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Posted by: volcanopele Feb 15 2013, 07:01 AM

Looks like a small meteoroid decided to spoil 2012 DA14's big day by exploding over Russia...

http://zyalt.livejournal.com/722930.html?nojs=1

Posted by: Explorer1 Feb 15 2013, 07:18 AM

Depends on one's definition of 'small'! Phil Plait has an early summary/videos: http://www.youtube.com/watch?feature=player_embedded&v=rflTN4XAt34
The biggest over a populated area in a long time...

Posted by: Fran Ontanaya Feb 15 2013, 08:16 AM

Some info:

http://rt.com/news/meteorite-crash-urals-chelyabinsk-283/

http://rt.com/news/russia-meteor-meteorite-asteroid-chelyabinsk-291/

Posted by: nprev Feb 15 2013, 08:27 AM

Clearly a major event. I hope that the reported injuries are mild, and that there are no fatalites.

Caution all to be objective (as all have been thus far) and most of all respectful since there does seem to be a possibility of direct effects on people here, okay?

All that being said: There is no amount of 'wow' I can adequately express. Looking forward to the final analysis of this.

Posted by: Explorer1 Feb 15 2013, 08:43 AM

Direct hit on factory? http://www.youtube.com/watch?v=DgZ0aA7RUhE

Crews clearing rubble like just another day at work. i know that statistically Russia is the most likely country to get hit since it's got the greatest surface area, but literally a half day before this other rock is a real coincidence.

Posted by: machi Feb 15 2013, 11:15 AM

Chelyabinsk's bolid from http://www.flickr.com/photos/eumetsat/8474853633/.

Posted by: nprev Feb 15 2013, 11:50 AM

And that's in fact what it is precisely. Preliminary reports indicate that the object entered from a completely different azimuth than what would be possible for something associated with that asteroid during the upcoming encounter.

Posted by: belleraphon1 Feb 15 2013, 01:01 PM

WOW!...

Hope injuries not serious.

Analysis of this should be fascinating.... a mini-Tunguska.


Craig

Posted by: dvandorn Feb 15 2013, 01:10 PM

The best of the videos I've seen show the contrail ending well above the ground, suggesting that the impactor disintegrated in the air. I'm wondering whether the bolide actually hit the ground, or whether the damage was caused by an over-pressure wave pushed ahead of it.

-the other Doug

Posted by: dilo Feb 15 2013, 01:26 PM

An hour ago, Italian television told about russain military attempt to intercept/destroy the meteorite in flight, through a non-armed missile... I am very skeptical, did someone heared such a story? They showed also an impressive video with a ground explotion near an highway (metoerite fragment hitting ground?)

Posted by: machi Feb 15 2013, 03:33 PM

Dilo, today's SAMs cannot hit and destroy such asteroid. Radar has limited range and limited reaction time and even ABM missiles cannot cope with object with speed more than ~7 km/s. It's total nonsense.

Posted by: dilo Feb 15 2013, 03:46 PM

Yes, machi, I know and I said I was skeptical! in fact, it seems such rumor was officially denied...

Posted by: TheAnt Feb 15 2013, 03:56 PM

Several pieces did hit the ground, images of that factory shown above is only one that might have been a smaller piece.
A somewhat larger impacted near a highway.
And one piece thought to have been larger is said to have ended up in a lake quite far from the city according to my teletext news here.

@dilo: Hard to say, my teletext feed states that there initially were one alert for one possible nuclear strike, but it reads as that alert came after the actual impact so I guess the Italians have elaborated on that fact a bit.

@nprev: The teletext say about 900 wounded, mostly from shattered glass, and a number (no numbers given) hospitalized. But still no mention of any casualties so lets hope there were none.

Posted by: Phil Stooke Feb 15 2013, 04:05 PM

The story about intercepting the meteorite is almost certainly a journalist's confusion between the current event and stories about future asteroid deflection missions, which are being discussed in Russia.

Phil

Posted by: Mongo Feb 15 2013, 04:08 PM

I am trying to get an estimate of the size of the meteoroid and explosion. Assuming a dense rocky composition with a density around 3 tonnes per cubic metre, I keep getting sizes much larger than the estimate of around 10 tonnes that I have heard. The calculation below results in a mass of around 73,000 tonnes.

The overpressure from the blast wave was sufficient to shatter thousands of windows (and in fact some videos I have watched appear to show that every window in view was smashed) and caused the partial collapse of a zinc factory. This implies that the overpressure was between 1 kPA (shatters many windows) and 5 kPa (partial collapse of some buildings), let's assume that the zinc factory was poorly maintained and the overpressure was 3 kPa.

Early reports give an entry velocity of around 30 km/s.

According to http://impact.ese.ic.ac.uk/ImpactEffects/, the diameter of a rocky object that produces a 3.1 kPa overpressure at a distance of 30 km from directly under the main explosion (as appears to be roughly the distance from the videos) would be about 36m, producing a 5.26 MT airburst at an altitude of 18.2 km.

Earth Impact Effects Program
Robert Marcus, H. Jay Melosh, and Gareth Collins

Please note: the results below are estimates based on current (limited) understanding of the impact process and come with large uncertainties; they should be used with caution, particularly in the case of peculiar input parameters. All values are given to three significant figures but this does not reflect the precision of the estimate. For more information about the uncertainty associated with our calculations and a full discussion of this program, please refer to this article

Your Inputs:
Distance from Impact: 30.00 km ( = 18.60 miles )
Projectile diameter: 36.00 meters ( = 118.00 feet )
Projectile Density: 3000 kg/m3
Impact Velocity: 30.00 km per second ( = 18.60 miles per second )

Energy:
Energy before atmospheric entry: 3.30 x 10^16 Joules = 7.88 MegaTons TNT
The average interval between impacts of this size somewhere on Earth is 539.1 years

Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).
The impact does not shift the Earth's orbit noticeably.

Atmospheric Entry:
The projectile begins to breakup at an altitude of 63100 meters = 207000 ft
The projectile bursts into a cloud of fragments at an altitude of 18200 meters = 59600 ft
The residual velocity of the projectile fragments after the burst is 17.3 km/s = 10.7 miles/s
The energy of the airburst is 2.20 x 10^16 Joules = 5.26 MegaTons.
No crater is formed, although large fragments may strike the surface.

Air Blast:
The air blast will arrive approximately 1.77 minutes after impact.
Peak Overpressure: 3100 Pa = 0.031 bars = 0.44 psi
Max wind velocity: 7.21 m/s = 16.1 mph
Sound Intensity: 70 dB (Loud as heavy traffic)

edit -- Assuming that the distance from ground zero was 15km instead of 30km, and with an overpressure of 2 kPa, the website gives the following (calculated initial mass 51,000 tonnes):

Your Inputs:
Distance from Impact: 15.00 km ( = 9.32 miles )
Projectile diameter: 32.00 meters ( = 105.00 feet )
Projectile Density: 3000 kg/m3
Impact Velocity: 30.00 km per second ( = 18.60 miles per second )

Energy:
Energy before atmospheric entry: 2.32 x 10^16 Joules = 5.53 MegaTons TNT
The average interval between impacts of this size somewhere on Earth is 410.7 years

Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).
The impact does not shift the Earth's orbit noticeably.

Atmospheric Entry:
The projectile begins to breakup at an altitude of 63100 meters = 207000 ft
The projectile bursts into a cloud of fragments at an altitude of 19900 meters = 65400 ft
The residual velocity of the projectile fragments after the burst is 18.3 km/s = 11.4 miles/s
The energy of the airburst is 1.45 x 10^16 Joules = 3.47 MegaTons.
No crater is formed, although large fragments may strike the surface.

Air Blast:
The air blast will arrive approximately 1.26 minutes after impact.
Peak Overpressure: 2120 Pa = 0.0212 bars = 0.301 psi
Max wind velocity: 4.96 m/s = 11.1 mph
Sound Intensity: 67 dB (Loud as heavy traffic)

another edit -- this is the minimum value that reliably breaks windows, it still results in a calculated airburst energy of 1.9 MT with an initial mass of 31,000 tonnes. I doubt that the airburst was this close to overhead, it appeared closer to the horizon in the videos.

Your Inputs:
Distance from Impact: 10.00 km ( = 6.21 miles )
Projectile diameter: 27.00 meters ( = 88.60 feet )
Projectile Density: 3000 kg/m3
Impact Velocity: 30.00 km per second ( = 18.60 miles per second )

Energy:
Energy before atmospheric entry: 1.39 x 10^16 Joules = 3.32 MegaTons TNT
The average interval between impacts of this size somewhere on Earth is 277.4 years

Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).
The impact does not shift the Earth's orbit noticeably.

Atmospheric Entry:
The projectile begins to breakup at an altitude of 63100 meters = 207000 ft
The projectile bursts into a cloud of fragments at an altitude of 22500 meters = 73700 ft
The residual velocity of the projectile fragments after the burst is 19.6 km/s = 12.2 miles/s
The energy of the airburst is 7.95 x 10^15 Joules = 1.90 MegaTons.
No crater is formed, although large fragments may strike the surface.

Air Blast:
The air blast will arrive approximately 1.24 minutes after impact.
Peak Overpressure: 994 Pa = 0.00994 bars = 0.141 psi
Max wind velocity: 2.33 m/s = 5.22 mph
Sound Intensity: 60 dB (Loud as heavy traffic)

Posted by: jasedm Feb 15 2013, 04:34 PM

Wow!!

That's amazing. Inevitable comparisons to Tunguska will be made, but very fortunate this wasn't of that magnitude. Hope all ok

Jase

Posted by: ElkGroveDan Feb 15 2013, 06:22 PM

With all those videos there's no doubt an exact and precise trajectory can be computed and I would assume a possible range of orbits extrapolated.

