APOD: Asteroid 2012 DA14 Passes the Earth (2013 Feb 17)

[Chris Peterson]

Too soon to know if any pieces of the " Ural rock " been picked up yet ? During one of the videos I heard a loud crashing sound.

There appear to be credible reports that at least a few small pieces have been recovered. The appear stony, probably chondritic.

All of the noise was from atmospheric shockwaves, not falling material.

[neufer]

<<As attested by Sigismund von Herberstein, in the 16th century Russians called the [Ural Mountain] range by a variety of names derived from the Russian words for rock (stone) and belt. The modern Russian name for the Urals (Урал, Ural), first appearing in the 16th–17th century when the Russian expansion into Siberia was in its heroic phase, was initially applied to its southern parts and gained currency as the name of the entire range during the 18th century. From the 13th century, in Bashkortostan there has been a legend about a hero named Ural. He sacrificed his life for the sake of his people and they poured a stone pile over his grave, which later turned into the Ural Mountains.>>

Too soon to know if any pieces of the " Ural rock " been picked up yet ?

There appear to be credible reports that at least a few small pieces have been recovered. The appear stony, probably chondritic.

Chebarkul Lake meteorites confirmed as fragments of Russian fireball
Astrobob, February 17, 2013

[b][color=#0000FF]Stony chondrite meteorites were found around this hole in Lake Chebarkul. Credit: Andrey Orlov[/color][/b]

---

<<The Russian International News Agency (RIA Novosti) confirms that the small half-inch black rocks littered around the hole on frozen Lake Chebarkul near Chelyabinsk have been confirmed as meteorites from Friday’s exploding fireball.

Victor Grokhovsky of Urals Federal University and a member of the Russian Academy of Sciences’ Committee on Meteorites, described the fragments as “chondrites”, a common type of stony meteorite knocked from the crust of an asteroid. The space rocks have an iron content of about 10 percent. Gokhovsky hopes the new fall will be named Chebarkul, after the nearest town. Most meteorite falls are named after the nearest city, post office or important landmark after being reviewed by the Nomenclature committee of the Meteoritical Society, a group of over 1000 scientists and meteorite enthusiasts from around the world.

Carbonaceous chondrites are fragile, carbon-rich meteorites that easily shatter into dust and small bits during a fall. If that’s what we’re dealing with here, meteorite hunters better get cracking – this type erodes quickly. Divers found no trace of any meteorites in the lake at the bottom of the hole today.

It is odd though that two days have gone by without a single significant fragment found. Meteorites, which develop a black fusion crust on atmospheric entry, would show up beautifully against the snowy Russian landscape. So what gives? How long will see purported Chelyabinsk “meteorites” pop up on eBay before the real item finally shows? Only hours after the fall, the first dubious specimens appeared on the auction site. Not a one of them looks like a fresh fall and some are clearly not meteorites. Buyer beware!>>

[alter-ego]

This one came in at a low angle very fast. If it had made a more direct shot at us, it would have been much worse correct?

Are you talking about the Russian meteor? It came in shallow, but very slow (~18 km/s, near the low end of the possible range). It was the low speed and shallow angle that allowed it to survive so far down into the atmosphere. Had it come directly down, it probably would have exploded much higher and no shock wave would have reached the ground at all.

I agree the meteor would have exploded higher but, from what I've read, it isn't clear that the grazing incidence case would have been worse.

The details of how much energy reaches the ground is complicated by power dissipation along the air column before disruption. It seems that for normal incidence, the explosive energy would be larger because less energy is absorbed by the atmosphere (slowing the meteor down) before disruption. Even for a volatile rich meteor, size matters, i.e. there is a size above which the energy reaching the ground increases even for higher altitude explosions (within some size range, maybe disruption altitudes also level off?). So for the Russian meteor, the trade off between a reduced shockwave at the ground due to greater altitude, and greater disruption energy because of higher kinetic energy, is not clear. Ultimately energy is conserved for either grazing or normal incidence cases. I'm only bringing into the discussion the interplay between disruption energy and absorbing volumes of atmosphere.

Other than conlcuding the explosion would occur at a higher altitude, it isn't clear to me what the magnitude of the shockwave reaching the ground would be.

[Steve Dutch]

The California meteor is a run of the mill bolide, maybe the size of a marble, that you can see every week or so from any place on earth if you wait long enough.

One site is making a big to do about the yield of the Russian meteor being raised from 300 to 500 kt. When it comes to the calories in a jelly donut, you can burn it in a bomb calorimeter, measure the temperature rise of the surrounding water, and determine the energy. You can use an electric heater to heat water, measure the temperature rise, and relate electrical and chemical energy scales. It's a little hard to enclose a nuke in a calorimeter. We do know the blast effects of large chemical explosions, and we know the energy released in the chemical reactions, and the blast effects follow scaling laws. Typically the energy is proportional to the volume of the effect, or the cube root of the radius. The smallest nukes overlap the largest chemical explosions, but we've never set off tens of thousands of tons of explosive at once. We estimate the yield of very large nukes from blast effects, scaling up from smaller explosions. But blast effects depend on the setting. Who wants us to set off lots of nukes at 20 km to calibrate the Russian event? Thought so.

