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How We Knew AL00667 Would Miss Earth
jefu writes "In January there seems to have been an incident in which it was thought that an object (asteroid) in space might have hit the earth within a couple of days of being spotted. It did miss, though. This story (from NASA/Ames) talks about the discovery of the object and the process that astronomers went through to determine if the asteroid was or was not a threat."
what are requirements for such a rock to survive its way through atmosphere? I doubt that size is only thing that matters. material shoul'd be counted too.
/ss
It seems like you are suggesting that this new technological ability to detect NEO's and possible impacts as being similar to the "Boy who cried wolf" fable.
The problem is, as we all know, the wolf finally did arrive one day...
I find the number 667 Highly suspicious..
Is number 666 ever issued? A lot of numberiung systems miss this one out, in order to keep the religeously insane from freaking. For instance the UK number plate authority stopped using it a few years ago after complaints from some quarters.
So my real question is: Would this have -actually- been AL00666?
Spooky...
"Oops, I always forget the purpose of competition is to divide people into winners and losers." - Hobbes
true. Composition matters a lot too. For a given size, a "stony" or primarily rock asteroid will burn quite a bit more than it's "iron", or mostly metal counterpart.
Also, stony asteroids tend to explode if/when they reach the lower atmosphere. Comets, which are primarily ice and stone, are very unlikely (but not impossible - see tunguska) to survive entry.
Any of these are much stronger than an ICBM, of course.
"Faith: Belief without evidence in what is told by one who speaks without knowledge, of things without parallel." - A.B.
"We probably could have had something in place to shoot such a threat down if we had fully funded the Star Wars MDS project, but sadly geopolitics killed that project."
Doubtful. Weapons for bringing down delicate ICBMs -- even if they had surprised everyone and actually worked -- would be useless against a mountain of rock and ice moving at kilometers per second.
It would be like flicking peas at the Exxon Valdez.
To deal with large objects on a collision course we first need a few decades of warning. Given time, a little nudge can make a big difference. For a rock kilometers in diameter, even thermonuclear explosions count as nudges. If we only have a few months of warning; we're well and truly screwed.
Iz
that most people didn't hear about the asteroid until long after the near-miss was over. Seems to bring up the old argument of whether it'd be better to inform the public and try to do something about it or keep it under wraps and possibly die in blissful ignorance...
Using utilitarian calculations, you can actually compute whether or not the expected consequences of informing are preferable to the expected consequences of secrecy. It would go something like:
Inform if EU(i) > EU(s)
where
EU(i) = p(h) * (1 - p(prev)) * U(knowing)
EU(s) = (1 - p(h)) * U(nondisr)
where
EU(i), EU(s) are the expected utility functions of informing and keeping secret, respectively
p(h) is the probability of a hit
p(prev) is the probability that a hit could be prevented if known to the public
U(knowing) is the value people would place on knowing in advance if they were going to be dead tomorrow
U(nondisr) is the value people would place on the avoided distruption of a global panic (the economic + emotional "costs" saved)
Thus, whether to inform depends on:
- How certain are you that the asteroid will hit?
- How big do you think the disruption will be if word of potential impact spreads?
- Is there anything you can do, given that it is going to hit?
I think the first one is really important. It has repeatedly been shown in research that people do not react rationally to probabilistic information. Thus, telling the public that "there is a chance that an asteroid could hit us", even when qualified by a quantification of the probability to the best of our knowledge, could actually lead to a greater mis-assessment of the risk than if nothing were said of it.
This is, of course, not a question of probabilistic and utilitarian calculations. There is a "right to information" aspect to it, as well. A good formulation would be "where is the borderline between 'creating unneccesary panic' and 'respecting people's right to know'". I would say that if the expert is worried to the point of personally taking significant action based on the information, such as buying emergency supplies etc., then he should inform the general public.
Only the older American missiles which used their outer wall as the skin of the fuel tank. It saved on weight and gave them formidable acceleration. The Soviets always used separate tanks and a thick steel skin - largely because they never worked out how to build precision skins. Both of which gave their missiles a massive strength.