Posted by: Gladstoner Feb 15 2013, 06:45 PM

.

Posted by: dvandorn Feb 15 2013, 06:51 PM

I can certainly see how there was a pretty big explosion in the air, there is a rather extreme pulse of light and then the contrail sort of vanishes. But -- a 500 megaton explosion only 18 km up, over a populated town, and all we had from that was a bunch of broken glass? I mean, that's more powerful of an explosion than the Tsar Bomba, the largest thermonuclear explosion that has ever been accomplished, and that explosion caused the clouds to move at hundreds of miles an hour away from the blast at distances of 20 to 30 miles. I sure don't see that kind of immense airburst in the videos of the bolide....

-the other Doug


Edit:
oops -- just reviewed the figures, and either I misread the megatonnage the first time through or Mongo adjusted his figures. Still, a 5 MT bomb packs an awfully big punch...

Posted by: Gladstoner Feb 15 2013, 07:00 PM

.

Posted by: dvandorn Feb 15 2013, 07:07 PM

FYI, NASA TV is running live coverage of the closest approach of DA14 2012 from JPL, with some live feeds from telescopes in Australia, where the asteroid is currently traversing the sky.

-the other Doug

Posted by: Mongo Feb 15 2013, 07:11 PM

I am waiting for a video that includes both the main flash and the arrival of the shock wave. That would allow us to estimate the distance and height above the ground of the detonation, and hence the minimum energy needed to cause at least 1 kPa of overpressure. I am betting it will be a figure in the low megaton range. A low kiloton-range explosion is already excluded in my opinion. The interval between explosion and shock wave hitting would have been too short, in the 20-30 second range, which I believe is already ruled out from the existing videos.

Posted by: dvandorn Feb 15 2013, 07:14 PM

Oh, cool -- the JPL visualizations manager is showing DA14 on Eyes on the Solar System.

-the other Doug

Posted by: TheAnt Feb 15 2013, 07:16 PM

Yes, this one is a http://www.youtube.com/watch?v=rWcklw9i45Y

Posted by: ugordan Feb 15 2013, 07:39 PM

Tunguska was in recent years re-estimated to have been around something like that. This clearly had to be less. How much less depends on the actual altitude of the "airburst". At 10 km, a Hiroshima-type burst seems plausible to me. To be in the megaton range, it would have had to be significantly higher up, otherwise I'd expect much more extensive damage below. But these are all just my W.A.G.s...

http://www.nasa.gov/topics/solarsystem/features/russianmeteor.html is estimating this to be around a 15 meter object and they're calling this one the biggest one after Tunguska. Doesn't say what their estimates are based on.

Posted by: Mongo Feb 15 2013, 07:57 PM

The http://impact.ese.ic.ac.uk/ImpactEffects/ gives the following results for a 15m object with density adjusted to produce a 1 kPa overpressure at a realistic distance given the videos. Total mass would be about 13,000 tonnes for an energy release of 830 KT.

Your Inputs:
Distance from Impact: 15.00 km ( = 9.32 miles )
Projectile diameter: 15.00 meters ( = 49.20 feet )
Projectile Density: 7200 kg/m3
Impact Velocity: 30.00 km per second ( = 18.60 miles per second )

Energy:
Energy before atmospheric entry: 5.73 x 10^15 Joules = 1.37 MegaTons TNT
The average interval between impacts of this size somewhere on Earth is 140.0 years

Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).
The impact does not shift the Earth's orbit noticeably.

Atmospheric Entry:
The projectile begins to breakup at an altitude of 28500 meters = 93400 ft
The projectile bursts into a cloud of fragments at an altitude of 16200 meters = 53100 ft
The residual velocity of the projectile fragments after the burst is 18.8 km/s = 11.7 miles/s
The energy of the airburst is 3.47 x 10^15 Joules = 0.83 MegaTons
Large fragments strike the surface and may create a crater strewn field. A more careful treatment of atmospheric entry is required to accurately estimate the size-frequency distribution of meteoroid fragments and predict the number and size of craters formed.

Air Blast:
The air blast will arrive approximately 1.11 minutes after impact.
Peak Overpressure: 1050 Pa = 0.0105 bars = 0.149 psi
Max wind velocity: 2.47 m/s = 5.52 mph
Sound Intensity: 60 dB (Loud as heavy traffic)

Posted by: ugordan Feb 15 2013, 07:59 PM

http://www.youtube.com/watch?v=SRSrdOfbnHI in particular shows a very long delay between start of filming and shock arrival, but it's obvious from the viewing angle that it's a ways off from the groundtrack so a minimum slant distance (here at least 23 km) is all we can infer. It does also show an unseen building smoking, perhaps it's the collapsed roof of the zinc factory. That amount of damage at that kind of range seems to support a high kiloton range. However, it's dangerous to infer too much from blast effects at these ranges as they start to depend upon meteorological conditions - inversion layers in the atmosphere, etc.

If the burst was at 20-ish km, I personally would place a bet at around 1 MT.

Posted by: ugordan Feb 15 2013, 08:09 PM

This just in, via NASASpaceflight.com: a http://www.youtube.com/watch?v=gQ6Pa5Pv_io from the flash to the sound. Whopping 2m 21 sec delay! Bolide starts at around 4:30 in the video.

This sucker was big!

Posted by: Mongo Feb 15 2013, 08:21 PM

Holy Cow! Even at that distance, it broke windows! Assuming an overpressure in that video of 0.95 kPA, the overpressure at the distance of the closer videos (with the explosion at about a 45 degree elevation from the horizon) would be about 1.18 kPa, which might be enough to cause the documented damage at the zinc factory, assuming that it was poorly constructed and maintained. So around 1.33 MT at minimum, it could be greater than that.

Actually, if the calculated energy release is correct and the zinc factory was directly under the main part of the explosion, the overpressure would be about 1.37 kPa, making the actual observed damage to the building more plausible, albeit still rather excessive for the calculated overpressure.

Your Inputs:
Distance from Impact: 43.00 km ( = 26.70 miles )
Projectile diameter: 19.00 meters ( = 62.30 feet )
Projectile Density: 6000 kg/m3 (rocky-iron)
Impact Velocity: 30.00 km per second ( = 18.60 miles per second )

Energy:
Energy before atmospheric entry: 9.70 x 10^15 Joules = 2.32 MegaTons TNT
The average interval between impacts of this size somewhere on Earth is 210.0 years

Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).
The impact does not shift the Earth's orbit noticeably.

Atmospheric Entry:
The projectile begins to breakup at an altitude of 37000 meters = 121000 ft
The projectile bursts into a cloud of fragments at an altitude of 18000 meters = 59100 ft
The residual velocity of the projectile fragments after the burst is 19.5 km/s = 12.1 miles/s
The energy of the airburst is 5.58 x 10^15 Joules = 1.33 MegaTons.
Large fragments strike the surface and may create a crater strewn field. A more careful treatment of atmospheric entry is required to accurately estimate the size-frequency distribution of meteoroid fragments and predict the number and size of craters formed.

Air Blast:
The air blast will arrive approximately 2.35 minutes after impact.
Peak Overpressure: 950 Pa = 0.0095 bars = 0.135 psi
Max wind velocity: 2.23 m/s = 4.99 mph
Sound Intensity: 60 dB (Loud as heavy traffic)

Posted by: Bill Harris Feb 15 2013, 08:57 PM

It will be interesting to see what the "yield" of this bolide calculates out to be. I don't know how much of an exact correlation between the the yield of an atomic device and this asteroid will be. A bomb is designed to stay smallish and compact as the fission/fusion reaction is taking place and then the fireball can expand at it's own rate. An asteroid is either a rubble pile of coalesced fragments or a highly fractured rock. On atmospheric entry the surface is very hot and ablative while the interior is still deep-space cold, It holds together until the aerodynamic stresses cause it to rupture into many fragments. At that point the surface:volume ratio goes very high and who knows what the dynamics of that is.

At any rate, this was a nice surprise. In the media I've heard the size of the passing asteroid mistakenly listed as "half the size of a football" (not of a football field) and my first thought was "Ha, how ironic, this meteorite was probably half-football sized", but from what I read here, it was somewhat bigger.

We should be able to collect many fragments that made it to ground-- the snow ought to help spotting the impact sites.

--Bill

Posted by: Explorer1 Feb 15 2013, 09:01 PM

At 19 seconds in TheAnt's video (post 311), is that an actual shockwave visible, or just a reflection from the windshield? It doesn't show up in the other footage, so I'm inclined to the latter.

Posted by: helvick Feb 15 2013, 10:31 PM

Why are we assuming that 1kPa is the level that would break glass/windows? All of the references I can find put the breaking glass level at around 5-10kPa overpressure but I assume there are other factors that would vary that in a shock wave scenario.

Posted by: Mongo Feb 15 2013, 10:58 PM

I used http://www.hsl.gov.uk/media/91722/hutchinsonmedalpaper.pdf as a reference:


http://boards.straightdope.com/sdmb/archive/index.php/t-478221.html has the following overpressures:


Since 1 kPa = 0.145 PSI, the kPa equivalents would be:

0.3 kPa Loud noise (143 db); sonic boom glass failure.
1.0 kPa Typical pressure for glass failure.
3.5-7 kPa Windows usually shattered; some window frame damage.

Some of the videos clearly show the window frames being heavily damaged and even crushed inward, suggesting an impact at the higher end of the overpressure range, but on the other hand the shock wave must also count as a sonic boom, lowering the needed overpressure by a factor of 3.5 or so. My best guess is that the damage normally expected from a 3.5 kPa overpressure is actually due to a 1 kPa sonic boom overpressure.

