It’s rare, but sometimes I wish I spoke Norwegian.
Last week, it was reported that a large meteor exploded over Norway. This is interesting news to say the least, as the explosion was reported as being pretty big. Pictures of the streak in the sky were published, reports were made of seismic disturbances, etc. We get lots of reports like this, and only rarely are they legit.
This one still looks legit, but now there is some confusion. The initial report said that the explosion was Hiroshima-sized (something like 13 thousand tons of TNT), but now another astronomer from Norway is saying that was exaggerated. In the new press release, this other astronomer, Professor Kaare Aksnes, is saying the explosion was smaller than that. I think. I’m not precisely sure what he’s apologizing for, to be honest. The article summarizes what he said, but his original statement is in Norwegian! So I can’t really tell what’s what. I don’t trust translation software, so if there are any Norwegian BABloggers out there, feel free to translate what he said and post it in the comments!
June 15th, 2006 at 11:50 am
Well, not norweigan, but I can read it a little. He appears to be saying that that stone might have had that energy before it entred the atmosphere, but lost most of on the way down. He says, (maybe speculating a bit) that the impact is comparable to a a powerful conventional bomb.
June 15th, 2006 at 11:53 am
BTW, he also says that the hiroshima bomb corresponds to 40 000 ton TNT, is this a metric vs. imperial thing?
June 15th, 2006 at 12:05 pm
Hi
I’m from Denmark, and danish and norwegian are very much alike, so I think I can clarify a bit.
Professor Kaare Aksnes works at the Institute for Theoretical Astrophysics at the University of Oslo.
Kaare Aksnes isn’t apologizing in his norwegian commentary. He is simply sorry that the power of the impact has been overestimated to be like a Hiroshima-bomb and that the estimate seemed to come from his institute.
Kaare Aksnes actually says the energy has been “very strongly overdone” (norwegian: “… meget sterkt overdrevet”).
The first part of the english article is pretty well the essens of the norwegian article. The second part of the english article (after the lines where he compares the impact to a conventional bomb) has nothing to do with the norwegian article by Kaare Aksnes, but is (I think) from the original (and overestimating) reports.
Best Regards
Leif B. Nielsen
June 15th, 2006 at 12:10 pm
Ah, I see. Thanks!
Various numbers pop up all the time for the yield of the Hiroshima bomb, but a kiloton is a standard unit meaning 1000 tons of TNT (4×1019 ergs = 4×1012 Joules).
June 15th, 2006 at 12:29 pm
He doesn’t apologize, he expresses regret that the power of the explosion have been exaggerated or overestimated.
June 15th, 2006 at 3:56 pm
This is a complete translation of the Norwegian article (but please keep in mind, I am not a native speaker, so some words may be wrong, but the context has been preserved to the best of my abilities)
Over-estimated explosive force of meteorite impact
Statements regarding that the recent meteorite-impact in Nord-Troms had the same explosive force as a Hiroshima bomb are rejected in this commentary by astronomy professor Kaare Aksnes, from the Institute for theoretic astrophysics at the University of Oslo.
It is unfortunate that it has been claimed that the meteorite-impact in Nord-Troms could have had an explosive force comparable to a Hiroshima bomb. This is a large exaggeration.
It is also unfortunate that it can be perceived as if our institute is behind this statement.
The Hiroshima bomb had an explosive force which is equivalent with approximate 4*10e7 kilos of TNT. This corresponds to the kinetic energy of a rock 3 m in radius, with a density of 3,5 g/cm3 and a velocity of 30 km/s as it enters the Earths upper atmosphere.
Such impacts occur several times every year and are registered by satellites which monitor the atmospheric nuclear testing ban.
The point of the matter is that this rock is almost completely combusted [vaporised] by the heat of friction, and what ever survives down to the ground will hit with a velocity probably smaller than a bullet.
Almost all of the original energy is dissipated, partly as light and sound during the seconds of the impact in Reisa valley in Nord-Troms. I believe that the impact energy was equivalent to a large conventional bomb.