Bottom line is the difference between an estimate of 300 kT and 500 kT is not worth discussing. Even less do we know the exact energy of the Chesapeake Bay or Sudbury impacts. Order of magnitude is about it.

[cmflyer]

Two questions:
1. Is today's APOD video in real time?
2. Was the shockwave experienced in Russia a result of the object ramming through air hypersonically, or from it exploding, or both?

Thanks All, great discussions!

[neufer]

1. Is today's APOD video in real time?

As it indicates, it is 106 minutes in 19 seconds (or about 335 times normal speed).

2. Was the shockwave experienced in Russia a result of the object ramming through air hypersonically, or from it exploding, or both?

The shockwave was the result of numerous objects ramming through air hypersonically after the meteor rapidly disintegrated into many fragments. It is really the only efficient means for the initial kinetic energy of a stony asteroid to be transformed into "airburst" energy.

Code: Select all

Airburst estimates for a stony asteroid with a diameter ranging from 30 to 85 meters

Diameter 	Kinetic energy 	Airburst energy    Airburst altitude 	Average frequency
------------------------------------------------------------------------------------------------------------
30 m  	  	   708 kt	   		 530 kt  		    16.1 km  		    185 years
50 m  	  	   3.3 Mt 		 	  2.9 Mt 		      8.5 km 	   	  764 years
85 m         	16.1 Mt 		  	15.6 Mt 		     0.435 km	  	  3300 years

[Chris Peterson]

The details of how much energy reaches the ground is complicated by power dissipation along the air column before disruption...

This applies to much more massive bodies than the one over Russia. For such a small body as that, the dynamics are much simpler. Had it been just a bit faster, or just a bit steeper, it's likely that there would have been no significant shock wave at the ground.

[Chris Peterson]

2. Was the shockwave experienced in Russia a result of the object ramming through air hypersonically, or from it exploding, or both?

Primarily from the explosion. When the object fragmented, a huge surface area was exposed to ablation, superheating a large volume of air (a cylinder because of the motion of the bodies). This is the primary source of the shockwave. There were secondary shockwaves created by the smaller pieces, but these were much lower energy (you can hear them after the primary shock in some of the videos). At the disruption height of 27 km, most of the energy from the supersonic shock waves dissipated before reaching the ground.

[Chris Peterson]

Bottom line is the difference between an estimate of 300 kT and 500 kT is not worth discussing. Even less do we know the exact energy of the Chesapeake Bay or Sudbury impacts. Order of magnitude is about it.

You are mistaken. The energy can be calculated quite accurately by looking at the signal from microbarometers, of which there is a worldwide array. In addition, the energy can be calculated from the light curve if it was accurately recorded by one of the DOD monitoring satellites (which it almost certainly was, although that information may not be released publicly).

There is a standard conversion between joules and kilotons of TNT. Because the dynamics of the energy release are different between a meteor and a nuclear bomb, it is somewhat inaccurate to compare a 500 kT energy meteor event to a 500 kT nuclear explosion. But the 500 kT value itself is quite accurate- probably to better than 10%- as a measure of the total energy released.

[rstevenson]

... The smallest nukes overlap the largest chemical explosions, but we've never set off tens of thousands of tons of explosive at once. ...

Not deliberately. But the Halifax Explosion of Dec. 6th, 1917 was a pretty big bang. The French ship Mont-Blanc, which was loaded with 2,300 tons of wet and dry picric acid, 200 tons of TNT, 10 tons of gun cotton and 35 tons of benzol, collided with the Norwegian vessel SS Imo in the narrows of Halifax harbour. The blast resulted in about 2000 dead and a further 9000 injured. From Wikipedia...

Until the Trinity test that led to the development of the atomic bomb, it was the largest man-made explosion in recorded history with an equivalent force of roughly 2.9 kilotons of Trinitrotoluene (TNT). In a meeting of the Royal Society of Canada in May 1918, Dalhousie University's Professor Howard L. Bronson estimated the blast at some 2.4 million kilograms of high explosive.

Considering how startlingly powerful the comparitively small blast in Russia a couple of days ago seems in the many videos we have of it, it's quite difficult to comprehend what it must have been like in Halifax and Dartmouth on that terrible day in 1917.

Rob

[mjimih]

... but these were much lower energy (you can hear them after the primary shock in some of the videos). At the disruption height of 27 km, most of the energy from the supersonic shock waves dissipated before reaching the ground.

