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."

Comments

Not even in 2037

[brejc8]

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.

Re:Huh?

[WhiteBandit]

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.

Two choices:

[2nd Post!]

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.

Re:How reliable are these calculations?

[Anonymous Coward]

read the damn article

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
. / \
. / \
. / \
. /o \

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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Straight from the horse's mouth

[ralphh]

This from the NEODyS Risk 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."