The latest documented impact with an energy comparable to the Hiroshima bomb occurred in Tunguska in the Siberian in 1908. It has been calculated that it could have been an object with approximately 50 m radius which exploded several kilometres over Tunguska and flattened the forest in an area with 25 km radius.
I can also inform that the Astrophysical Institute participates in a observation programme with Nordic Optical Telescope in Las Palmas, the Canaries to survey the risk of impact with close-earth asteroids.
As of present there has been no discovery of any object which presents any danger for the foreseeable future.
June 16th, 2006 at 1:50 pm
The Bad Astronomer said:
“Various numbers pop up all the time for the yield of the Hiroshima bomb, but a kiloton is a standard unit meaning 1000 tons of TNT (4×1019 ergs = 4×1012 Joules).”
OK, BA, erm …. how many ergs or joules in a ton of TNT? I tried to do a web search on the Gibbs energy of the reaction of TNT (from which, along with the molecular weight of trinitrotoluene that I can calculate, would give me the liberated energy per unit weight), but I couldn’t find a page that actually associated Gibbs energy with the oxidation of TNT (well, not insofar as providing numbers).
Strange, that.
June 17th, 2006 at 10:22 am
spaceweather.com sez,
FIREBALL UPDATE: 300 tons of TNT. That’s the kinetic energy of the meteoritic fireball sighted June 7th in Norway, according to Prof. Peter Brown of the University of Western Ontario. Brown’s doctoral student, Wayne Edwards, arrived at this figure by analyzing infrasound and seismic data. Early reports of a Hiroshima-like event (12,000+ tons of TNT) were exaggerated.
“An object like this hits Earth about once a month,” notes Bill Cooke of the Marshall Space Flight Center. For comparison, “the Norwegian event was similar to, but somewhat less energetic than the Park Forest meteorite impact of 2003.”
June 19th, 2006 at 5:01 pm
A fellow member at The Straight Dope responded with this translation. I hope it helps.
“Recent claims that the meteor impact in Northern Troms may have had an explosive force comparable to the Hiroshima atomic bomb are vehemently rejected in this comment by Kaare Aksnes, professor of astronomy at the Institute of Theoretical Astrophysics, University of Oslo.
It is regrettable that claims have been made suggesting that the meteor impact in Northern Troms may have had an explosive force comparable to the Hiroshima atomic bomb. These claims are extremely exaggerated.
It is likewise regrettable that it may appear as if our Institute is behind these claims.
The atomic bomb detonated over Hiroshima had an explosive force determined as being equal to about 40,000 tons of TNT. This is approximately equal to the kinetic energy of a rock with a radius of 3 meters, a density of 3.5 grams per cubic cm, and a velocity of 30 km/s, as it enters the upper parts of the Earth’s atmosphere.
Several such impacts occur each year, and are observed by satellites set up to monitor the ban on atmospheric nuclear detonations.
However, such a rock would be almost entirely incinerated in the atmosphere due to heat caused by friction, and any remains that might make it to the ground would impact with a velocity comparable to that of a bullet shot from a rifle.
Almost all of the original energy would have been lost on the way to the ground, partly as a bright flash of light and thunderous noise in the seconds before the impact in the Reis Valley in Northern Troms. My estimate would be that the power of the impact would at most have been that of a somewhat powerful conventional bomb.
The last documented impact with an energy comparable to the Hiroshima bomb occurred in Tunguska, Siberia, in 1908. Calculations have shown that this may have been due to an object with a radius of 50 meters, exploding several kilometers above Tunguska, flattening trees in an area with a radius of 25 km.
I can also inform the public that the Institute of Astrophysics is taking part in a program involving the Nordic Optical Telescope at La Palma, Canary Islands, intended to assess the danger of collisions with near-earth asteroids.
So far, no objects have been discovered that will pose a threat in the foreseeable future.”
June 20th, 2006 at 4:36 pm
You were just lately wondering why we don’t hear more about metre-size lumps of space stuff going pop in the upper atmosphere, and whether anyone keeps track of it. I guess we know now. He do. And they probably keep it quiet (so to speak) on grounds of (inter)national security.