Space tourist Dennis Tito celebrates after his landing near the Kazakh town of Arkalyk on May 6, 2001. Alexander Nemenov/AFP/Getty Images hide caption

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Researchers who studied pieces of the meteor collected near Lake Cherbarkul say it was a common chondrite meteor. The largest of the 53 fragments was one centimeter in diameter. Photo provided by the Urals Federal University Press Service. Alexander Khlopotov/AP hide caption

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"All these possibilities are out there. And we live in the one that is hospital to our form of life." — Brian Greene James Duncan Davidson/TED hide caption

itoggle caption James Duncan Davidson/TED

"We should search because it tells us how to collaborate our place in the cosmos." — Jill Tarter TED / James Duncan Davidson hide caption

itoggle caption TED / James Duncan Davidson

Nobel Prize winner Saul Perlmutter explains part of his research in astrophysics. Kimberly White/Getty Images hide caption

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A meteor's vapor trail above the city of Chelyabinsk, Russia, on Friday. Vyacheslav Nikulin /EPA /LANDOV hide caption

itoggle caption Vyacheslav Nikulin /EPA /LANDOV

An illustration of what asteroid 2012 DA 14 may look like as it approaches Earth. NASA/JPL-CalTech/EPA /LANDOV hide caption

itoggle caption NASA/JPL-CalTech/EPA /LANDOV