Astro-Alert from Sky and Telescope:

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Wow! Close call!

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T. Anderson

would this asteroid burn up int the earth's atmosphere?

Heh. Objects of this size 'hit the earth' every year, about once a month. On September 27th of last year, one passed within 88,000km. It is somewhat amusing that objects which pass closer and closer get a good deal of press, but the ones of similar size that hit us are not on the radar whatsoever.

Of course, if it were up to me, both classes of objects would get the greater attention they deserve...hopefully the most important aspect of this, the very short lead time (understandable given the object's small size), and that of other such objects, impacting or not, will receive more than token press. It's really pretty disturbing.

Ah, The Daily Show had a bit on Senda. Hmmm...

Somebody correct me if I'm wrong, but I was under the impression that the "one a month" was for objects in the 5-10 meter range.

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T. Anderson

Depends on its composition.

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

The reports I've seen run from 10 to 15 a year, but I wouldn't suggest it is consistent by any means.

And yes, the object would burn up if it were of a less dense composition. If not, small fragments may survive entry.

As example, there was an object reported to be house-sized that entered the skies above spain on January 4th, 2004. Several fragments touched down as meteorites - one can be seen here. Another report, and some video of the fireball, can be found here.

A two-story, 5 bedroom house, at least.

A solid nickel-iron meteor that size would probably survive atmospheric entry pretty much intact. It would also make a good sized hole in the ground!

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

The closer it gets, the bigger it gets. Now they say 30 meters in diameter. That's more than 3 times bigger than 20 meters (in volume).

Well, depends on which state is your baseline. In Alabama that would be a decent-sized, repossessed doublewide with green pine deck, which would, of course, burn to bits in the upper reaches of the ionosphere.

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Remember, the vast majority of these that make it to the surface either land in an ocean or in a remote, unpopulated area. One of these days, though...

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I heard that this one in particular was only 100 feet, is that right

100 feet is 30 meters, which is 10 meters larger than the 20 meters stated in the original posting and the same as stated just a few posts above you ;-)

I dont understand the "was only", which makes it appear like you feel 100 feet is less than 20 or 30 meters

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I was trying to see if it would be visible here when dark comes, but I think it will making its return to space around dusk. According to this anyway. I think my astro-alert said the brightest would be Mag 10.

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Darnit! I wont be able to watch it go by from here.

How big! I mean, what would happen if this nickel-iron met hit the ground near a populated area. There is any study about the composition of 2004 FH?

Astronomer Steve Chesley of JPL (on CNN):
CNN story

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Hmmm - well, there are at least 3 in the last 6 that I can think of off the top of my head, mentioned in this post - once every two years is not accurate at all. Very odd.

So what happens after the trajectory shifts 15deg.?
http://www.space.com/scienceastronom...by_040318.html

Does it go around the sun and come straight at us next year?

Or, will it take a few more passes?

I wanna see fireworks

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Astronomy is looking up... :)

I wanna be far enough away to be able to say "What was that?" :wink:

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

heh heh...I saw that too...most excellent.

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The koo koo´s and the woo woo´s are having a feelday over this on GLP

CNN.com's poll today was "Do you worry about an asteroid hitting Earth?". As of 3:37 EST, about 143,000 people had responded and only 14% said yes. I guess its good that the majority don't worry, but its not good to convince the governement to fund NEO research.

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This would be an interesting test to see if we could launch a missile and hit it. I'm sure theres an ICBM laying around somewhere. It would be fantastic to try to hit it and observe what happens.

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Eagle Eye Observatory

I've tried to calculate how much energy the thing would deliver assuming it's 100 ft in diameter and traveling at 24 miles per second.

If it's made of rock, it would be carrying about 6.7 megatons worth of kinetic energy as it reached the upper atmosphere. If it were iron, that would rise to about 21 megatons.

In Richard Norton's book, "Rocks from Space", there's a chart that shows that a 1000 ton object, about 4 times smaller than this object, would retain 70% of it's initial velocity on impact. Another chart shows that at this speed, about 55% of the original mass could be retained to the ground. Assuming that the rock could reach the ground, it would deliver about 1.8 megatons...this probably wouldn't happen, though, since most rocky meteoroids blow apart high in the atmosphere. There'd be a big light show and a good shock wave, but probably no impact. The iron would be a different story. It would hold together very nicely and deliver about 5.3 megatons of energy on impact...instant tourist attraction.

A big iron meteorite struck in the Sikhote-Alin region of the Soviet Union on 12 February 1947...the biggest crater was about 87 feet in diameter and 20 feet deep; but the meteorite that caused this damage was much smaller than the one that missed us today.

Arithmetic errors and such aside...I'm glad it missed!

You can play around with speeds, sizes, and types on this page. A couple of quick entries gives a Tunguska-style atmospheric explosion for an ice or rock meteor of the given size, and a close to 1-km crater for an iron one.

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thanks for the great link ToSeek

It's one of my favorites. If you want to get Marvin mad, though, send a 9999 km iron asteroid into Mars.

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LOL reminds me of Marvin The Paranoid Android from Hitchhiker´s Guide to The Galaxy