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2004 MN4 Probably Won't Kill Us
Xshare writes "It's now official. NASA's Near Earth Objects page lists 2004 MN4, the asteroid that's been covered on slashdot recently, as having a 1 in 56,000 chance of hitting earth, and even then only in 2037. It seems that earth was near the edge of the cone of probability of when it could go. As the cone kept closing, the probability of hitting earth grew, but it kept getting closer to the edge. It's now outside the cone, and we can be safe."
That is the cumulative impact probability. The probability of impact in 2037 is actually 1 in 526,316,000 chance. The more likely one is in 2044 and that is 1 in 83,000 chance.
Mouse powered Chips, Open source Processors and Lego
So how exactly did we go from a 1 in 37 chance to a 1 in 56000 chance in a few hours? My guess is that slashdot submitters was posting meaningless statistics and editors were letting them through in order to sensationalize the issue.
Too bad you'd be guessing wrong. NASA's information page on 2004 MN4 has been continuously updated throughout the weekend. Just a few hours ago, based on certain observations, it was concluded that the probability was 1/37. After further calculations and observations, the trajectory of the asteroid was plotted with enough confidence to warrant a reevaluation of the impact probabilities. Hence, we now see a 1/56,000 chance. It's all right there on NASA's page. Nothing sensationalistic about it.
How'd we get arrive at those probabilities within a matter of hours? Read the article summary. It does a good job of explaining it.
You can do one of two things:
Trust the math
Do the math
I only briefly considered it but enough that I trust the math. It's not that the estimates are unreliable, it's that the estimates are only as reliable as the measurements made, and as the measurements become increasingly accurate in number and value, so too the estimate.
So the first estimate was made with a small number of measurements: The theoretical 'circle' of probability was large and intersected quite well with the Earth. As more measurements are made, the probability circle gets smaller, but because the size of the Earth doesn't shrink the chance of impact go up; more of the volume of the probability circle coincides with the Earth.
Then as even more measurements are made the circle grows ever smaller until it is small enough that only the edge of the circle is now overlapping the Earth, and thus the chance of impact goes down.
GPL Deconstructed
read the damn article
/o \
its quite simple
you have a cone of probable impact
. METEOR
. / \
. / \
. / \
. / \
. / \
./ o \
(o=earth)
its in the cone, high probability
calculations are more refined:
. METEOR
. / \
. / \
. / \
.
base of cone is smaller, earth now has an even larger chance of getting hit.. now some more narrowing of the cone:
. METEOR
. / \
. / \
. o/ \
oops.. earth is no longer in the cone.. probability just jumped to 1/56,000
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Lameness filter encountered. Post aborted!
Reason Please use fewer junk characters.
lalala In three days this has gone from 1/233 chance, to 1/45, to 1/56,000. How can there be so wide of a spread over such a small time interval if the method being used to estimate this is at all reliable? I could see how small trajectory changes in the asteroid would vary the predictions a lot if it were closer, but this is still 30+ years away.
What's to say tomorrow won't be 1/1? How is this latest measurement the final word that there is no threat
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See my post for an idea of how the math works.
The best way to visualize it: Imagine a dot on the ground. Cast a shadow on it from your hand. That shadow is the probable area where the future asteroid would be. As measurements become more accurate you would move your hand closer and closer to the ground. The probability goes up because the area of the shadow becomes smaller while the size of the dot on the ground (the Earth) remains the same. As the shadow continues shrinking then the probability of impact continues to go up until your hand gets so close to the ground that your hand touches (or misses) the dot..
At that point the shadow is either on the dot (impact) or it is off the dot (miss) and right now the shadow is off the dot (miss).
GPL Deconstructed
I will get to your question after this long paragraph.
The reason the probability of impact jumps around so much is as follows. The probability figure you have been seeing on the headlines is a CUMULATIVE probability of several potential impacts. In other words, they add the probability of the asteroid hitting Earth on this day, on that day, etc. for each close encounter. There were about 8 close encounters for which their probabilities were being summed to calculate this figure. There was a 1 in 38 chance for the asteroid hitting Earth on April 13, 2029, and this figure dominated the cumulative impact probability (1 in 37). Once more observations ruled out any impact on that day, the cumulative impact probability went to nearly zero. The remaining figure as of this posting, around 1.8e-05 (1 in 56,000), represents the probability of impact on the other close encounter dates (2037, 2044, etc.) as listed in the table [nasa.gov]. You will also note that the April 13, 2029 encounter has been REMOVED from this table. This is because there will be no impact; the table only lists remaining potential impacts.
Now, because they have ruled out an impact in 2029, some of the observations actually don't contribute to determining whether an impact will occur on the other, later dates (2037, 2044, etc). There have been hundreds of observations but the only ones relevant to the current potential impacts are counted on that NASA page.
"Near-Earth Asteroid 2004 MN4: improved situation
"The asteroid 2004 MN4 will have a very close approach to Earth in 2029. However, the observations collected by the astronomers, both professionals and amateurs, have provided enough information to exclude the possibility of an impact in 2029. This asteroid has an estimated diameter of 400 meters, and the nominal orbit solution results in a close approach to the Earth at 64,000 Km minimum distance on April 13, 2029. The actual distance could even be smaller, as small as 8 times the radius of the Earth. At the time of closest approach, the asteroid should be as bright as a fifth magnitude star, thus from some areas it will be visible to the naked eye.
