Months after a 62-foot-wide fireball streaked through the morning sky over Chelyabinsk, Russia, scientists are starting to get a handle on the rock's composition, trajectory and impact. Three papers released this week, two in Nature today and one forthcoming in Science tomorrow, reconstruct the event, finding that the superbolide (a bright fireball) was even larger than we previously thought, and that the risk of meteorites of this size hitting the earth may be underestimated.
The papers confirm that the meteorite was an ordinary chondrite, the same stony rock that Japan's Hayabusa spacecraft recovered from the asteroid Itokawa in 2010. It likely originated from the Flora asteroid family in the main asteroid belt between Mars and Jupiter. (For a refresher on the differences between meteors, meteorites and asteroids, see here).
In the Science paper, a group of researchers visited villages around the meteorite's landing spot and re-traced its trajectory using the dash-cams and security footage that caught it on tape that morning, at sunrise on Feb. 15, 2013. "Directly below the fireball’s path, the shock wave was strong enough to blow people off their feet," they write.
Some interesting numbers:
- The meteoroid likely started out being about 19 meters in diameter, around 62 feet, and had a mass of 12,000 to 13,000 tons. It entered the atmosphere at a speed of more than 40,000 miles per hour.
- The first shock wave formed at 55 miles above the surface.
- 19 miles above the surface, the meteor peaked in heat and brightness, shining brighter than the sun for people up to 62 miles away. The explosion was equal to about 500,000-600,000 tons of TNT.
- An impact from as long as 4.4 billion years ago created shock veins in the asteroid, making it easier for the rock to break apart.
- 9,000 to 13,000 pounds of meteorite fell to the ground, including the 1,400 pound fragment found in Lake Chebarkul. More than 75 percent of the rock evaporated.
- That biggest fragment created a 23-foot-wide hole in the ice covering Lake Chebarkul, which was more than 2 feet thick at the time.
Most of the damage from the rock came from the air blast, not from actual fragments of meteorite hitting the Earth. As one of the Nature papers points out, it seems our models of air blast damage, based on the effects of nuclear blasts of the same energy, might have been overestimated what actually occurred, since asteroids break up as they fall. In not-so-good news, the researchers estimate the risk of asteroids of this size hitting the Earth might be 10 times greater than previously thought.