October 8, 2013
I WAS EXPECTING AN EARTH-SHATTERING KABOOM: Russian Meteor Explosion Might Mean Earth Gets Hit More Often Than We Think.
The latest analysis of the bollide that burst over Chelyabinsk, Russia in February suggests that the risk from such airbursts — which occur when friction in our atmosphere heats up a meteor — may be greater than previously thought.
Meteorite collisions are often compared in size to nuclear explosions, but because they are speeding toward Earth they have momentum that makes them far more destructive. And to make matters worse, they may occur more often than currently estimated.
On the morning of Feb. 15, a fireball lit up the skies above the town of Chelyabinsk. A 12,000-ton bollide estimated to be roughly 20 meters in diameter came screaming into the atmosphere at more than 42,000 mph. Locals could feel the heat from the blast while dozens of dashboard cameras made recordings of the event, which were disseminated widely on social media.
The best estimates of how much energy was released by the Chelyabinsk explosion come from infrasound measurements taken by an array of sensors all over the world. These instruments detect low-frequency sound waves traveling through the atmosphere. The longer the waves’ period is, the larger the explosion. Infrasound measurements are calibrated from atmospheric nuclear testing done in the 1950s, which is why asteroid explosions are often described in megaton units. The bomb that exploded at Hiroshima had a yield of 16 kilotons while the most powerful nuclear weapon active in U.S. service, the B83 bomb, has a yield of up to 1.2 megatons. The Chelyabinsk blast is estimated to have been between 200 and 800 kilotons, on par with a huge atomic weapon.
But meteors explode in a very different way than a typical nuclear bomb, says physicist Mark Boslough of the Sandia National Laboratories, who studies asteroid impacts and is presenting a talk today about the Chelyabinsk event at the American Astronomical Society’s 2013 Division for Planetary Science meeting in Denver.
“When an asteroid explodes, its momentum is conserved and that explosion continues down toward the Earth,” Boslough said.
For that reason, the people who live in Chelyabinsk explosion are very lucky to be alive, he added. If the bollide had come into the atmosphere at a less steep angle, its blast would have been aimed right at the ground, likely doing much more damage.
That an airburst continues traveling in the same direction as a meteorite was only appreciated starting in the 1990s, particularly after the impact of Shoemaker-Levy 9 on Jupiter.
I’d rather spend more tax dollars on studying stuff like this, and less on free birth control.