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DA14 flyby & NASA's devastation predictions

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#1 photonovore

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Posted 08 February 2013 - 10:01 AM

I'm sure everyone has heard of the upcoming close flyby of the 46m rock, DA14. In reading the news reports and back-checking on NASA's PR about this event, i found in the "what did we miss" category all sorts of catastrophic scenarios predicted for an impact of an object of this size, density, velocity etc. Comparisons were made to Tuguska, where 1200 square km of forest was literally flattened, to claims of "city killer" and "regional devastation". ( NASA Q&A see: Q: What would happen if DA14 were to impact Earth?)

This sounded way off base to me and so i took the impact parameters from NASA's NEO page on DA14 (Earth Impact Risk Summary and Earth Impact Table) and entered the data into Melosh's Earth impact calculator. web page I got what i expected...at 1km from the terminus 84mph wind peak and glass breakage. That's it. The only way to get a significantly more devastating result would be to assume a perpendicular entry--which is so improbable as to be virtually impossible--rather than a 45degree path (most probable). But i suppose the former could be called the "worst case" scenario.

Anyway, here is a screenshot of the NASA impact page for DA14 (which was taken down and not replaced a few days ago--so i re-accessed it from google cache):

DA-14 Impact tables

and a screenshot from the Earth Impact Effects Program results for a DA14 impact: Impact effects

Perhaps they are using an improbable worst case scenario to help raise some public support for dangerous asteroid detection and mitigation funding? But what i see is just more misinformation & sensationalism (and coming from an organization which should do it's best to avoid both!)

(If i made any errors please point them out...)

#2 deSitter

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Posted 08 February 2013 - 10:13 AM

Wow, thanks for that. Very revealing.

-drl

#3 Carl Coker

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Posted 08 February 2013 - 02:34 PM

2.5 psi is enough to cause serious damage to many homes; the air blast won't just be breaking windows. In addition, notice that the calculator says the asteroid would break up some 8 km above the ground. This plays a large role in potentially mitigating the effects of the impact, since you're actually 8-9 km away from ground zero, not one. If the impactor managed to survive all the way to the ground, or even just much closer to it, the effects would be much more devastating.

Note that NASA says their mass estimate for the body is based on an assumed density and assuming that it is a uniform sphere. They acknowledge the fact that their mass estimate is only good to within a factor of three, since they haven't been able to actually measure it. If the asteroid is much denser than assumed (i.e., it is more of an iron asteroid than a rocky/stony one), the impactor would survive all the way to the ground according to the calculator. For example, if 2012DA14 were pure iron, you'd be very dead 1 km away from the impact site from a good ~350 psi of overpressure. Granted, iron asteroids are fairly rare, but they do exist, and I'm sure NASA considered the possibility that 2012DA14 is one of them.

#4 photonovore

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Posted 08 February 2013 - 10:17 PM

If the impactor managed to survive all the way to the ground, or even just much closer to it, the effects would be much more devastating.


Thanks for the thoughtful comments.
Enter 90 degrees in the calculator and you will see the difference 17,000 ft makes vis a vis airblast altitude!! *Very* significant--and as i said exceedingly unlikely. As for the density notice that 3000kg/m3 is what is entered. Calculated as a spheroid the mass estimate reduces to 2550kg/m3. It has a lightcurve amplitude of 1 magnitude which means it is definitely not anywhere near a spheroid, which most probably means a good deal of overestimation of mass is already built into the estimate.

Iron or stony? Spectral obs (Carnegie Institution) have placed this asteroid in the L-class, which, along with K-class, places it in the Eos family of S/C type stony asteroids. So the probability this is an iron asteroid is nil. Good thing too..as if there was any question, NASA might be treating us to images of the Barringer crater superimposed over New York City on the evening news, too! LOL!

The overpressure is more significant than indicated, valid point; this was interesting to investigate as well. Turns out the military built a number of different style/construction full-sized homes during nuclear tests in the 50's to measure destruction at various peak overpressures. The results can be read here --illustrated even. :) But even so this imagined event remains far short of the scale of the Tunguska event NASA seems intent on comparing it to: 4x equiv airblast and *40*psi overpressure within 4km radius! ref. .