Wow thank goodness, because from an elevation almost three times the height of Mt Everest, it was still easily capable of busting out glass over a large area. I'd say we really need to become experts at deflecting these "startlingly powerful" pebbles asap. Friday was about as stark a reminder of just how small we are as I can think of. I mean two big rocks on the same day too! Amazing. We need to build machines now that can be readily used on very short notice.
Bill Nye on the need for deflection technology (a ten year plan);
http://www.youtube.com/watch?v=0QhvLTgcEAg

[Chris Peterson]

Wow thank goodness, because from an elevation almost three times the height of Mt Everest, it was still easily capable of busting out glass over a large area. I'd say we really need to become experts at deflecting these "startlingly powerful" pebbles asap. Friday was about as stark a reminder of just how small we are as I can think of. I mean two big rocks on the same day too! Amazing. We need to build machines now that can be readily used on very short notice.
Bill Nye on the need for deflection technology (a ten year plan)

Objects like that over Russia are not a significant threat. They are not uncommon, and usually go largely unnoticed. It was very unusual for such a small body as this to descend so deeply before breaking apart, and bad luck that it did so directly over a population center. In practice, it is very unlikely that we would even concern ourselves with objects in this size range, as doing so would consume vast resources with virtually no gain. Even DA14 would be unlikely to cause much damage if it hit the Earth.

Developing detection and deflection technology makes good sense, but probably only for objects larger than about 100 meters.

[neufer]

Developing detection and deflection technology makes good sense, but probably only for objects larger than about 100 meters.

Detection technologies for objects less than about 100 meters make good sense:

• 1) To provide better statistics on how often such events occur.
  2) To give folks in populated land regions a heads up.
  3) To assist fresh meteorite searchers in unpopulated land regions.

<<2008 TC3 (Catalina Sky Survey temporary designation 8TA9D69) was a meteoroid 2 to 5 meters in diameter and weighing 80 tonnes, that entered Earth's atmosphere on October 7, 2008, at 02:46 UTC (05:46 local time). The meteoroid was notable as the first such body to be observed and tracked prior to reaching Earth. It exploded an estimated 37 kilometers above the Nubian Desert in Sudan. A search of the impact zone that began on December 2008 turned up 10.5 kilograms of meteorites in 600 fragments, which are surviving pieces of the meteoroid. The meteorites are of a rare type known as ureilites [Not to be confused with Uralites], which contain, among other minerals, nanodiamonds.>>

[Chris Peterson]

Detection technologies for objects less than about 100 meters make good sense:

Agreed, however for the most part this is achieved by monitoring meteors, not searching for meteoroids. Very few resources are dedicated to detecting such bodies while they are in space, because the value of such data is quite limited.

[cmflyer]

2. Was the shockwave experienced in Russia a result of the object ramming through air hypersonically, or from it exploding, or both?

Primarily from the explosion. When the object fragmented, a huge surface area was exposed to ablation, superheating a large volume of air (a cylinder because of the motion of the bodies). This is the primary source of the shockwave. There were secondary shockwaves created by the smaller pieces, but these were much lower energy (you can hear them after the primary shock in some of the videos). At the disruption height of 27 km, most of the energy from the supersonic shock waves dissipated before reaching the ground.

Getting both answers (see Art's answer above yours). The boom sounds like a classic double sonic-boom, and I agree with Art that the fragments seem to be making their own smaller sonic-booms. Perhaps the brightest flash corresponds with max-Q, which, assuming the velocity was down into the Mach 1 or 2 range by that time, would cause the main boom, create maximum heat, and shatter the object.

[Chris Peterson]

Getting both answers (see Art's answer above yours). The boom sounds like a classic double sonic-boom, and I agree with Art that the fragments seem to be making their own smaller sonic-booms. Perhaps the brightest flash corresponds with max-Q, which, assuming the velocity was down into the Mach 1 or 2 range by that time, would cause the main boom, create maximum heat, and shatter the object.

The parent body was still hypersonic when it exploded, or it would not be luminous. Ablation generally stops at about Mach 5. This body was still well above that.

[ta152h0]

I remember the 1972 meteor that famously, and lucky for us was photographed by an amateur , streaked ove a lake. I don't remember reading about a shock wave in Scientific American at the time. Maybe it was going too slow. I do remember reading it came back for a final visit.

[Chris Peterson]

I remember the 1972 meteor that famously, and lucky for us was photographed by an amateur , streaked ove a lake. I don't remember reading about a shock wave in Scientific American at the time. Maybe it was going too slow. I do remember reading it came back for a final visit.

That was the Grand Teton meteor. It was an Earth grazer, meaning it only dipped into the upper atmosphere. It was far too high for any audible acoustic energy to reach the ground. In all likelihood it was smaller and less massive than the body that exploded over Russia. Based on its orbital elements (as modified by its 1972 encounter with the Earth) it should have returned quite close to the Earth in 1997, but it was not detected.

