2004 MN4, Even Higher Probability

phreakuencies writes "Worried since the recent post about the MN4 2004 asteroid, I added a bookmark to its 'impact risk' section at NASA. The asteroid started as having a 1/233 probability of hitting earth. Later it raised to 1/63. Daily computations made on 25 Dec raised its chances up to 1/45. Optimists can now say it has a 97.8% probability of missing earth." And Veteran writes " NeoDys offers the 'Orbfit' software package (source code released under the GPL) which can be used to get a pre-release view of the situation with Asteroid 2004MN4."

Comments

Impact calculator

[Nine Tenths of The W]

Just to reassure you
http://janus.astro.umd.edu/astro/impact/
The impact comes out as somewhere between 450MT and 1.6GT, depending on speed and composition

Re:Something to bear in mind

[barawn]

That's not necessarily true. It depends on the characteristics of the error.

If the errors are Gaussian, if the nominal trajectory (i.e. "it misses the Earth by X+/-Y km") is accurate, but imprecise (that is, X is correct, but Y is large compared to X) then the probability of impact will decrease as the precision is improved (i.e. as Y decreases) because the "Earth impact" possibility moves farther out on the fringes of the observation, and the area doesn't shrink fast enough to compensate for this.

Of course, if the errors are flat (all solutions are equally likely - actually, if the PSF falls off slower than the area shrinks) then you're correct. I'm pretty sure that they're Gaussian, or approximately Gaussian, though. So the only way the probability could be increasing is if the nominal trajectory's impact parameter is decreasing - that is, closer impact.

Re:Party like it's 2099

[TimToady]

Sorry, it's aimed mostly at the eastern hemisphere. If it hits, it'll be at about 9:22pm in London (.89 of a day at UTC), and since the rock is coming in almost directly from the night side of the planet, it's mostly aimed about 3 zones east of London plus or minus 6 hours. Or were you thinking that Iraq would have been renamed "Texas" by then?

Re:Common mistake in press coverage

[angel'o'sphere]

Well, seems you don't get the problem.

Simple map of the Earth moon Sysstem:

1 _ _ _ 10 _ _ _ 20 _ _ _ 30 _ _ _ 40 _ _ _
E ... m

Simple map of the path of the asteroid:

/ / / ... ... / / /

That should be 42 stripes but the junk char filter ....

As you see, the first stripe hits earth, the other 41 don't hit. Well, moon is in fact at opposite position when the asteroid comes in, but it was difficult to "draw" that. So, remember moon wont be hit.

Further observations of the asteroid will give us more data to determine wether the asteroid will travel stripe number 1 or 2, or wether it will travel stripe number 20 or 30 or whatever.

If we figure the asteroid is traveling NOT stripe 1 we are 100% certain that it will miss us.

If we figure the asteroid will not travel stripes 31 to 42, the likelyhood of an impact increased to 1:30.

Both calculations are "100%" certain. OTOH, your parent was right. The likelyhood that the chance of getting hit decreases is high. You have 42 draws ... and in 41 draws you have the chance that stripe number 1 -- the stripe which hits earth -- is removed from the set or possible pathes. Because more accurate measurement shows that the asteroid wont go that path/stripe.

angel'o'sphere