See other posts from February 2013
We have the technology to provide warning about these potential disasters
Posted By Heidi Hammel
2013/02/15 02:26 CST
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Note: updated after NASA Press Conference today and at 3:22 pm PST with additional details.
Correction: this post initially contained a typo that listed the mass of the meteor at 8 tons, we meant 8000 tons. Currently, the estimated mass ranges from 7000 to 8000 tons. -ed
What we know (subject to change as more information comes in): At 9:20 a.m. local time in Russia, videos show an impactor coming in from the North. Asteroid 2012 DA14 is approaching Earth from the South. These two events are not related. The body is estimated to have been 15 meters across and weighed roughly 8 tons 8000 tons. The resulting airburst would have the equivalent yield of a 1-10 megaton 500 kiloton explosion. Note that these are very rough and extremely preliminary estimates.
Tim Swindle, director of the Lunar and Planetary Lab, released this from Peter Brown, one of the foremost expert on fireballs. The following is from Peter:
What follows are *initial* information gleaned for multiple instrumental sources recording various aspects of the Feb 15, 2013 airburst over Chelaybinsk, Russia (55.2N, 61.4E)
1. Time: The time of the main flare/airburst was 03:20:26 UT on Feb 15, 2013; the fireball began ablation about 30 secs before this time.
2. Based on the long duration of the event and videos, it is clear this was a very shallow entry (certainly less than 20 degrees, maybe more shallow).
3. It is *not* related to 2012 DA14
4. Energy: This is perhaps the hardest value to pin down so early in this investigation. From multiple sensors using multiple technologies a best initial estimate of the total energy of the event is about 300 kilotons of TNT equivalent = ~10^15 J). This could easily be in error by a factor of two. I am confident, however that it is in excess of 100 kTons, making it the largest recorded event since the 1908 Tunguska explosion.
5. Speed: The fireball entered the atmosphere at 18 km/s
6. Damage: The airblast clearly caused window breakage and light structural damage in downtown Chelaybinsk. The exact overpressure at which window failure occurs tends to be probabilistic and varies by construction design (ANSI S2.20, 1983). Normally some damage begins to occur around 500 Pa of overpressure, widespread window damage is expected to occur up to around ten-20 times this value. As the fireball had a shallow trajectory, the cylindrical blast wave would have propagated directly to the ground and would be expected to be intense. This could be further compounded by any fragmentation, quasi-spherical blasts. My impression is that the key here is that the terminal part of the fireball (probably between 15-20 km altitude) occurred almost directly over Chelaybinsk; this was perhaps the single greatest contributor to the blast damage (short range to the main part of the terminal detonation).
7. Comparators: The Sikhote-Alin fall (Feb 12, 1947) in the former Soviet Union was the equivalent of about 10 kilotons TNT, BUT as an iron impactor much of this energy was deposited at the ground rather than at altitude. The Oct 8, 2009 Indonesia event is the most recent similar event at about 50 kTons, but over the ocean.
8. Size: The pre-impacting asteroid was about 15 meters in diameter and had a mass of ~7000 tonnes.
I fully expect revision of some of the numbers above, particularly the estimate of the yield which could *easily* change by a factor of two upon more complete analysis and will likely change as the day progresses
According to NASA, the fact that it broke up in the atmosphere suggests that it was not an iron-nickel asteroid. We do expect fragments to be discovered on the ground. A much more quantitative estimate will come from analysis of the videos, the damage distribution, and the seismic reports. The timing of the shock wave, and the verbal and video reports, are consistent with verbal reports of the Tunguska event in 1908.
I describe the Tunguska event and show impact statistics. One of these megaton events occurs roughly every 100 years. Tunguska was 1908. I ask the audience to do the math.
In my “cosmic collisions” talk (which I’ve been giving for over a decade now), I describe the Tunguska event and show impact statistics. One of these larger events occurs roughly every 100 years. Tunguska was 1908. I ask the audience to do the math. This event was only a question of when, not if, and could have been anywhere on Earth. NASA has programs to detect potential impactors, but due to funding limitations, these searches have been focusing their efforts only on objects that would cause truly catastrophic events. LSST will likewise focus on larger bodies. Fortunately, this 2013 event was not a catastrophe, just a Really Bad Day in Russia.
We have the technology to avert such a disaster. After Comet Shoemaker-Levy 9 and these wake-up calls of 2012 DA14 and the newest Russian meteor blast, if we humans are done in by a rogue asteroid or comet, we have only ourselves to blame. That said, we probably can’t stop these smaller ones from hitting Earth, since they are much harder to detect ahead of time. We can, however, give folks a few hours warning. A tornado siren does not stop tornadoes, but it gives people a chance to take cover. Had the folks in Russia been given even a few minutes warning, many injuries could have been avoided.
Comments:
Ethan Walker: 02/15/2013 05:26 CST
Ethan Walker: 02/15/2013 05:28 CST
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