Both countries now use solid fuelled boosters which are much tougher.
And as for a grenade - why bother - you can use a wrench.
Best wishes,
Mike.
i think the real interpretation of the compound word "near miss" is that it was near, yet still a miss.
being critical of the term "near miss" being mutually exclusive is infact a mis-understanding of the term.
An asteriod 2" in size would be a significant impact if it hit you on the head! However, they can't watch EVERYTHING. They have to draw the line somewhere. 1km seems to be the size needed to possibly wipe out all life on Earth. Yes, 1/2km would do a lot of damage and kill a lot of the population of Earth, but some would still survive the initial impact. I would assume once all the 1km NEOs are charted by 2008 that they would move on to the smaller ones. Also, as shown by this article, they found a 30m and now know its orbit. It's not like they are just throwing out the data for objects smaller than 1km if they happen to find them. Such small objects, however, are not the focus of the search.
Depends on what the object's properties are, the local geology, etc. In many cases, most of the energy from an impact will "splash" back upwards, with relatively little lateral damage. An air burst spreads the carnage much more widely.
As an example, many military weapons, including the original 2 atom bombs, detonate shortly before impact.
"Faith: Belief without evidence in what is told by one who speaks without knowledge, of things without parallel." - A.B.
Let's just get this straight: according to the article, the initial data were of low precision, they implied a very large uncertainty in the asteroid's trajectory. (In the event, it wasn't even a near-miss -- it was millions of km off, several times the moon's distance.)
The large uncertainty meant that at any one moment before the conceivable (but very unlikely) arrival of the body at or anywhere near the earth, there was a very large area of uncertainty, in which the asteroid's actual point of arrival would be one tiny and uncertain spot, and the possible trajectories leading to earth would be represented by another tiny blob (tiny relative to the whole area of uncertainty), most probably located very far away from the spot containing the real asteroid.
Calculations on real computers often represent an area of uncertainty like this by a nominal position that is very roughly at the centre of the area of uncertainty, accompanied by a measure of the size of the area of uncertainty.
The fact that one can physically read from the printed result and see that nominal position separately from its accompanying measure of uncertainty, because of the way the figures are presented on screen or paper, that does not give the nominal position any reality.
It happened that the nominal position first calculated in the case of AL00667 would have been (if of zero error) a trajectory heading for earth. But it wasn't of zero error, nor even close.
The whole scare looks like an artifact of the way in which uncertain results involving a continuum are presented using discrete digits.
-wb-
What's heavier a ton of feathers or a ton of lead?
Would depend on how one measures and verifies the mass or weight of the material. Let's make the reasonable assumption that we're weighing both at room conditions (760 torr, 295 K) using a beam balance. The point is that feathers displace a lot more air than lead. This means that when we add enough feathers or lead to measure 1 kg, the mass of feathers is slightly more than that of lead (due to compensating for buoyancy in air etc). This applies even to a beam balance because the masses we use on the other pan are far smaller and denser than feathers.
Hence, "one kg" of feathers (as measured) has a real mass of about 1.01 kg, while "one kg" lead has a real mass of about 1.000091 kg. This difference is about 9.91 grams per kg measured, which adds up to 9.91 kg per metric ton measured.
Hence, "one metric ton" of feathers has 9.91 kg more matter in it than "one metric ton" of lead.
If you really want to answer that question satisfactorily, you must find measure out the masses AND verify the masses in a perfect vacuum.
Time flies like an arrow. Fruit flies like a banana.
I looked this info up during an earlier discussion of planet killing asteroids. Sorry, I don't have the references handy. My recollection was that it didn't matter what the composition was if it were only a little bigger than the estimated size of the Tunguska rock... IIRC if an asteroid were about 100 meters in diameter, it would be sure to strike the surface and dig a crater.
From the lack of a crater the Tunguska rock was seen as one of the more fragile kinds. But, in terms of killing a city, the mass and velocity of the rock is what matters most, not its composition. Nickel-Iron rocks are thought to be more robust, and able to survive to hit the surface, and dig a crater, even if they are smaller than Tunguska.