"The sharp decrease in the estimated risk from this object was the result of the enormous work done by astronomers from all over the world. Notwidstanding the Christmas holidays, many dedicated people went to work in their observatories, in the archives of past observations and at their computers, as it was the case for the staff of NEODyS. More than 200 new observations of 2004 MN4 were obtained in the last 5 days. The discovery observations of June have been painfully remeasured, the impact monitoring computer programs have been run more than 30 times. Finally today some prediscovery observations from March 2004 were found and extracted from the archives of the Spacewatch survey. These allowed to extend significantly the observations time span, thus the confidence region for the orbital elements was sharply reduced and many impacts compatible with the previous data turned out to be incompatible with the extended observations."
"A worthy cause has never been harmed by the truth" - Gandhi
Our main fuel source is a non-renewable, polluting one that won't last us into the next century.
We use coal, oil, and natural gas because they're CHEAPER than other energy sources. When they actually DO start to run short the price will rise and we'll (incrementally) switch to using something else.
But don't use "known reserves" as a measure of how much is left. "Known reserves" measure how much has been hunted up. When enough for a few decades has been found it becomes uneconomic to hunt for more now, rather than waiting until later.
Early money is better than later money - because it can be put to work meanwhile. There is a crossover point where it makes more sense to put the money to work earning more money rather than hunt for more resources that you won't need for decades. The exact crossover point varies depending on interest rate and other factors (such as the planning horizon needed for your operation). But normally it's never more than 30 years in the future.
As a result, having "known reserves" good for more than about 30 years occurs only by accident: Either the last discovery made was enormous, or expected demand has dropped since the planning that ordered the last round of explorations.
But that means, if you assume known reserves are all reserves, you ALWAYS think you're "going to run out in 30 years" or so, and have a crisis. This has been true for the last 50 years at least, and people have been "viewing with alarm" and raising a big popular stink about it every decade or so for all that time.
I hear it has been going on for much longer. History records similar popular angst about running out of whale oil for lamps and limits to city size due to knee-deep horseflops in the streets from the delivery wagons. But I can attest to the doomsayers of the last 50 years or so from personal observation.
Yes, eventually the oil will run short. But there won't be a sudden catastrophy when the last well suddenly sucks dry. Instead the price will gradually rise, and the production gradually fall. First power plants, then cars, will switch to other fuels while the remaining production is used for more lucrative purposes (such as chemical feedstocks, until it becomes expensive enough that the chemicals will be synthesized some other way).
We still have billions of people living in utter poverty, and children aspire to be rock stars, and the likes.
And that's a total non-sequitur. So some people are in poverty. So what? That has no effect on whether some of the people who AREN'T starving will chose to spend some resources building mansions, watching football, touring the Moon, or colonizing space.
I don't think our (american/european) culture is ready to venture into space and colonize, we need to start putting value on the right ideals.
If america/europe doesn't do it first, somebody else will. That's how evolution works - for species, ideologies, corporations, and the couple dozen or so other things that have some of the characteristics associated with life. Nature red in tooth and claw. Every gene/meme for itself, and cooperation occurs only if it's advantageous for the cooperator.
Some groups die out. Some find new, more successful, niches. But those that put expansion into new opportunities on the back burner until they have "perfected" themselves lose out to those who ignore such hand-wrining and "boldly go".
You snooze, you lose!
I'd hate to see these ideals brought into space. Militarization of space? No thanks.
So your feelings will be hurt. Space is already militarized, and has been since the first shots. The entire process evolved from a war effort.
Right now we have ICBMs and spy satellites as major parts of military strategy. The {apparent} lack of always-up orbiting nuclear bomb platforms (to suplement the always-up bombers and always-down submarines) is an artifact of the dance that brought all-out war to a screeching, no
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The method for computing probabilities is not at fault. Simply more data has been coming in to nail the position and orbit of the roid.
How is it that the probability can change by over 3 orders of magnitude within a week---a full 30 years or more before the event itself?
Typically, the first orbit is computed with just 3 observations, and the first probabilities are given from this rough orbit. Remember that each observation for a position has an associated error to it. If I remember correctly, the MPC tipically assign 6 arcseconds of uncertainty or more to positions given by amateurs, and that is a lot of kilometers at 1 AU. So the initial orbits are quite uncertain.
An object that might hit the earth generates a lot of interest among astronomers, both hobbyist and professionals. In the days following the discovery, many new observations are performed, which quickly leads to a better determination of the orbit. This allows in turn to updated probabilities of hitting the earth.
As for the 30 years in advance, well it's celestial mechanics, good old Newton's Law.
It might behoove them to hold off on reporting the numbers until that log-variance dips below a certain amount---at least when the event is so far out.
This is actually not in our interest: if the number are not reported, the new data does not comes in and a better orbit cannot be computed.