Posted by: machi Feb 15 2013, 11:28 PM

Mongo:
I don't know how it's today, but in earlier times (20th century), lots of Soviet windows frames had very low quality.
Another thing. Blast wave is a wave. So it interferes and it's possible that some windows damage was caused by a local overpressure event, which can be result of superposition of waves.
Because lots of damage on the videos are only local in nature (windows are destructed only in some height over ground), I think that guesses in Mt range are exaggerated.

Posted by: Gladstoner Feb 15 2013, 11:34 PM

.

Posted by: Mongo Feb 15 2013, 11:47 PM

http://www.nature.com/news/russian-meteor-largest-in-a-century-1.12438 -- Nature

The impact effects website I have been using says that the energy released during the major explosion, with these numbers, would be around 320 KT. Allowing for shock wave interference effects and shoddy Russian window construction, I suppose the observed damage is possible. Needless to say, it's still one heck of an explosion.

edit -- Since I wrote the above, I learned that:

Posted by: machi Feb 16 2013, 12:19 AM

Needless to say, it's still one heck of an explosion.

Yes it is.
In fact in terms of released energy it's comparable with strategic MIRV warhead.

Posted by: 0101Morpheus Feb 16 2013, 01:09 AM

Needless to say the little unexpected meteor that could stole the show from its bigger sibling that was in the news for almost a year. At the rate new footage is coming out it is going to take days to sort through this.

Police have found a crater in Chebarkul Lake. Probably a fragment that survived the explosion. It seems inevitable that they'll retrieve it but that depends how fast it was still going when it hit the water.

There's a photo of the crater on Phil's blog.

http://www.slate.com/blogs/bad_astronomy/2013/02/15/russian_meteorite_fragment_may_have_fallen_in_frozen_lake.html

Posted by: PaulH51 Feb 16 2013, 02:03 AM

Meanwhile during Sol 187 in the sky above Gale Crater... Another incoming event?

http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/00187/opgs/edr/ncam/NLA_414090313EDR_S0060000NCAM00542M_.JPG

Posted by: nprev Feb 16 2013, 02:39 AM

Who knows? The Tunguska impactor left nary a trace, so it was probably composed largely of volatiles. This thing's composition will be known shortly, and my guess is that it's stony or it would've made a pretty good crater instead of breaking up at altitude.

Posted by: dvandorn Feb 16 2013, 02:54 AM

I've been finger-licking the various videos, and I'm struck by the better views of the actual explosion. There is a flash and a rapid expansion of what looks like a spherical fireball, a very slight dimming, and a second much brighter flash in which the fireball expands enormously. As the fireball quickly dissipates, you see what looks like a very thin cloud of dark smoke that outlines a sphere about the size of the first fireball flash, which itself dissipates (or is drawn into the contrail) in less than a second.

The only lasting effect of the fireball was the thickening of the contrail. But the second flash of the double flash definitely generated a huge fireball that dissipated extremely quickly.

I wonder if the fireball was made entirely of gasses or plasma? Or if any fragmental debris in the fireball was actually pulled back into the contrail by the extreme vacuum created in the wake of the impactor?

I admit, I cheated a little bit in studying the fireball -- I found a youtube video that runs the best angles of the bolide's descent in slow motion:

https://www.youtube.com/watch?v=gW6JVG1SP4c

-the other Doug

Posted by: Bill Harris Feb 16 2013, 03:14 AM

In my work as a hydrogeologist I had occasions to dabble in the (mining) blast effects on structures. One suggestion we saw was that in a tightly sealed building the walls (and windows) would flex more than if the building were not well-sealed in response to an overpressure event. It is Winter and even in a rural area urethane foam weatherstripping is available.

Yes, blast waves can be reflected and interfere constructively or destructively. Take a look at Don Davis' famous painting of the Tunguska event-- it shows blast waves reflecting. And the effects of a blast wave from an atomic explosion reflected off the ground are documented-- see Richard Rhodes' books on the making of the atom bomb.

--Bill

Posted by: Mongo Feb 16 2013, 04:06 AM

NASA has http://www.nasa.gov/mission_pages/asteroids/news/asteroid20130215.html the size of the impactor and explosion:

Posted by: walfy Feb 16 2013, 06:20 AM

It's amazing how today's trail resembles fairly well in some respects (thankfully, not all) the artist's visual approximation of the Tunguska event of 1908.

It would be interesting to see today's trail superimposed along a famous mountain chain, or city, to get an idea of its size. I would do it but I don't know how tall it is, or long.

Considering it's 30, 40? kilometers away in the above photo, it's a massive explosion high up there!

Posted by: Bill Harris Feb 16 2013, 06:52 AM

Another measure of the energy imparted by this event:

--Bill

Posted by: walfy Feb 16 2013, 08:26 AM

According tohttp://attivissimo.blogspot.ch/2013/02/russian-meteor-path-plotted-in-google.html, the main trail, or train, is around 320 km long (200 miles). Here it is superimposed above San Francisco, CA, and a 320 km swath of U.S. coastline, for a perspective.

Another one closer in to the city with a portion of the trail through which the horizon beyond is visible:

Posted by: xflare Feb 16 2013, 09:30 AM

If it exploded/disintegrated that high above the ground, I would say people in the region had a VERY lucky escape. The Tunguska bolide is thought to have exploded 6-10km above ground. If this had done the same, I think we would have had a major disaster.

Posted by: Mongo Feb 16 2013, 01:33 PM

From the science blog http://scienceblogs.com/catdynamics/2013/02/16/impacts/:

Posted by: jgoldader Feb 16 2013, 01:33 PM

Any news yet on the type of the impactor? I saw a couple of pictures of very dark bits in the ice around the hole at the lake, but couldn't tell if the darkness was fusion crust or not. Wondering if it was stony or a chondrite, perhaps something exotic like the Tagish Lake meteorite.

There was a bit on RT.com about divers being called in at the lake. But didn't the Tagish Lake meteorite turn out to be more or less water soluble?

Thanks,
Jeff

Posted by: ElkGroveDan Feb 16 2013, 04:43 PM

This is a good graphic for those of you who do outreach.

Posted by: Mongo Feb 16 2013, 05:04 PM

Interesting graphic, although the impactor is shown as far smaller than it actually was, 2m vs 17m.

Posted by: Paolo Feb 16 2013, 05:47 PM

back to the other asteroid star of the week, has anybody seen any early result of the radar tracking of 2012 DA14?

Posted by: djellison Feb 16 2013, 07:12 PM

As you can see - they're planning to observe it for several days. I'd expect results wouldn't be released until they're finished
http://gssr.jpl.nasa.gov/Calendar/month.php

Posted by: Gladstoner Feb 16 2013, 09:47 PM

.

Posted by: nprev Feb 16 2013, 09:51 PM

That's a good one!

Been trying to figure out the secondaries as well. They don't really sound like echoes, and the local topography seems pretty flat (although the Urals are nearby). My best guess is that they're the shock waves from fragments after the explosion that are still supersonic.

Posted by: Gladstoner Feb 16 2013, 10:01 PM

.

Posted by: dvandorn Feb 16 2013, 10:36 PM

I think the first loud report may have been from the explosion itself. The continuing popping sounds were likely sonic booms created by the remaining relatively large pieces of the impactor as they flew on along the trajectory of the original bolide. The fact that the contrail splits into two distinct contrails for the length of it that was left during the fireball phase of the entry (i.e., when the original object exploded) shows that at least two streams of debris came out of the fireball and recombined into a single, more coherent stream after the fireball faded.

Of course, not all of the debris followed the main stream, lots of pieces big enough to cause sonic booms likely flew out in a multitude of different directions, and many to most of them would still be traveling at supersonic speeds.

-the other Doug

Posted by: Mongo Feb 16 2013, 10:57 PM

All the videos I have seen that continue past the arrival of the main shockwave include a lengthy string of smaller bangs and thumps, some of them quite large in their own right. It seems clear to me that they are the result of secondary explosions as the main meteoroid fragments into smaller and smaller pieces. Unlike a nuclear explosion, a meteoric explosion is not a single event (unless it actually happens at ground level), but a cascading series of increasingly smaller and more numerous events, happening at varying distances from the listener.

Posted by: helvick Feb 16 2013, 11:03 PM

Thunder rumbles aren't generally echoes, just the delayed arrival of the shock wave from points along the strike that are further from you and travelling through fairly chaotic air ( initially at least ).
This should be similar, this thing was hypersonic ( mega sonic?) at 100's of km out, rapidly decelerating to merely supersonic by the time it passed overhead. At 30 km altitude it would have taken about 2 minutes for the shock to reach ground directly beneath the closest point below the main explosion, with earlier shocks gradually catching up, and being increasingly faint over the following minute or two as they caught up. The pops and barrage effect could be just interference along the path but I think its reasonable to assume that there were fragments spalling off and exploding all along the track up to the main fireball providing most of the variation in that recording. The speed of sound is very slow when you are hearing stuff from 30-60 km away, and that looked like a very bumpy ride in to me, even before the main event.

Posted by: Gladstoner Feb 16 2013, 11:38 PM

.

Posted by: Eyesonmars Feb 17 2013, 01:28 AM

I found it interesting that a number of witnesses mentioned feeling the radiant heat of the fireball. A little bigger and we would have had some objects charred on the ground beneath the fireball. How much bigger ?? Even so, the shock wave would have probably extinguished any fires. Much like what happened at Tunguska.

