An artist's depiction of NASA's Spirit rover on the surface of Mars. Spirit became unresponsive in March 2010. NASA announced it had ended attempts to communicate with the rover on May 24, 2011. NASA hide caption

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XMRV, a mouse virus, may be an artifact of laboratory experiments rather than the cause of chronic fatigue syndrome. Whittemore Peterson Institute hide caption

itoggle caption Whittemore Peterson Institute

Framed in the doors of the Kennedy Center's Vehicle Assembly Building, the crawler begins the long journey toward Launch Pad 37B with space shuttle Discovery in April 2005. This enormous cross between a tank and a cargo ship is the largest self-powered land vehicle in the world. NASA hide caption

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A student works on her robot gladiator. Courtesy of National Tooling and Machining Association hide caption

itoggle caption Courtesy of National Tooling and Machining Association

A study published in the journal Science last December suggested that a bacterium found in California's Mono Lake was able to substitute arsenic for phosphorous. But that conclusion has many critics. Miss Bliss 55 via Flickr hide caption

itoggle caption Miss Bliss 55 via Flickr

A satellite image shows a field of what may be buried pyramid sites in Egypt. Courtesy of DigitalGlobe Images hide caption

itoggle caption Courtesy of DigitalGlobe Images