sábado, 16 de febrero de 2013

Lessons from the Russian Meteor Blast

The enormous meteorite explosion over Russia offers the strongest motivation yet for investigation of near-Earth objects.

For those who follow the asteroid impact threat, the 300- to 500-kiloton meteor blast over Russia on February 15th was just a matter of time. It shone brighter than the Sun, and when the shock wave swept across cities and towns more than a minute later, it blew out countless windows and injured at least 1,100 people, mostly by flying glass; seemany more Russian videos and photos. At least one large meteorite fragment accompanied by small black pieces landed in a lake near Chebarkul, a town in the Chelyabinsk region.

As astronomers are keenly aware, Earth sits in a cosmic shooting gallery. Every day, grains, pebbles, and chunks left over from the formation of the solar system streak into the upper atmosphere. Most vaporize very high, causing no harm and giving us beautiful shooting stars

Meteorite smoke
The fireball left a record-breaking train across ther daytime sky.
Nikita Plekhanov
But occasionally, perhaps every few decades to few centuries, our planet gets smacked by an object big enough to cause substantial damage. That's what happened February 15, 2013, at 9:20 a.m. local time in the Ural Mountains of west-central Russia (3:20 Universal Time). More news reports.

According to analysis by meteor expert Peter Brown (University of Western Ontario), the incoming meteoroid carried about 300 kilotons of kinetic energy (about 20 Hiroshimas), entered Earth’s atmosphere at 20 kilometers per second (typical for near-Earth asteroids), was about 15 meters (50 feet) across, and weighed about 7,000 tons. It entered the atmosphere at a grazing angle of less than 20° and burst at a height of 15 or 20 kilometers (10 or 12 miles). An early track-back analysis has put the outer end of its former orbit in the asteroid belt.

(UPDATE: Later in the day NASA released its own estimates: a 10,000-ton object and 500 kilotons of energy.)

This makes it the largest object to hit Earth since the Tunguska event in 1908, beating the Sikhote-Alin meteor in 1947 (also in Russia).

What will probably go in the books as the "Chelyabinsk meteor" fragmented near the city of Chelyabinsk and south of Yekaterinburg. The shock wave shattered glass in at least six cities and towns. Fortunately, we have heard no reports of fatalities, but several dozen people were hurt badly enough to require hospitalization. Obviously, our thoughts and prayers go out to these people, and we wish them a speedy recovery.

Watch another video of the incoming fireball:

By an amazing cosmic coincidence, the impact occurred just 16 hoursbefore the predicted flyby of the larger asteroid 2012 DA14. Because the two objects were moving in completely different directions, there’s no chance the two events are related. 

"This meteor event is in no way related and can't be associated with DA14," says Dan Durda (Southwest Research Institute). "It's complete coincidence." 

But this one-two combo should serve as a wake-up call that we need to take the impact threat seriously. Unlike today’s object that broke up over Russia, 2012 DA14 is large enough that it could cause widespread destruction if it actually hit our planet.

Meteorite video stills
These stills were pulled from an uncredited video at LiveLeak.com, showing the sudden appearance of a fireball out of a clear, blue sky.
With the dramatic video footage, hundreds of injuries, and mass media coverage, I hope and expect that today’s meteor explosion over Russia will serve as a watershed event in public understanding of the impact threat. Astronomers have been warning us for many years that we need to take the impact threat seriously. 

Fortunately, astronomers (mostly in the U.S.) have received sufficient funding and resources that they have identified almost all the kilometer-size near-Earth asteroids that could wipe out civilization, such as the 10-km asteroid that triggered a mass extinction 65 million years ago (extinguishing all dinosaur lineages except birds). None of these large objects will hit our planet in the foreseeable future. 

But smaller bodies remain a concern. As a case in point, on June 30, 1908, an object a few tens of meters across exploded over the Tunguska River region of Siberia — flattening 800 square miles of forest. If that object had exploded over a populated area, it could have killed hundreds of thousands of people.

I often wonder what would have happened if the Tunguska impactor had exploded over the Soviet Union in 1958 or 1968 or 1978 rather than 1908. Given the Cold War hostility and tensions at that time, would the Soviet government have started to lob nukes at the U.S., triggering thermonuclear Armageddon? On the morning of the new meteor, Russian nationalist leader Vladimir Zhirinovsky was immediately on the news deriding the idea that it was a meteor and claiming that it was an American weapons test. And what about meteor explosions over other nuclear-armed nations? The U.S. Air Force has systems that can quickly distinguish a blazingly fast incoming asteroid from a relatively slow ballistic missile, but most nations lack such resources.

Though I deeply regret that people in Russia were hurt by this event, I hope humanity can draw the proper lessons. The “good news” is that it was big enough to serve as a wake-up call, but not big enough to kill people. I don’t stay awake at night worrying about asteroid impacts, and neither should you. Other potential disasters, both natural and man-made, rank far higher on the list of “things you should worry about.” 

But the interesting aspect of the impact threat is that unlike earthquakes, volcanoes, and other natural disasters, we can actually do something about meteor impacts. We can find these objects, we can track their motions, and we can predict their orbits many years into the future. And in the unlikely event that we actually find a dangerous object on a collision course with Earth, we might actually be able to deflect it if given sufficient warning time. Now, every government in the world is keenly aware of the possibility of meteor explosions over its territory.
Posted By Robert Naeye, February 15, 2013