#5 StarWars

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Posted 09 February 2013 - 03:10 AM




According to the news the asteroid will fly over Australia in the southern Hemisphere..

BTW, If NASA or JPL knows about an imminent impact they surly will not disclose this information to the general public. :(

#6 Motokid600

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Posted 09 February 2013 - 12:31 PM



According to the news the asteroid will fly over Australia in the southern Hemisphere..

BTW, If NASA or JPL knows about an imminent impact they surly will not disclose this information to the general public. :(


But wouldn't the general public eventually figure it out on their own? Well.. not general I guess. Astronomers.

#7 Skip

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Posted 09 February 2013 - 01:17 PM

BTW, If NASA or JPL knows about an imminent impact they surly will not disclose this information to the general public.


WHAT??? Where did you get this idea?

#8 gavinm

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Posted 09 February 2013 - 04:01 PM

The results can be read here --illustrated even. :)


Haven't seen that book in years. I did a computer science project in 1985(?) to simulate the slide rule/calculator that came with the book on a computer (an Apple 2). Fell to pieces years ago (the book, not the Apple 2 - I still have that) - thanks for the link.

#9 llanitedave

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Posted 09 February 2013 - 11:18 PM

BTW, If NASA or JPL knows about an imminent impact they surly will not disclose this information to the general public.


WHAT??? Where did you get this idea?


Well, we all know how surly they can be...

#10 Glassthrower

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Posted 10 February 2013 - 01:04 AM

There is also the possibility that an object is actually a swarm of smaller objects, although that is not the case here. A swarm of impactors will behave differently than a single mass and the effects seen on the ground will differ.

A truly worse-case scenario would be a fast-moving, long-period comet on an eccentric orbit. It would be like an rifle shot coming out of the dark with an element of surprise. With no prior observations in recorded history, coming in from the right (or wrong, depending on your perspective) angle from "behind" the Sun, and we would have very little advance warning.

Such comets and Oort Cloud objects typically travel at much higher velocities than wayward asteroids from the Main Belt or Kuiper Belts. Combined with a severe angle of entry, the effects would be devastating.

In any case, you wouldn't want to be anywhere close to the impact zone, even if the object is small and fragile.

For comparison, here is the most recent result of a crater-maker event here on Earth - http://en.wikipedia....as_impact_event

The Carancas impactor was a friable stony type, traveling quickly and at a severe angle. It's size was quite small in the grand scheme of space rocks at only 10-feet in diameter before atmospheric breakup. The resulting crater was approx. 43 feet in diameter and 15 feet deep. The shock wave shattered the windows of buildings a kilometer away from the impact site.

Carancas was not a major event in the Hollywood style, but had it struck in the center of a crowded urban-center, and not a remote area of rural Peru, the effects would have been much nastier.

It's fun to watch and speculate. If the calculations are wrong, and it wallops us, we'll survive. Just don't be anywhere in the direct vicinity when it hits. ;)

Best regards,

MikeG

#11 StarWars

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Posted 10 February 2013 - 03:59 AM




According to the news the asteroid will fly over Australia in the southern Hemisphere..

BTW, If NASA or JPL knows about an imminent impact they surly will not disclose this information to the general public. :(


But wouldn't the general public eventually figure it out on their own? Well.. not general I guess. Astronomers.




Possibly, the general public will believe whatever is on the national news.. :grin:

The asteroid will most likely end up in the ocean... :o

#12 Mister T

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Posted 10 February 2013 - 08:41 AM

Isn't "from "behind" the Sun" kind of like the dark side of the moon.

Anything approaching from "behind the Sun" would only be hidden for part of the year and would surely take many years to get here giving us a fairly good opportunity to discover it. :question:

#13 Glassthrower

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Posted 10 February 2013 - 10:39 AM

Sssshhhh....meteorites have nothing to do with astronomy. ;)

#14 photonovore

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Posted 10 February 2013 - 12:52 PM

The Carancas impactor story is interesting (i've been out of the loop so long i missed hearing about this.) The nature of the impact is certainly related to the site's >12,000 ft altitude...which may be a variable that the impact calculator should take into consideration? Other parameters equally constrained, the impact effects at, say, the high plateau zone of Bolivia, could be expected to be considerably different than at locations near sea level...