I also came across the very interesting suggestion that the Tunguska event may not have been extraterrestrial at all. Tunguska is an area with huge natural gas deposits. The other suggestion was that seismic activity allowed a jet of Natural gas to jet out, that its fumes had been accumulating for days, until lightning set it off. This theory explained some aspects of the Tunguska event that the asteroid theory didn't.
I just can't get out of my mind that ludicrous ending where the aging Sen.Jellison dramatically gets up and sends his minions to "give our children the lightning!" Their idea of good government did not appeal much to me either.
What I don't want to see is an orbital weapons platform deployed under false premises.
Yes, because putting weapons in an orbital platform is so much cheaper and more effective than housing them in silos in Kansas. Who knows what evil could come if Rumsfeld got his hands on a large, unprotected orbital concentration of weapons from which missiles could be launched only in well-described orbits that could be easily intercepted.
who are those slashdot people? they swept over like Mongol-Tartars.
I'd like to see a movie based on Lucifer's Hammer. It's more about life after the comet hits than the struggle for bruce willis to blow it up.
The days of the digital watch are numbered.
It seems to me that over the last few years I have heard a LOT of reports of asteroid near-misses - much more so than in the 80's or 90's. Unfortunately, I think it's going to take an asteroid/comet impact, over a population center, before the humans "in power" even begin to "get it."
Recent movies aside, the thought of a HUGE rock (or solid chunk of iron) falling from the sky, is so completely beyond the experience of most humans, as to be practically ludicrous.
"I would sooner believe that two Yankee professors lied, than that stones fell from the sky." - Thomas Jefferson (supposedly)
--==>>BobT>
From: Alan W Harris Date: Tue Jan 13, 2004 7:24 pm Subject: "Turn out the lights"
Brian Marsden has substituted a different orbit that fits the observations within allowed uncertainties. There has been no added or re-worked astrometry, just a little push of the solution off the covariance minimum. On the one hand, this demonstrates that the limited observations so far are not sufficient to predict an impact with high probability. On the other hand, nothing has happened to invalidate the previous solution or reduce the probability that it is right. I'm reminded of an old pilot's story of how to do a forced landing at night in a populated area. The advice is that in order to avoid plowing into population on the ground, find a large dark area with no lights. If you're lucky it will be a field of some sort and you can do a dead-stick landing. As you approach, turn on your landing lights and see what's there. If you like what you see, go ahead and land. If you don't, turn off your lights.
>>Right then, do the maths, and work out a ballistic trajectory that will get a missile more than 5500km, without leaving the atmosphere.
a tmospheric_structure.html
Rather than maths, lets look at facts.
from this page: http://www.d-n-i.net/fcs/comments/c439.htm
(look for section 4)
" A typical ICBM gets about 500 to 1000 miles above the ground at the highest point of its trajectory."
Now, lets see what I said, an ICBM doesn't have to go out the _atmosphere_...
From this page: http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/ATM_CHEM/
" The exosphere is the outermost region of the Earth's atmosphere. Within the exosphere, atoms follow ballistic trajectories and rarely undergo collisions because the density of atoms in this region is so low. The exosphere begins at approximately 500 km and extends outward until it transitions with interplanetary space (at roughly 10,000 km)."
[Just incase you need to know:
1000 miles = 1609.344km;
10,000km = 6213.712 miles (3dp for both)]
The exosphere, which is part of Earth's _atmosphere_ extends HIGHER than an ICBM's launch max height. So therefore, I can conclude that my original statment was correct.
If you feel like doing the maths, by all means, do so, but you are going to have to show me that the ICBM leaves the exosphere (yes, part of our atmosphere).
NeoThermic
Use my link above, or to view my server, NeoThermic.com
Sorry,
you are confusing mass with weight.
Your "beambalance" thingie says a lot about weight, and air pressure.
You might be correct about in which way the ballance would tip here on earth.
This has nothing to do with mass.
</nitpicker>
pAnkRat
--
"A bunsenburner.
What is a bunsen?
And why would one like to burn it?"
(Rincewind in the Discworld adventure)
we need an "-1 Plain wrong" moderation option!