Posted by: nprev Feb 17 2013, 03:22 AM

Do you have any references for the heat perceptions? I would be quite surprised by that given the altitude of the detonation plus slant range(s).

Posted by: Bill Harris Feb 17 2013, 03:25 AM

That is what I had concluded and was going to post here. And remember although the contrail looks like it is just up on the ceiling, it is many miles long and every part of it has a different range in miles and therefore arrival times. And when the object disintegrated, there were thousands of fragments released, each making their own shock wave.

And the videos confirm the conceptual model of the object disintegrating. As it entered ( I keep wanting to say "reentry") it was solid and made a compact plasma sheath perhaps 30 meters diameter. The smoke trail is ablated silicates that have condensed. When the object ruptures it immediately creates thousands of fragments ranging size from boulders to dust, each with it's own aerodynamic characteristics and trajectory and the surface:volume ratio increases rapidly and so does the amount of material being ablated. The plasma sheath rapidly expands due to the unconstrained fragments and the increase in the volume of plasma from vaporized silicates and whatever volatiles were entrained in the rock.

Whew. It's mind-boggling.

--Bill

Posted by: tasp Feb 17 2013, 03:27 AM

I noticed in the different clips shown the degree of camera saturation varied quite a bit. Some of the slower responding imagers totally whited out, and others seemed to have AGC circuits that tried to follow the illumination level.

I was wondering if any photo analysis has been done yet to determine a decel rate along the path for the rock. It would be interesting to have some idea what it withstood before the fragmenting started.

And maybe decel, heating, and turbulence weren't the only effects on it, maybe it was aerodynamically asymmetrical and the slipstream was starting to spin it up some ?

Posted by: Mongo Feb 17 2013, 03:44 AM

I don't have links myself, but I do recall reading reports that mentioned that people felt heat coming through the windows. One person mentioned that curiosity over this unusual heat was what attracted them outside before the shockwave hit. If the fireball was indeed as bright as the sun or brighter, as seems to be the case, then the infrared radiation should be roughly in proportion, so I would not be surprised if there was a short burst of heat when the main explosion happened.

Posted by: Bill Harris Feb 17 2013, 06:04 AM

Do we have any scale information on the cameras used to photograph the Russian bolide? Do we have any idea of the physical dimensions of the dust trail/debris trail (I don't think it's technically a contrail) I've looked at a lot of photographs and videos and I can't get a handle on how to scale the trail. My TLAR sense tells me that it's huge.

--Bill

Posted by: walfy Feb 17 2013, 07:45 AM

Check out this page for its scale: http://attivissimo.blogspot.ch/2013/02/russian-meteor-path-plotted-in-google.html
I attempted to scale it http://www.unmannedspaceflight.com/index.php?showtopic=5524&view=findpost&p=198130.

For what it's worth, I did a quick extraction of 6 sonic boom soundtracks of the meteor from YouTube to see if I could find some similarity between them, at least in the timing of the biggest booms. But nothing stood out as a clear match between any two of them, except for the initial boom, of course! Maybe if a bit more time were spent some similarities could be extracted. But no similarity in the timing and sequence of the booms stands out between any of them with a quick listening or when looking at first 11 seconds of their waveforms:



Of course, there's some glass shattering or car alarms at the beginning of some of them, but some were taken with minimal background noise with the booms standing out. But no pattern. It sounds really different from each location. When all soundtracks play at once, it's a calamity – for the ears!

Something that does stand out is that recordings made closest to the vapor trail almost sound like gunfire or quick and snappy fireworks booms; more distant ones sounded like thunder, "muffled" but still loud.

Posted by: walfy Feb 17 2013, 07:52 AM

ONe more thought for the night: it would be a great study to survey glass breakage under this meteor. I suspect that fewer panes shattered directly below it then to the surrounding immediate vicinity, similar to the trees that still stood under the central blast of Tunguska years ago.

Posted by: FordPrefect Feb 17 2013, 09:41 AM

Some interesting photos on this http://translate.google.com.hk/translate?act=url&hl=en&ie=UTF8&prev=_t&sl=ru&tl=en&u=http://marateaman.livejournal.com/, who just happened to be outside to do nature photography:

http://i55.photobucket.com/albums/g144/berkut_photos/76952_original.jpg

In that photo and the following, it really looks like there are fireball/explosion-like segments visible inside the train still glowing?


http://cs419822.userapi.com/v419822932/2c17/ThbIcy-8wlo.jpg
And an air-to-air image of the train. See the colour variation on the nearer (left) part of the train? It changes from brownish to blueish hues, indications of different materials being vaporized during its "melt off" process?


http://i54.fastpic.ru/big/2013/0215/66/1d6cc8d2b2e95609ad9e4ca3ad9ff066.jpg

Posted by: Paolo Feb 17 2013, 09:42 AM

I had googled that. I was just expecting that, given the media hype, they would be releasing early results in quasi-real time like they did with Toutatis last December

Posted by: ugordan Feb 17 2013, 12:29 PM

This is the explanation I subscribe to as well. Each of those separate fragments would see a significantly different deceleration depending on its ballistic coefficient so the fragment train would quickly spread out in along-track direction, creating all those distinct, subsequent booms.

Posted by: Mongo Feb 17 2013, 01:58 PM

This does not surprise me. Each individual explosion would have happened at a different location in the air, and hence would be a different distance from the listener, with the distance to each explosion varying with the listener's location. A given shock wave would change its time of arrival relative to that produced by a different explosion, even changing from being earlier to being later than the second shock wave, depending on the location of the listener. So the sequence of bangs and booms would be different at each location on the ground.

Posted by: dvandorn Feb 17 2013, 02:48 PM

Exactly the point I made. The multiple booms were sonic booms created by the fragments of the original impactor after the initial explosion.

-the other Doug

Posted by: Bill Harris Feb 17 2013, 02:51 PM

Yes! I noticed those "redder" areas in the initial videos and attributed them to redder light where the blue had been scattered by very small particles (a "sunset effect"). But later-presented and better quality photos do indeed show that the red is incandescent-- I was not expecting the heat to be retained that long, but it's only a very few seconds after the fireball had passed.

--Bill

Posted by: ugordan Feb 17 2013, 02:57 PM

http://www.youtube.com/watch?v=iCawTYPtehk shows nicely that incandescence nicely.

Posted by: Art Martin Feb 17 2013, 05:06 PM

I've seen a number of videos of a flaming crater in the ground but none of them appear on any reputable news stations. Does anyone know the validity of those videos? I don't want to embed the link here because one would think that it would be a prime feature if valid. The hole in the ice images seem to be taken more seriously.

Posted by: Mongo Feb 17 2013, 05:10 PM

Those videos and images of a flaming crater are real, but they have nothing to do with any meteorite impact. Apparently they are of a fire that has been burning mostly underground for years.

Posted by: Art Martin Feb 17 2013, 05:27 PM

I suspected as much, that the people posting them saw an opportunity to get noticed by tagging them onto this event. The edges of the crater are too defined. You'd expect that the ground would be more ragged and the debris splayed out around it if it were a strike. How about the ones of the hole in the ice that seem to be a bit more reported?

Posted by: Explorer1 Feb 17 2013, 06:05 PM

The lake impact is probably authentic, but it might be a while before anything is hauled off the bottom!
Art Martin, I expect any land impact to look kind of like the crater left by the impact in that field in Peru (http://en.wikipedia.org/wiki/Carancas_impact_event); just a big dirty hole, maybe with water filling up the bottom. Plenty of pictures of that one.

Posted by: silylene Feb 17 2013, 06:26 PM

Stefan Geens http://ogleearth.com/2013/02/reconstructing-the-chelyabinsk-meteors-path-with-google-earth-youtube-and-high-school-math/. Shallow grazer!
http://ogleearth.com/wp-content/uploads/2013/02/gif-animation-small1.gif

http://ogleearth.com/wp-content/uploads/2013/02/meteorgeview.jpg

Geen's trajectory can be displayed in this http://ogleearth.com/chelyabinsk-meteor.kmz.

Geen's estimate is that the meteor passed near Chelyanbinsk at 03:15:00 UTC.

Meanwhile there was a 6.8 earthquake in Syagannakh Russia at 08:17:00 UTC. http://www.theregister.co.uk/2013/02/15/shock_meteorite_strike_russia/. Interestingly, and coincidentally, this earthquake lies close to the trajectory path of the meteor (maybe 15 degrees off the path?). Compare Geen's trajectory to the https://maps.google.com/maps?hl=en&safe=off&q=Syagannakh&ie=UTF-8&ei=oQ0hUdizH6PV0gGy-YGwDA&ved=0CAgQ_AUoAg

The quake was 5 hours later however, which make the quake very likely coincidental and nothing more.

If a second meteor had been following the Chelyabinsk meteor, 5 hours later, and impacted near Syagannakh, that would be amazing. Highly unlikely, but it is an uninhabited region, and maybe there were no public reports (one would have to assume if it happened, this putative hit would have lit up the defense grids of both Russia and the US). Still, it might be worth checking if anything unusual happened near Syagannakh (which looks like lake strewn tundra in Google maps).

http://www.theregister.co.uk/2013/02/15/shock_meteorite_strike_russia/
http://regmedia.co.uk/2013/02/15/earthquake640.jpg

Posted by: Bill Harris Feb 17 2013, 06:54 PM

I read about that and it is a well-known burning natural gas methane seep in Russia. After I rolled my eyeballs back down, I looked it up but don't seem to have Bookmarked it. I'll look it up and post more.

That seems to be authentic. I've read that divers have been down and have recovered nothing, yet. I'm sure they'll keep looking-- samples of the impactor will help in determining the dynamics of the event.

