Especially with large egg layers. So meteorology can
certainly have long term effects on a species.
(What actually happened was the dinosaurs had an industrial revolution with
all the iron in the asteroid, and the standard of living went too high,
and too many of them became dinks.)
: If dinosaurs took a
: thousand years to become extinct, what finished off the last one that
: *didn't* manage to kill its immediate forbears.
Probably loneliness. Only 1/3 :-)
: If anything, one would
: assume that survivors of the first five hundred years would have been
: selected to manage better under the austere conditions, rather than
: the opposite. It is also reasonable to assume that these hostile
: conditions would *gradually* improve with time, thus *increasing*
: the chances of species survival, rather than the opposite.
There are several things to say about that. If you trigger a mini ice
age it could well last longer than 1000 years. Moreover, as the
dinosaurs get sparser, it becomes more difficult to find a mate and
de-sparsify the dinosaurs, a nasty form of feedback. And even if
conditions are improving gradually, the land is now overrun with little
varmints who have a faster selection cycle and took advantage of the
new conditions while the bigger folk were still squeaking by. Perhaps
the initial catastropic conditions favored small critters that could
get by eating almost anything, even tough dinosaur eggs. Or malnourished
dinosaurs trying to babysit their eggs.
It's also vaguely possible that the dinosaurs adapted to the cold, but at
the price of losing the ability to adapt to the heat again. We don't know
enough about dinosaur genetics to rule it out. (At least, I don't.)
: >Look: a thousand years (or even five or ten) really is just a one-nighter
: >(what a party!). The earth may have lost a host of magnificent species, but
: >did life disappear?
: >
: When you are talking about *dramatic* changes in climate and food chains
: critically effecting species survival, then the time scales involved must
: be of the order of seasons, rather than thousands of years. One year of
: darkness is all that it would take to destroy vegetarian dinosaurs. But
: they lasted for generations. How? And if even a single generation could
: survive lower temperatures, why couldn't others?
Maybe they were allergic to the ragweed that grew so well in the cooler
climate. I think every day I spend in these Santa Ana winds takes several
hours off my life. (Beats having the smog though.)
If the chaoticists are to be believed, something much less dramatic
than an asteroid is capable much greater consequences than mere
extinction of dinosaurs. Why, the flap of a butterfly's wing today may
influence whether the universe collapses next week... well, perhaps
that's a wee bit exagerated... Still and all, non-linear systems (and
we're not just talkin' weather) can behave oddly under seemingly mild
perturbations. Let's remember that ecological niches aren't cast in
concrete, but at least partly in the flesh of whatever else wants to
occupy the neighboring niches, not to mention the same niche. And
precedence matters--last one there is a rotten dinosaur egg!
: >I believe the metorite/asteroid collision theory to be the best put forward
: >to date to explain the demise of the dinosaurs and their ecosystem. Your
: >objection, Keith, is ill-considered.
: >
: Far from it. There are enormous problems with a *single* catastrophy such
: as an asteriod strike *if* the palaeontological evidence is to be believed
: (unless dinosaurs lived a thousand years, that is :-).
It doesn't take much imagination to see that *something* changed to off
all the dinosaurs. Just because we have difficulty imagining how the
bullet got from the smoking gun to the victim doesn't mean it didn't (or did).
To bend another saying to our use, we might say that "Absense of imagination
implies imagination of absence." Just because I can't see the connection
doesn't mean there isn't one. The "enormous problems" with a single
catastrophe are mostly problems in our head, because we ain't smart enough.
(Nothing personal, Keith. :-)
I've got it now! The asteroid hit an oil field situated over a fluorite
deposit sitting on a huge salt dome, and filled the atmosphere with
chlorofluorocarbons. Anything that couldn't hide under a log and didn't
have fur or feathers had increased risk of skin cancer for the next
N thousand years. :-)
Yes, unlikely. But we don't know how many times Mother Nature tried before
she hit the jackpot. Unlikeliness isn't a big problem in my book.
Go ahead, flame me, I've already reproduced.
Larry Wall
lwall@jpl-devvax.jpl.nasa.gov
"So many programs, so little time..."jtk@mordor.s1.gov (Jordan Kare) (06/09/89)
In article <5000@jpl-devvax.JPL.NASA.GOV> lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) writes: >.... Let's remember that ecological niches aren't cast in >concrete... What about all those alligators living in the New York City sewer system?? Jordin Kare