The meteor that streaked over Russia Friday and exploded about 10 miles above the surface, creating a powerful pressure wave that injured hundreds of people, was a rare phenomenon, but it was not related to another unusual astronomical event that occurred at about the same time—the much-publicized asteroid that was scheduled to make a close pass of Earth Friday afternoon.
MIT planetary scientist Richard Binzel said that the meteoroid that came down over Russia was roughly the size of a van or small truck, and it is just a coincidence that it occurred around the same time as a close call with the asteroid 2012 DA14. That asteroid, about half the size of a football field in diameter, had long been predicted to come within 17,200 miles of Earth—a historic close approach for an object of that size.
“We’re looking at it carefully. It turns out they almost certainly are not related, which is amazing because of the coincidence,” Binzel said. The object that hit Russia, Binzel said, was travelling north to south, whereas the asteroid 2012 DA14 is moving south to north.
That means the two space rocks were more than a million miles apart.
Timothy Spahr, director of the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics, agreed. Because the object came from the wrong direction of the sky to be DA14, he said, scientists know it is not a fragment of the large asteroid.
Meteoroids—space dust or rocks flying through the solar system—routinely strike the Earth’s atmosphere and become meteors, Binzel said, although events the size of the one in Russia are uncommon.
Every day, 100 tons of space dust bombards the atmosphere, Binzel said. That burns up before reaching the ground.
Larger collisions, the size of the event in Russia, happen only once every few decades. But because so much of the Earth is ocean, only about once a century does something comparable occur over an inhabited area.
“Objects falling over the oceans could be almost completely missed,” Spahr said in an e-mail. “Only the Air Force and Department of Defense have information on a lot of the airbursts that are unobserved from the ground.”
This is the largest recorded meteor, Binzel said, since the 1908 Tunguska event, when a larger object exploded over Siberia.
The atmosphere largely protected the Earth, Binzel said, heating up the meteor and causing it to break apart. Scientists believe the meteor hit the atmosphere at more than 40,000 miles per hour, but exploded about 10 miles above the Earth. What reached the ground were fragments of rock, known as meteorites—and a pressure wave and sonic boom that caused destruction on the ground. Binzel said if the original space rock—the meteoroid—had been slightly smaller, it likely would have exploded further from the Earth’s surface and the pressure wave would not have made it to the ground.
Binzel said scientists in Russia are already making efforts to collect meteorites that hit the ground. He hopes to examine some of those specimens himself.
“These typically would break into fragments, hand-sized or smaller, and there could be hundreds or thousands of them,” Binzel said. “We hope there are, because scientifically we would hope to pick them up and bring them into laboratories.”
Scientists closely monitor near-Earth asteroids that could pose a risk to the planet, but Binzel said that something the size of the Russian meteoroid was small enough that it could easily be missed. Those objects are detected by telescopes, logged in databases, and their future orbits are carefully predicted.
“We could get lucky and see something of the size that came over Russia, but surveys are more dedicated to objects that have to do with more extensive damage,” Binzel said.Carolyn Y. Johnson can be reached at firstname.lastname@example.org. Follow her on Twitter @carolynyjohnson.