Brilliant job of sleuthing!

You can "see" the descending path in the aircraft photo in FordPrefect's images posted in Msg#356.

--Bill

Posted by: Art Martin Feb 17 2013, 06:59 PM

One thing that I've noticed in the cloud the meteor created is that it appears to break up into two pieces early and then those clouds converge into one again as the main explosion occurs which brings up the question, did only one of those pieces explode explaining the remaining fragments that continued to the ground. All I know is the videos are fascinating and those folks were so lucky the thing wasn't just a bit bigger.

Posted by: ugordan Feb 17 2013, 07:37 PM

I have a theory about the twin cloud trail. I'm wondering if it was convection that split it in two. When you have a spherical mass of hot air (like a nuclear fireball), convective movement and resulting vacuum effects quickly produce a rotating toroidal cloud. Maybe what we see here is is what happens with a "cylindrical" fireball? It splits into two, like a cross section of a toroidal cloud?

Posted by: stevesliva Feb 17 2013, 08:33 PM

The depth of the quake ought to be known-- probably not at the surface-- and those folks reporting magnitude estimates from infrasound sensors would probably not forget to mention a second set of booms 5hrs later.

Posted by: ngunn Feb 17 2013, 08:49 PM

Sounds spot on to me. The two halves were too well matched, therefore unlikely to be due to separate objects, so I had already started to wonder if 'double' was 'normal' for these things for some reason. Your explanation fits perfectly.

Posted by: Mongo Feb 17 2013, 08:55 PM

The USGS does report a seismic event that originated a few minutes after the fireball happened, directly under the fireball:



http://www.newsroomamerica.com/story/347587/chelyabinsk_meteor_explosion_caused_magnitude_4_earthquake_.html

Posted by: Bill Harris Feb 17 2013, 09:50 PM

The video that I saw in another site has been removed by the user, but I applied my Google-Fu and found that it is a burning natural gas seep in Derweze (Darvaza) Turkmenistan known as "The Door to Hell". Google "door to hell derweze turkmenistan" for more info than we all need to know...

Wiki link at: http://en.wikipedia.org/wiki/Door_to_Hell which mentions "A short video of the Door to Hell has been circulating on the internet, falsely identified as the impact site for the 2013 Russian meteor event."

--Bill

Posted by: walfy Feb 17 2013, 10:10 PM

I don't know if this has been discussed yet, and maybe don't understand this well enough, but the succession of booms heard from the ground might have been in reverse order for most locations where it was heard. Especially directly under the main trail. The meteor came punching into the atmosphere well beyond the speed of sound, so all propagating explosions and shock waves could not keep up with the front of the train. Let's say you were standing directly below that main explosion that remained incendiary for a few seconds. The shock wave from that would hit you first. What about all the other smaller shock waves preceding it? They would then strike your ears in succession, but in reverse order than actual time of origination.

The series of booms heard is the actual sound of the meteor's entry, but played out in reverse! For example, the first explosion of the meteor itself was the highest up there, and so will reach the ground last, since the train is moving much faster than speed of sound.

This illustration comes to mind: Imaging being in a hot air balloon above a lake and spraying a machine gun in a direct line from one shore of the lake to the opposite shore. The waves from the last bullet shot will wash ashore first on that opposite side of lake, followed by the rest of them in reverse order. The first bullet fired will have hit that far shore last.

Maybe there's something completely fundamental I'm overlooking. the idea seems too strange...

Posted by: AndyG Feb 17 2013, 10:43 PM

That's the way (and why) nearby lightning strikes rumble on: you hear the closest part of the near-instant flash first, followed by more distant sound "catching up".

Andy

Posted by: Bill Harris Feb 18 2013, 04:24 AM

I've been doing some reading and the closest "terrestrial" analog to the dust trail left by the Russian bolide is a nuee ardente (literally, "glowing cloud") pyroclastic flow, at least the lighter airborne fraction and not the ground-hugging surge:

A quickie Google link on this is: http://www.google.com/search?q=nuee+ardente

As the meteorite disintegrated and ablated it became, literally, a plasma of vaporized basalt plus volatiles and gasses which immediately started to condense into a basaltic (volcanic) ash with very hot gasses which was quite buoyant and made the observed cauliflower clouds along the trail. Parts of the cauliflower puffs were still incandescent (literally seconds after formation), which sets a range of temperatures. I've been looking at a lot of images of the "nuee ardente" flows but haven't seen any that are still glowing (not a surprise, we're seeing a volcanic eruption late on the game).

This event is going to make for a some great papers at next year's LPSC...

--Bill

Posted by: pandaneko Feb 18 2013, 08:46 AM

I have not read all of the previously uploaded contributions, so my apologies, in advance, if I am duplicating similar articles again.

Not this one, of course, but let us say, some of the future incoming bodies like this are rotating in their own frame of reference what do we do then?

People talk about painting these asteroids, or attaching ion engines to them in the hope of deflecting their orbits in the long run. Can we do that when they are rotating around their own axis?

Pandaneko

Posted by: AndyG Feb 18 2013, 10:21 AM

Rotation helps for larger asteroids of a rubble-pile, gravitationally-bound, construction. Painting an asteroid black would result in the warmed surface emitting IR to a higher degree during the "dusk" side of rotation compared to the "dawn" side. Given time an orbit could be adjusted.

The problem with smaller objects, such as this Russian one - presuming they're solid rock chunks - is that the rotation rate could well be significantly above that of a gravitationally-bound body, reducing the benefit of paint.

Rotation. Hmmm. Just a thought to Art and ugordan - do the twin trails seen here reflect the equivalent of "tip vortices" generated by the lift of a rotating body?

Andy

Posted by: remcook Feb 18 2013, 03:04 PM

Apparently, fragments have now been found http://en.ria.ru/russia/20130217/179531203/Meteorite-Fragments-Found-in-Icy-Urals-Lake---Scientists.html

Posted by: Bill Harris Feb 18 2013, 04:20 PM

Yep, "fragments found" and now we're going to see the squirrels come out of the woodwork with eBay sales.

"Meteorite rush" begins as Russian scientists find fragments
http://news.yahoo.com/meteorite-rush-begins-russian-scientists-fragments-111415119.html;_ylt=Ap3erj3NGsgK4yufsmWsQVWs0NUE;_ylu=X3oDMTNsOHRscnJvBG1pdANUb3BTdG9yeSBGUARwa2cDYTliZTIxNDUtZDViNi0zYWFmLWE4MTktMzgwZWU2N2ZiNDUyBHBvcwM1BHNlYwN0b3Bfc3RvcnkEdmVyAzk1ODIwMmUzLTc5YzUtMTFlMi1iZjczLWFmOWUyMTA5NTJkYw--;_ylg=X3oDMTIwNjVsc3ZuBGludGwDdXMEbGFuZwNlbi11cwRwc3RhaWQDBHBzdGNhdANob21lBHB0A3NlY3Rpb25zBHRlc3QDVGVzdF9BRkM-;_ylv=3

But it is good that (actual) fragments are turning up. It gives an idea of the composition, and therefore the type of asteroid and the structure and a better understanding of the dynamics of the breakup. From the Russian scientists involved, "These are classified as ordinary chondrites, or stony meteorites, with an iron content of about 10 percent..."

I liked this comment:

This is not surprising. When the object disintegrated it didn't completely flash into plasma. No doubt many small fragments were decelerated quickly and fell along the flight path in a ballistic trajectory. I look at the object as being converted into a flying gravel pile-- even if only 1/10 of 1% survived, that is a lot of meteorites!

--Bill

Posted by: dvandorn Feb 18 2013, 06:43 PM

There is likely a rather large "strewn field" where fragments of the meteor landed. I wonder if the Discovery Channel is in negotiation to film a segment or two of the series "Meteorite Men" in Siberia?

-the other Doug

Posted by: stevesliva Feb 18 2013, 07:50 PM

Chelyabinsk isn't in Siberia, though, right? This is too far south to be siberian.

Posted by: Explorer1 Feb 18 2013, 08:07 PM

The boundaries and definitions are rather fuzzy; in terms of federal districts, its actually part of it. If Siberia is defined as east of the Urals than yes. Scroll down here to see Chelyabinsk listed: http://en.wikipedia.org/wiki/Siberia#Borders_and_administrative_division

Posted by: Pertinax Feb 18 2013, 09:25 PM

What kind of confidence is reasonable with the infrasound estimates of the airburst? On a similar note, does anyone have a cold-war era air-burst calculator (such as http://calculating.wordpress.com/2012/05/08/air-burst-effects-computer-no-1/) to see what effects a 500kT explosion at ~85,000ft would have at various ranges?

Part of my reason for asking is that given the approximations from Collins et al (http://impact.ese.ic.ac.uk/ImpactEffects/effects.pdf), a larger blast seems necessary to produce the observed ground effects (assuming I am not making some bonehead mistake(s), which might not be a safe assumption ).

Using the most recent published numbers, I get:
http://impact.ese.ic.ac.uk/cgi-bin/crater.cgi?dist=27.5&distanceUnits=2&diam=17&diameterUnits=1&pdens=2770&pdens_select=3000&vel=20.6&velocityUnits=1&theta=22.5&wdepth=&wdepthUnits=1&tdens=2500

... while the following seems to reproduce the knows better (using http://ogleearth.com/2013/02/reconstructing-the-chelyabinsk-meteors-path-with-google-earth-youtube-and-high-school-math/ and http://www.youtube.com/watch?v=gQ6Pa5Pv_io&feature=player_embedded as references):

http://impact.ese.ic.ac.uk/cgi-bin/crater.cgi?dist=34&distanceUnits=1&diam=30&diameterUnits=1&pdens=2500&pdens_select=3000&vel=25&velocityUnits=1&theta=22.5&wdepth=&wdepthUnits=1&tdens=2500


Thoughts?