[neufer]

I remember the 1972 meteor that famously, and lucky for us was photographed by an amateur , streaked ove a lake. I don't remember reading about a shock wave in Scientific American at the time. Maybe it was going too slow. I do remember reading it came back for a final visit.

That was the Grand Teton meteor. It was an Earth grazer, meaning it only dipped into the upper atmosphere. It was far too high for any audible acoustic energy to reach the ground. In all likelihood it was smaller and less massive than the body that exploded over Russia. Based on its orbital elements (as modified by its 1972 encounter with the Earth) it should have returned quite close to the Earth in 1997, but it was not detected.

<<The 1972 Great Daylight Fireball (or US19720810) was an Earth-grazing meteoroid that passed within 57 kilometres of the surface of the Earth at 20:29 UTC on August 10, 1972. It entered the Earth's atmosphere at 15 kilometres per second in daylight over Utah, United States (14:30 local time) and passed northwards leaving the atmosphere over Alberta, Canada. It was seen by many people and recorded on film and by space-borne sensors. Analysis of its appearance and trajectory showed it was a meteoroid about 3 metres in diameter, if a carbonaceous chondrite, to 14 metres, if made of cometary ices. It was in the Apollo asteroid class in an Earth-crossing orbit that would make a subsequent close approach to Earth in August 1997. In 1994, Czech astronomer Zdenek Ceplecha re-analysed the data and suggested the passage would have reduced the meteoroid's mass to about a third or half of its original mass. The meteoroid's 100-second passage through the atmosphere reduced its velocity by about 800 metres per second and the whole encounter significantly changed its orbital inclination from 15 degrees to 8 degrees. If it had not entered at such a grazing angle, this meteoroid would have lost all its velocity in the upper atmosphere, possibly ending in an airburst, and any remnant would have struck Earth at terminal velocity.>>

<<The 1972 Great Daylight Fireball (or US19720810) meteoroid is described in the preface of the first chapter of Arthur C. Clarke's The Hammer of God.

The Hammer of God is a science fiction novel by Arthur C. Clarke originally published in 1993. A good portion of the book details the life of spaceship-captain Robert Singh (including his running a marathon race on the Lunar surface and uprooting his life and moving to Mars). When it is discovered that the asteroid Kali is likely to hit Earth, Singh's ship Goliath makes an emergency voyage to Kali with a load of thrusters to set up on the asteroid, hopefully nudging the rock's orbit just enough to push it clear of Earth. In the meantime, a religious sect called Chrislam, originally founded by a female veteran of the Persian Gulf War, believes that they can convert a human being into a few terabytes of computer information, and then transmit this data across space to Sirius (where they believe aliens reside); members of the sect also come to believe that the asteroid is meant to destroy the Earth. They [Geckzilla, Owlice, Moonlady, Ann and Margarita] thus sneak a bomb on board the Goliath and ruin the thrusters. While Singh uses the Goliath itself as a thruster to move the asteroid, the world government on Earth rushes to reconstruct one of the planet's long-decommissioned nuclear weapons, hoping to break the peanut-shaped Kali in two.

While filmmaker Steven Spielberg optioned the rights to The Hammer of God for film production, the resultant movie, Deep Impact (1998), was dissimilar enough to the book that Clarke received no on-screen credit for the movie.>>

Arthur C. (The Glamor of Hog) Neuendorffer

[fercapa]

Hello. This was my observation. I lost the asteroid in some moments because I was showing it in a public observation and left the camera alone...

Watch it better at HD and fullscreen. And even better downloading original file from http://vimeo.com/59956839

[neufer]

Why don't we have any photos of asteroid 2012 DA14 if it came so close?

[Steve Randall]

Does the asteroid seem to be spinning? Maybe 2 or 3 revs/second? Did anyone do an FFT on luminosity or something?

[neufer]

Click to play embedded YouTube video.

Does the asteroid seem to be spinning?
Maybe 2 or 3 revs/second?

2012 DA14 is not only spinning...it is tumbling wildly.

http://www2.eng.cam.ac.uk/~hemh/rigid_body.htm

However, remember that you are observing time lapse
sped up ~300 times so definitely not at "2 or 3 revs/second."

[Chris Peterson]

Does the asteroid seem to be spinning? Maybe 2 or 3 revs/second? Did anyone do an FFT on luminosity or something?

All asteroids are spinning, and most are spinning on more than one axis (tumbling).

[ta152h0]

There was a mention of a camera shake by one observer of the asteroid fly by. Is it possible to measure the distance of a background star by measuring the amplitude of the shake of a nearby object and compare the amplitute of the shake on a far away object and just bdo the math ? Couldn't be that simple , could it ?