What we know about the Russian meteor event on Feb 15, 2013

Heidi Hammel
The Planetary Society
Sun, 17 Feb 2013 10:00 UTC

We have the technology to provide warning about these potential disasters

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 = ~10¹⁵ 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.

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.

Comment: The problem isn't a lack of technology; the problem is that our leaders have chosen to ignore the problem.

From Letters From The Edge:

Awareness of the possibility of large impact events on Earth, although long present among a handful of the most imaginative thinkers, has come of age in this century as a result of studies of Arizona's Meteor Crater and the Tunguska fireball of June 30, 1908, in Siberia, spacecraft observations of cratering on Earth and other rocky bodies, and astronomical surveys of the near-Earth asteroid and comet populations. Appreciation of the effects of large impacts has developed in response to these studies and to the unclassified literature on the effects of large nuclear weapons. [...]

The most intensively studied impact phenomenon, impact cratering, is of limited importance, due to the rarity and large mean time between events for crater-forming impacts. Almost all events causing property damage and lethality are due to bodies less than 100 meters in diameter, almost all of which, except for the very largest and strongest, are fated to explode in the atmosphere. ... Since explosions greater than 1 gigaton TNT are rare on this short of a time scale, we are forced to conclude that the complex behavior of smaller bodies is closely relevant to the threat actually experienced by contemporary civilization. [...]

The large majority of lethal events (not of the number of fatalities) are caused by bodies that are so small, so faint, and so numerous that the cost of the effort required to find, track, predict, and intercept them exceeds the cost of the damage incurred by ignoring them.

(John S. Lewis, Professor of Planetary Sciences at the Lunar and Planetary Laboratory, Co-director of the NASA/University of Arizona Space Engineering Research Center, and Commissioner of the Arizona State Space Commission in: Comet and Asteroid Impact Hazards on a Populated Earth, 2000; Academic Press)