#15 Glassthrower

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Posted 10 February 2013 - 06:54 PM


Isn't "from "behind" the Sun" kind of like the dark side of the moon.

Anything approaching from "behind the Sun" would only be hidden for part of the year and would surely take many years to get here giving us a fairly good opportunity to discover it.


I think you are correct and I probably have my planetary blind-spots confused. Isn't there a part of the sky that gets less camera and telescope coverage, that is considered a blind spot? (maybe the poles or something?)

The Carancas impactor story is interesting (i've been out of the loop so long i missed hearing about this.) The nature of the impact is certainly related to the site's >12,000 ft altitude...which may be a variable that the impact calculator should take into consideration? Other parameters equally constrained, the impact effects at, say, the high plateau zone of Bolivia, could be expected to be considerably different than at locations near sea level...


I recall reading elsewhere (not Wikipedia) that Carancas was something of an oddball as far as incoming meteoroids are concerned. It was traveling on the higher end of the velocity realm for that type of object and the angle was much more vertical. And yes, I do also recall reading that the high altitude of the target site also played a factor.

Petrologically speaking, Carancas was brittle and even the remaining meteorites are very friable. They crumble into dust and crumbs readily, and a large quantity of mm-sized grains and sub-mm dust was recovered from the crater and immediate surroundings. Very few large fragments survived.

An iron meteorite would have changed the equation considerably.

That impact effects calculator is fun to play with isn't it? :)

#16 TVG

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Posted 10 February 2013 - 10:35 PM

I apologize if this has been addressed in the thread already, but does anybody know of a good asteroid star chart finder?
I looked on heavens-above, but could not find it. I believe we have a 33 hour window to see it?

Thanks,
Todd

#17 PhilCo126

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Posted 11 February 2013 - 09:21 AM

Western Europe will aim to observe between 09:00 and 10:30 PM as this asteroid will pass over the tail of the Ursa Major :bugeyes:

#18 TVG

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Posted 11 February 2013 - 09:51 AM

Okay thanks. I also found this website:
http://freestarcharts.com
Freestarcharts

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#19 photonovore

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Posted 11 February 2013 - 08:12 PM


I recall reading elsewhere (not Wikipedia) that Carancas was something of an oddball as far as incoming meteoroids are concerned. It was traveling on the higher end of the velocity realm for that type of object and the angle was much more vertical. And yes, I do also recall reading that the high altitude of the target site also played a factor.


i emailed Melosh over the weekend about the altitude of the impact site issue and he responded this am that it is indeed a relevant factor for a "narrow range of impactor size" but in accordance with KISS they chose to omit it from the calculator. He also said that the altitude of the Carancas site was indeed a factor affecting the ground effects.

That impact effects calculator is fun to play with isn't it?


Yep! At this point i'm pretty settled on the notion that NASA (and the parroting science media generally) chose to use the worst case disaster/scare scenario, extreme improbability notwithstanding, just to boost PR for NEO program funding. It's the only motive that makes sense.

#20 StarWars

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Posted 12 February 2013 - 07:54 PM

BTW, If NASA or JPL knows about an imminent impact they surly will not disclose this information to the general public.


WHAT??? Where did you get this idea?




What If.... :crutch::crutch:


http://news.yahoo.co...-132801477.html

#21 Matthew Ota

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Posted 13 February 2013 - 04:18 PM

One thing not brought up in this discussion is that the asteroid my have very low density, a rubble pile similar to 253 Mathilde. I am not sure of the entry/impact dynamics from such a low density NEO

#22 llanitedave

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Posted 13 February 2013 - 09:50 PM

Seems like that would be more of a smear than an impact.

#23 PhilCo126

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Posted 15 February 2013 - 06:03 AM

Great to hear that the Faulkes South telescope at the Siding Spring Observatory is operational and spotted asteroid 2012 DA14
http://lcogt.net/blo...a14-caught-film
:bow:
RefractorPhill

#24 Glassthrower

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Posted 15 February 2013 - 06:05 PM

After what happened in Russia yesterday, I wonder if there are still any fools who deny the intimate connection between meteorites and astronomy.

Keep your eyes on the skies! :)

#25 llanitedave

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Posted 16 February 2013 - 01:15 AM

Not to mention the connection between astronomy and geology!

It's all one big wonderful continuum.






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