Researchers at the U.S. Geological Survey National Wildlife Health Center in Madison, Wis., use eggs to see if the Asian strain of the H5N1 bird flu virus has entered the U.S. in this photo from 2006. Andy Manis/AP hide caption

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A health official culls chickens on a poultry farm in a village on the outskirts of Katmandu, Nepal. Chickens suspected of being infected with H5N1 bird flu were found in the area in October. Prakash Mathema/AFP/Getty Images hide caption

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A prefectural officer carries a chicken on a poultry farm on Oct. 15 on the outskirts of Kathmandu, Nepal, where chickens suspected of being infected with bird flu were found. Prakash Mathema /AFP/Getty Images hide caption

itoggle caption Prakash Mathema /AFP/Getty Images

The Mariner 2 probe at an assembly facility in Cape Canaveral, Fla., on Aug. 29, 1962. NASA/JPL/Caltech hide caption

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Cmdr. Eugene Cernan tests the lunar vehicle on the surface of the moon during the Apollo 17 mission. NASA hide caption

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Can You Tell Emotion From Faces Alone? A new study suggests that when people evaluated just facial expressions — without cues from the rest of the body — they couldn't tell if the face was showing a positive or negative emotion. Enlarge this photo to see the answers. Hillel Aviezer/The Hebrew University of Jerusalem hide caption

itoggle caption Hillel Aviezer/The Hebrew University of Jerusalem

William Beal, standing at center, started a long-term study on seed germination in 1879. He buried 20 bottles with seeds in them for later researchers to unearth and plant. Michigan State University hide caption

itoggle caption Michigan State University

Koshi, an elephant, makes sounds that imitate Korean words. Stoeger, et. al./Current Biology hide caption

itoggle caption Stoeger, et. al./Current Biology

An artist's impression shows a planet, right, orbiting the star Alpha Centauri B, center, a member of the triple star system that is the closest to Earth. ESO/L. Calcada/AP hide caption

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When a case of the potentially lethal H5N1 bird flu was found in British poultry in 2007, Dutch farmers were told to keep their poultry away from wild birds by closing off outdoor areas with wire mesh. Ed Oudenaarden/AFP/Getty Images hide caption

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Polar bears in the Beaufort Sea in northern Alaska. Scientist Charles Monnett caused a stir with a 2006 report on polar bears that were drowning, apparently owing to a lack of ice. Steve Amstrup/Fish and Wildlife Service hide caption

itoggle caption Steve Amstrup/Fish and Wildlife Service

NASA says it has found proof that water shaped the rocks on the left, in a photograph taken by the Mars rover Curiosity (left). For comparison, the agency released an image of rocks from Earth (right). NASA hide caption

itoggle caption NASA