-- Pertinax

Posted by: Mongo Feb 18 2013, 10:19 PM

One thing I have found is that "distance from impact" in that program means "horizontal ground distance from directly under the explosion". If you enter 0.1 km instead of 44.3 km, the results are much closer to the expected numbers, especially if you use the revised density of 3957 kg/m^3 to give a mass of 10,000t, and a velocity of 32.5 km/s to produce an energy release of 500 kilotons, with an 89s travel time for the shock wave to reach the ground.

Posted by: ugordan Feb 18 2013, 11:45 PM

There's a piece of software that runs in DOS and it uses models based on empirical data, but I don't think it would have produced meaningful overpressure values at those airburst altitudes since the data it was fed was based on much lower airburst data, typical of altitudes a weapon would effectively be used in combat, not 27 km.

Posted by: ugordan Feb 18 2013, 11:47 PM

I thought the entry velocity was estimated to be around 18 km/s?

Posted by: nprev Feb 19 2013, 12:12 AM

I think they said 18 miles per second, G, which converts to around 28 km/s. (Sorry; that probably doesn't help, does it?)

Posted by: ugordan Feb 19 2013, 12:21 AM

Hmmm, http://www.nasa.gov/mission_pages/asteroids/news/asteroid20130215.html says "about 40,000 mph (18 kilometers per second)"? Also, this http://blogs.nasa.gov/cm/blog/Watch%20the%20Skies/posts/post_1361037562855.html (if it shows a prograde orbit) looks too inner-solar-system to me for something coming in at 28 km/s.

Posted by: Mongo Feb 19 2013, 12:39 AM

Using that http://impact.ese.ic.ac.uk/cgi-bin/crater.cgi?dist=0.1&distanceUnits=1&diam=24.5&diameterUnits=1&pdens=4000&pdens_select=0&vel=18&velocityUnits=1&theta=12.5&wdepth=&wdepthUnits=1&tdens=2500, I find that to get the correct fireball energy release (500 kilotons) and shock wave time delay (89 seconds) using an entry velocity of 18 km/s with an impact angle of 12.5 degrees, I need to assume a meteoroid initial diameter of 24.5m with a density of 4,000 kg/m^3 and a mass of 30,800 tonnes.

Posted by: Pertinax Feb 19 2013, 02:24 AM

Thank you all for the tips and comments thus far.

It may just be that the impact calculator is not well suited for events such as this. I will brush up on it tomorrow. In the mean time, in my second scenario I tried to constrain the simulation as best I could to the physical knows, such as distance of the observer to the explosion (hypotenuse) and its companion shock wave delay and blast effects, ballpark density of the stony meteor, and very roughy estimate for a rather shallow entry into the atmosphere.

It it a fun puzzle.

Pertinax

Posted by: Bill Harris Feb 19 2013, 02:32 AM

To pick Nits: I'm thinking that the calculations for energies of air-burst explosions or ground impacts make the assumption of instantaneous point-source releases. In the case of an object entering the atmosphere the energy is created and dissipated over several seconds and several miles. Think of it as a difference between one ounce of flash powder ignited in a confined space or ignited in a line 5 feet long. The difference between a BANG and a whooosh. The total energy is the same but the temporal distribution is different.

--Bill





EDIT-- yes, temporal AND spatial. That is what I was thinking since it was moving. But I didn't write it down.

Posted by: silylene Feb 19 2013, 12:48 PM

That is correct. Another key distinction is not only is the temporal distribution different than a point source explosion, the spatial distribution is also different. The energy release of a meteor entering the atmosphere and vaporizing into a plasma pancake streaming across the sky is spread across both time and distance. A nuclear explosion energy release can be considered to be a point source in both time and distance to a close approximation.

Posted by: Mongo Feb 19 2013, 09:21 PM

That only makes things worse, though. I was already having difficulty reconciling the stated explosion energy from NASA (500 kilotons) with the observed shock wave effects in the videos given the distance from the energy release (several megatons, according to the impact effects calculator). Having the overpressure effects due to a meteor airburst be extended in time due to its spatial and temporal extent reduces the expected overpressure even further.

Could it be that as the infrasonic network is designed to detect nuclear detonations (which are as you suggest point-like sources in both time and space), that the algorithms used are unable to properly estimate yields for the much more extended meteor events? I really do think it probable that the actual energy release was several times the "official" figure from NASA.

Posted by: silylene Feb 19 2013, 09:32 PM

Mongo, I tried to to model the Chelyabinsk impact on the first days (another forum). I could only get slightly reasonable results in terms of airburst height and damage if I assumed the impactor to be composed of pure iron, or even denser.

Posted by: ugordan Feb 19 2013, 10:02 PM

What are you basing this probability on?

Posted by: Mongo Feb 19 2013, 10:05 PM

There is definitely something wrong with the numbers we have been given (assuming that the impacts effect calculator is reasonably accurate).

The observed shock wave effects strongly suggest a ground-level overpressure of at least 1 kPa. Allowing for other influences such as constructive interference and bad construction might reduce this to 0.5 kPa, but that is lowering the overpressure to the limits of plausibility.

We know that the transit time between the explosion and the arrival of the shockwave, directly under the blast, is just under 1.5 minutes.

We are told that the meteor was traveling at around 18 km/s.

From looking at the videos, the meteor was traveling at a very shallow angle to the ground, under 15 degrees.

We are told that the recovered meteorite fragments are chondritic with about 10% iron, for a density of around 4000 kg/m^3.

Putting the speed, trajectory angle and density into the http://impact.ese.ic.ac.uk/ImpactEffects/, and adjusting the other parameters to get a 1.5 minute shockwave transit time and 0.5 kPa overpressure at ground level, results in the following (there is a range of possible diameters and trajectory angles, but they all produce the same size of explosion).

Your Inputs:
Distance from Impact: 100.00 meters ( = 328.00 feet )
Projectile diameter: 38.50 meters ( = 126.00 feet )
Projectile Density: 4000 kg/m3
Impact Velocity: 18.00 km per second ( = 11.20 miles per second )
Impact Angle: 7.5 degrees

Energy:
Energy before atmospheric entry: 1.94 x 1016 Joules = 4.63 MegaTons TNT
The average interval between impacts of this size somewhere on Earth is 550.4 years

Major Global Changes:
The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).
The impact does not shift the Earth's orbit noticeably.

Atmospheric Entry:
The projectile begins to breakup at an altitude of 45200 meters = 148000 ft
The projectile bursts into a cloud of fragments at an altitude of 29700 meters = 97300 ft
The residual velocity of the projectile fragments after the burst is 13.9 km/s = 8.61 miles/s
The energy of the airburst is 7.87 x 1015 Joules = 1.88 MegaTons.
No crater is formed, although large fragments may strike the surface.

Air Blast:
The air blast will arrive approximately 1.5 minutes after impact.
Peak Overpressure: 509 Pa = 0.00509 bars = 0.0723 psi
Max wind velocity: 1.2 m/s = 2.68 mph
Sound Intensity: 54 dB (Loud as heavy traffic)

Posted by: Mongo Feb 19 2013, 10:17 PM

The observed breakage effects. The extent of broken windows and the observed damage to window frames strongly implies an overpressure of around 1 kPa. Even allowing for interference effects and poor construction, I doubt that the overpressure could be less than 0.5 kPa, and that is pushing it in my opinion. The size of explosion needed to produce the inferred overpressures, at the calculated distance going by shockwave travel time, is several times the stated 500 kilotons.

It seems probable that a larger proportion of the total energy release went into shockwave production, instead of radiation and the visible/thermal flash, but even in a conventional fusion device, around half of the total energy goes into the shockwave, and we know that a substantial fraction of the Chelyabinsk explosion energy was in the form of visible and thermal radiation (many reports of a wave of heat, and the fireball being "brighter than the sun"). Even if 90% of the energy release was contained in the shockwave, 500 kilotons seems much too small to account for the observed damage.

Posted by: dvandorn Feb 19 2013, 10:35 PM

Remember that the blast wave from the main explosion does not immediately lose its momentum. It's still screaming towards the ground at supersonic speed. The momentum of the original impactor added to the blast wave would enhance the blast effects at the point where the wave is most directly pointed at the ground.

A lot of the models of mid-air explosions of great strength (i.e., nuclear explosions) have the fatal flaw of assuming the explosion occurs from, and expands outwards from, a single fixed, unmoving point. This is not the case when a meteor plowing in at hypersonic speeds explodes. Some analyses of the Tunguska event are now downgrading the actual size of that explosion after the effects of the momentum of the blast wave were taken into account.

-the other Doug

Posted by: Pele's Planet Feb 20 2013, 12:33 AM

I read today that scientists from Urals State University analyzed 53 meteorite fragments (0.5-1.0 cm in size) and concluded it was an ordinary chondrite. Looks like an L-group since the iron content was only ~10%. The interview with one of the scientists also indicated it had olivine and sulfite. I was curious if the "sulfite" could be a sulfide such as troilite. I looked for information on sulfite in meteorites, but only came up with sulfides. That, combined with the fact that he used chrysolite (a less commonly-used term for olivine) made me curious if a language/reporting barrier was at work. Does anyone have more information on the meteorite composition?

