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The destructive space rock was somewhere between 12.4 and 15.5 miles wide. The largest asteroid ever to hit Earth, which slammed into the planet around 2 billion years ago, may have been even more massive than scientists previously thought. Based on the size of the Vredefort crater, the enormous impact scar left by the gargantuan space rock in what is now South Africa, researchers recently estimated that the epic impactor could have been around twice as wide as the asteroid that wiped out the nonavian dinosaurs. The Vredefort crater, which is located around 75 miles (120 kilometers) southwest of Johannesburg,...

From the AGU:Global fires after the asteroid impact probably caused the K-Pg extinctionChicxulub Crater, Yucatán Peninsula, Mexico – Artist’s Impression Image: University of Colorado About 66 million years ago a mountain-sized asteroid hit what is now the Yucatan in Mexico at exactly the time of the Cretaceous-Paleogene (K-Pg) mass extinction. Evidence for the asteroid impact comes from sediments in the K-Pg boundary layer, but the details of the event, including what precisely caused the mass extinction, are still being debated.Some scientists have hypothesized that since the ejecta from the impact would have heated up dramatically as it reentered the Earth’s...

NASA's Jet Propulsion Laboratory, which tracks such flybys, said the asteroid - dubbed 2012 KT42 - was the sixth closest asteroid approach. It was the second asteroid encounter this week. On Monday, another asteroid, measuring 69 feet across, flew by at a distance of 32,000 miles.