The Chelyabinsk Lesson: Beware Small Asteroids


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Main mass of the Chelyabinsk fall at the Chelyabinsk State Museum of Local History shortly after recovery from Chebarkul Lake. Credit: Science/AAAS

Ever since February, when a fireball appeared over the sky in central Russia and created shock waves that shattered windows before the meteor plummeted into the ground, scientists have analyzing the Chelyabinsk incident to try to determine where it came from and why they couldn't see this damaging space rock coming. Today, studies backed by a litany of scientists and appearing in both of the biggest journals, Nature and Science, document everything they've discovered.

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The wealth of data includes best guesses about how old Chelyabinsk is (4.45 billion years, just a shade younger than the solar system itself), where the heck it came from (it was probably once part of a bigger asteroid that orbits near Venus), and why it broke up in our atmosphere into many smaller pieces. But the most telling takeaway is about Chelyabinsk's cousins.

Impact site of the main mass of the Chelyabinsk meteorite in the ice of Lake Chebarkul. Credit: Eduard Kalinin]

In reconstructing the asteroid from its fragments and recorded evidence of its descent to Earth, scientists estimated that Chelyabinsk was around 62 feet, or 19 meters, in width. Yet even at this (relatively) small size, the space rock caused an airburst equal to about 500 kilotons of TNT. (The largest such airburst of the modern era was the 1908 Tunguska asteroid, which exploded over Russia with the equivalent of 5 to 15 megatons.) Scientists have recorded about 1000 objects the size of Chelyabinsk in the area around the Earth, the Wall Street Journal says. However, a meteor expert tells them, there might be a million of them. And according to, the a historical analysis of impacts suggests Chelyabinsk isn't exactly a fluke: Asteroids of this size might hit the Earth more often than astronomers had previously thought.

It's easy to get worked up about the extinction-level event asteroids—Armageddon-sized space rocks large enough to wipe out humanity or wreak planet-wide devastation. Chelyabinsk-sized asteroids can't do that. But they certainly pack enough punch to devastate a major city if they happened to land in just the wrong spot. NASA is trying to step up its near Earth object-spotting game, but even so, many of these smaller asteroids are too small to be seen (and Chelyabinsk itself came toward Earth from the direction of the sun, so it's glare would have rendered it invisible). Instead, astronomers say, the focus should be on finding these asteroids when they are approaching Earth and easier to see—but still far enough away to allow for evacuations or other emergency responses.

Chelyabinsk meteorite (diameter ~4 cm) showing shock veins. Credit: Science/AAAS

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