Posted by: Bill Harris Feb 20 2013, 01:12 AM

This is all new ground. We have empirical and observed data that gives the air overpressure (and energy) of a explosive airblast and can transfer much of that to an entering hypervelocity body that disrupts. But these models are a WAG based on what we've seen, but we've not seen an impactor of this magnitude ever. We need to start with the observed data (that Holy Grail ! ) and see what assumptions need ot be applied to make the model output fit the observed.

The only comment I would have on Mongo's data input is the "Projectile Density" of 4000 kg/m3 (which I make to be 4.00 gm/cm3). A chondrite typically has a density (specific gravity) of 3.0-3.7 gm/cm3, so I'd assume a density of 3.3 gm/cm3.

I'd like to look under the hood of that impact model and see what makes it tick.

--Bill





Very good, Mike (lifting bonnet as we speak)
\/ \/ \/

Posted by: mcaplinger Feb 20 2013, 03:55 AM

http://impact.ese.ic.ac.uk/ImpactEffects/effects.pdf is a very thorough discussion of the model.

Posted by: JRehling Feb 20 2013, 04:17 AM

It seems to me that one unknowable quantity is the structural integrity of the object before breakup, which would determine how much force was required to generate the breakup, which would determine the altitude of the breakup. The shape of the object, and thus how aerodynamic it was, would also govern how much force was generated as a function of altitude. And once air resistance initiated tumbling, etc., more unknowns.

I remember from the John Hershey book that the Hiroshima explosion was heard at certain distances from ground zero but not at certain closer distances, which may have owed to orographic effects that would not apply with the much higher altitude of the Chelyabinsk event, but it suggests that counterintuitive nonmonotonicities may exist regarding sound as a source of information regarding explosions.

At the very least, it seems that the unknowns regarding structural integrity introduce significant uncertainty regarding every other aspect of the event. I don't see how those can ever be accounted for, although we might make any number of assumptions and proceed to model the event contingent on those assumptions. It seems to me that the unaccounted-for variation is likely vast.

Posted by: Mongo Feb 20 2013, 04:36 AM

This might be of interest. I checked the output of that impact effects calculator for a range of trajectory angles for the same meteoroid that produces a 500 kiloton explosion at the correct height for a 15 degree trajectory, and with a density of 3300 kg/m^3 as per Bill Harris. (It still requires a much larger meteoroid than NASA's estimate).

Your Inputs:
Distance from Impact: 100.00 meters ( = 328.00 feet )
Projectile diameter: 26.00 meters ( = 85.30 feet )
Projectile Density: 3300 kg/m3
Impact Velocity: 18.00 km per second ( = 11.20 miles per second )

Impact Angle: 15 degrees
The projectile bursts into a cloud of fragments at an altitude of 29600 meters = 97000 ft
The energy of the airburst is 0.50 MegaTons.
The air blast will arrive approximately 1.49 minutes after impact.
Peak Overpressure: 162 Pa

Impact Angle: 30 degrees
The projectile bursts into a cloud of fragments at an altitude of 21100 meters = 69200 ft
The energy of the airburst is 0.70 MegaTons.
The air blast will arrive approximately 1.06 minutes after impact.
Peak Overpressure: 524 Pa

Impact Angle: 45 degrees
The projectile bursts into a cloud of fragments at an altitude of 16200 meters = 53300 ft
The energy of the airburst is 0.82 MegaTons.
The air blast will arrive approximately 49.2 seconds after impact.
Peak Overpressure: 1190 Pa

Impact Angle: 60 degrees
The projectile bursts into a cloud of fragments at an altitude of 13300 meters = 43700 ft
The energy of the airburst is 0.90 MegaTons.
The air blast will arrive approximately 40.3 seconds after impact.
Peak Overpressure: 2150 Pa

Impact Angle: 75 degrees
The projectile bursts into a cloud of fragments at an altitude of 11700 meters = 38400 ft
The energy of the airburst is 0.93 MegaTons.
The air blast will arrive approximately 35.5 seconds after impact.
Peak Overpressure: 3100 Pa

Impact Angle: 90 degrees
The projectile bursts into a cloud of fragments at an altitude of 11200 meters = 36800 ft
The energy of the airburst is 0.95 MegaTons.
The air blast will arrive approximately 34 seconds after impact.
Peak Overpressure: 3520 Pa

Posted by: Bill Harris Feb 20 2013, 10:44 AM

Yes, those and the other variables could throw any model into a tizzy. The impactor could be anything from a flying rubble pile to a solid chunk of basalt.

Mercy, that is a beautiful word.

--Bill

Posted by: ElkGroveDan Feb 20 2013, 03:07 PM

Now that someone has calculated an orbit, it would be interesting to see if it can be spotted in any old imagery. I know it's a long shot, but it was definitely larger than bodies that have been observed previously.
http://en.wikipedia.org/wiki/2008_TC3 http://www.nature.com/nature/journal/v354/n6351/abs/354287a0.html http://www.space.com/615-small-asteroid-passes-satellites-earth.html http://www.birtwhistle.org/2003SQ222/Universe_Today_Small_Asteroid_Came_Very_Close.htm

Posted by: ugordan Feb 20 2013, 04:44 PM

Considering that the worked-out orbital parameters are bound to be highly uncertain, I'd say looking for it in past imagery would be a futile effort. It came in from the sunward direction, that means it was only visible in night skies a good while ago and the positional uncertainty calculated for that epoch would be huge, I guess.

Posted by: Holder of the Two Leashes Feb 20 2013, 09:08 PM

I agree. The odds of it having been spotted in the past are very small anyway. Asteroids the size of this meteor have an absolute magnitude in the range of 26 to 28, depending on how bright the material. For the best modern surveys like Pan-STARRS, the rock has to be within 0.1 AU of earth if it is abs mag 26, and within 0.05 AU if it is 28, in order be picked up. Even then you have to get lucky, with it favorably placed with a low phase angle.

Only a small fraction of earth crossers this size have been spotted. Even fewer with enough observations to get a rough orbit plotted. Then most of those are lost and never seen again. A check of the MPC database shows that about 890 near earth asteroids have had their orbits plotted that are as dim or dimmer than this meteor was likely to be. Six of those so far have been spotted on a subsequent pass (or opposition) near the earth. None of them have been located on archived data from a previous pass that was prior to their discovery.

For comparison, so far they've found about 25% of the asteroids that would currently be classified as "potentially hazardous", which have to have absolute magnitudes at least as bright as 22, a hundred times brighter than mag 27.

True, but the meteor may have immortalized 2012 DA14, at least as a side note. Possible future quote:

" ... on that day, astronomers were focused on another small asteroid, 2012 DA14, which by an incredible coincidence happened to be in the neighborhood at the same time..."

Posted by: Mongo Feb 22 2013, 04:07 AM

http://xxx.lanl.gov/abs/1302.5377

Posted by: centsworth_II Feb 26 2013, 09:29 PM

http://m.youtube.com/#/watch?v=t5DgXLbjaQQ

Video linked from orbit reconstruction study in previous post.

Posted by: Greenish Mar 3 2013, 03:35 AM

A substantial writeup at http://neo.jpl.nasa.gov/news/fireball_130301.html
Don Yeomans & Paul Chodas, Additional Details on the Large Fireball Event over Russia on Feb. 15, 2013 NASA/JPL Near-Earth Object Program Office March 1, 2013

Posted by: Bill Harris Mar 4 2013, 09:00 PM

Thanks-- that confirms a lot of the speculation that we were tossing around last month.

--Bill

Posted by: Mongo Mar 8 2013, 04:55 AM

http://xxx.lanl.gov/abs/1303.1796

Posted by: ElkGroveDan Mar 8 2013, 05:48 AM

As are all the other sides. Perhaps the authors meant, "This side is totally unmonitored."

Posted by: dvandorn Mar 8 2013, 04:30 PM

I find it interesting that in the histories of the development of the Saturn V rocket, a big deal is always made of the fact that if the rocket were to ever explode on the launch pad, it would result in a blast the size of a "fair-sized nuclear weapon." However, the yield estimate for an exploding Saturn V was given as between 3 and 5 kilotons.

So, to put it into perspective, this meteor exploded in a blast roughly 100 times more powerful than an exploding Saturn V rocket...

-the other Doug

Posted by: ugordan Mar 8 2013, 05:03 PM

Yes, but it exploded about 10 times farther away from any observers than an on-pad Saturn V explosion would have. Shockwave overpressure IIRC roughly drops off as the inverse cube of distance so they're kind of in the same ballpark, especially if you consider that the 5 kT estimate for Saturn V is pretty generous.

Posted by: Mongo Mar 8 2013, 08:59 PM

The http://impact.ese.ic.ac.uk/ImpactEffects/ requires a diameter of 26.5m and density of 3100 kg/m^3 to be input in order to produce http://impact.ese.ic.ac.uk/cgi-bin/crater.cgi?dist=0.1&distanceUnits=1&diam=26.5&diameterUnits=1&pdens=3100&pdens_select=0&vel=16.7&velocityUnits=1&theta=15.8&wdepth=&wdepthUnits=1&tdens=2500 (entry velocity 16.7 km/s, trajectory 15.8 degrees from horizontal, airburst energy 440 kt, shock wave travel time 1.48 minutes). This yields a mass of 30 thousand tonnes for the object.

Of course the results are only as accurate as the underlying physics model of the simulation.

Posted by: mchan Mar 9 2013, 06:52 AM

Perhas the authors meant, "This side is totally unshielded from the sun."

Posted by: silylene Mar 10 2013, 07:41 PM

That brought to mind the Feb. 15 1996 low altitude explosion of the Long March rocket over China (which is a lot less explosive power than a Saturn 5). Video in this link, the blast damage to the occupied buildings and homes on the ground was horific. http://www.abovetopsecret.com/forum/thread748857/pg1.

