THREAT: An asteroid several miles across hits the Earth, pushing most of life into extinction.
REALITY: Clever sleuthing led scientists 30 years ago to find in the Gulf of Mexico and Caribbean the mineral fingerprints of an asteroid several miles across. It was "one of the most devastating events in the history of life and abruptly ended the age of the dinosaurs," according to a 2010 study in the journal Science.
There's no great fix for a space rock several miles long hurtling into the Earth. More than 8,700 near-Earth objects have been discovered, none a serious concern. NASA in February clarified "a very unlikely scenario" that had been receiving much attention, a 460-foot long asteroid discovered in early 2011 that has a 1-in-625 chance of hitting the Earth in 2040.
Astronomers haven't yet had a good occasion to refine their picture of asteroid 2011 AG5's orbit. That opportunity will come in September 2013, when the asteroid will pass within 91 million miles of Earth. NASA expects at that time to "significantly reduce, or rule out entirely any impact probability for the foreseeable future," the agency said.
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