Posted by: Holder of the Two Leashes Aug 5 2013, 03:02 PM

The meteor may have been a member of a hypothetical family of asteroids with 2011 EO40 as the parent of the group.

http://www.spacedaily.com/reports/Asteroid_named_as_possible_source_of_exploding_Russian_meteorite_999.html

http://arxiv.org/abs/1307.7918

http://www.spacedaily.com/reports/Chelyabinsk_meteorite_may_have_gang_of_siblings_999.html

Posted by: Mongo Aug 9 2013, 07:53 PM

The author argues that the NASA estimate of 500 kilotons for the Chelyabinsk explosion is far too low, and in fact physically impossible (an explosion of that size, at that altitude would produce an atmospheric shock wave that would be too small to be able to produce the observed damage, by a factor of around a hundred). He also states that the size estimate using measured flash energy is calibrated only up to a 1 kt explosion, and fails for the (4-5 orders of magnitude larger) Chelyabinsk explosion. He also proposes that the Chelyabinsk and Tunguska objects were originally part of the same comet.

http://arxiv.org/abs/1307.1967

As is known, in the morning February 15, 2013 at about 9:20:30 local time, an explosion of some object which was moving along a gently sloping trajectory with a very high speed was at considerable height in the vicinity of Chelyabinsk near the point at approximately 54.85° north latitude and 61.20° east longitude. This point is located approximately 35 kilometers south-south-west of the center of Chelyabinsk, at which was accepted Lenin Square. This object is now called Chelyabinsk (Russian) meteorite or meteoroid [2]. There was early winter morning, and solar time at the epicenter of the explosion was 7:25:20.

On the vast territory stretching between Zlatoust – the city to the west of Chelyabinsk, Troitsk – the city to the south and Miassky – the village in the northeast, were fixed damage to buildings, broken windows and doors [3]. Total 1,613 injured persons were in the incident, most of them – because of the knocked-out windows. Hospitalization was subjected to different data from 40 to 112 people; two victims were placed in intensive care. Such amount of persons affected by falling of the object from space in historic times has not yet been registered [2]. Distance from the epicenter of the explosion up to the extreme points of the destruction zone exceeds 70 km away at least, and Zlatoust and Troitsk are located at the distance at least 90 km. This means that pressure generated by the shock wave from the explosion at a distance of 90 km from the epicenter, was about 5 kPa (kilopascals), what immediately indicates the explosive energy of tens of TNT megatons (for details, this thesis is described in the section IV of this article.)

Not far from the epicenter of the explosion is the city Korkino, at the market of which, at latitude 54.89° north and 61.40° east longitude, at the distance from 13.5 to 14.5 km from the epicenter was filmed very important video [4]. Delay (on this video) of the explosion sound from the flare was 89.5 seconds, and with taking into account the temperature distribution of atmosphere [5] and speeding the explosion wave over the sound [6], it was determined that the slant range to the explosion center was 28.9 km. By movement of the shade from the vertically standing mast on the video, it was concluded that the shadow of mast strived for 0.55 of its altitude in the moment of the flare, resulting in a height of the explosion was 25 – 25.5 km.

******

The kinetic energy of the input has minimum at rp ≈ 0.80, the energy of the explosion remains almost unchanged and its value is approximately equal to 58 megatons of TNT. When height of explosion is 25.0 km trends are similar, mass of the object are the same, but density is higher at 110 – 130 kg/m3, and diameters, respectively, less on 8 – 10 meters. The energy of explosion does not change for different rp and is of about to 56.5 Mt. Thus, the energy of the explosion in the sky in Chelyabinsk was almost equal to the energy of the most powerful thermonuclear explosion of so-called Tsar bomb, performed by the Soviet Union of 30 October, 1961 on the New Earth.

However the effect of explosion of Chelyabinsk object on the ground was not so catastrophic due to the high altitude. [...] Even in the epicenter peak overpressure on the wave could not reach 15 kPa, at the distance of 35 km (roughly in the center of Chelyabinsk), he was already below 10 kPa. Peak overpressure 5 kPa at a distance of 90 km is a boundary condition for the solution of this problem. When a height of explosion is 25.0 km, excess of the peak overpressure in the epicenter would be 0.4 – 0.5 kPa, at 20 km distance – near than 0.3 kPa, and then they would almost compared with the values that are presented in Table 3. The wave with a peak overpressure 5 kilopascals on a flat terrain without shielding by buildings knocks out the windows enough with confidence, at 10 – 15 kPa may be damaged and weak destruction of multi-storey buildings.

******

The major differences between the characteristics of Tunguska and Chelyabinsk objects are: almost twice smaller diameter of the first than of the second, in the 5.5 – 6 times less mass and a 4 – 4.5 times less energy of the explosion. However, the peak overpressure of the shock wave at the epicenter of Tunguska explosion is 7 times higher than in the epicenter of Chelyabinsk explosion because of a difference a factor of 3.5 in the heights of these explosions. Next, when the distance from the epicenter increases, a gradual rapprochement between the parameters of two explosions occurs and pressure peaks become equal at a distance of approximately 40 km from the epicenter. At greater distances, much more powerful and more high-rise Chelyabinsk explosion produces more powerful wave.

******

Thus, in the morning February 15, 2013 the fragment of comet has exploded in the sky over Chelyabinsk at a height of 25.5 km. Its size was of approximately 195 m, density – of about 500 kg/m3 and mass – of about 1.95 Mt. Energy of the explosion was 58 megatons of TNT. Over 104.5 years before this, June 30, 1908 the fragment of the same comet has exploded on the Stony Tunguska, that was much smaller, however, it is still considered the largest celestial body that entered the Earth atmosphere in historic times. Because of unity of origin, it had the same density, but its minimum size was 115 m, and mass – 0.40 Mt. The energy of explosion was about 14.5 Mt, but because of that the height at which this incident has occurred, was 7.7 km, the impact on the underlying surface at that time was not an example of a stronger. The calculated data of Tunguska incident are in excellent agreement with those previously obtained by several generations of researchers for decades of work on this problem: the energy of the explosion from 7 to 17 Mt at the altitude of between 6.5 and 10.5 km.

It should be noted, however, that the results by Chelyabinsk object are in sharp contrast to those which have been replicated around the world by the media with links to NASA immediately after the incident. The first release from NASA February 15, 2013 reported that Chelyabinsk meteor had size before entering the atmosphere 15 m, mass – 7 kilotons, flight speed was 18 km/s, and energy of explosion was «hundreds kilotons» of TNT. The bases of these estimates have not been specified. Later in the same day a clarification was followed that the size of the object is increased to 17 m, mass – up to 10 kilotons, and the estimate of the explosion energy has grown for some reason already from «30 kilotons » to 500 kilotons of TNT. The arguments for the new estimates are follows: the data «had been collected by five «additional» infrasound stations located around the world – the first recording of the event being in Alaska».

Given that a half of the second degree of the object speed multiplied at the stated mass, and divided the result by 4.18 MJ/kg (specific energy of TNT), any other men than the authors of this release should to receive no more than 390 kilotons of TNT but not 500, it can be concluded that they were in such a hurry that forgot even the law of conservation of energy. In addition, the staff of JPL should to know that energy of final explosion of such small objects is much lower than their initial kinetic energy during the input into the atmosphere as a result of energy dissipation on the trajectory. In this particular case, the calculations lead only to 120 kilotons of explosive energy. With this explosion peak pressure of the shock wave in Chelyabinsk would be, at least in the more than 300 times lower than observed, and there would be absolutely no damage there.

Obviously, the size of the object could not be determined only with the aid of infrasound stations which record perturbations in the atmosphere. Confusion with the data on energy shows that the size of the object could not have been defined through theirs. This leads only to a single logically valid option – the authors of release have determined the size of Chelyabinsk object as maximum of that they cannot detectable in the near-Earth space with modern automated optical tracking system. It was soon confirmed by the «scientific justification» of this approach. However, none of them have thought that circumsolar angles are not accessible to these systems, but this fragment have flown so – it direction of input was rejected on the direction on the Sun at an angle of about 13.6° (for the ChO-5 variant), see also section IV and/or memorandum.

Moreover, soon there were the «additional confirmation» of this erroneous from any point of view of an assessment of explosion energy of the Chelyabinsk object – 500 kilotons. There have been received these notorious 500 kilotons through correlation between energy of flash light and energy of the explosion. However this correlation was made only for one parameter and for energy range of explosions was 0.1 – 1 kilotons. In reality there were big divergences between empirical points and the correlation curve because of influence of many parameters.

Posted by: Paolo Oct 16 2013, 05:25 PM

I large chunk of the Chelyabinsk meteorite has been recovered from the floor of lake Chebarkul
http://rt.com/news/largest-fragment-meteorite-lifted-258/
I wonder how good is the meteorite now for scientific analyses after spending 8 months under water...

Posted by: Paolo Nov 6 2013, 07:09 PM

a few new papers on the Chelyabinsk meteor.
in Nature:
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12671.html?WT.ec_id=NATURE-20131107
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12741.html?WT.ec_id=NATURE-20131107

and two special issues (currently in free access) of Solar System Research:
http://link.springer.com/journal/11208/47/4/page/1
http://link.springer.com/journal/11476/51/7/page/1

Posted by: Paolo Nov 7 2013, 08:08 PM

...and in Science too: http://www.sciencemag.org/content/early/2013/11/06/science.1242642

Posted by: ChrisC Nov 12 2013, 03:28 AM

... which leads also to their weekly podcast, where one of the authors discusses this at length:

http://www.sciencemag.org/content/342/6159/753.2.full