An artist's concept shows a NASA Mars exploration rover on the surface of Mars. The twin rovers Spirit and Opportunity were launched in 2003 and arrived at sites on Mars in January 2004. NASA/JPL-Caltech hide caption

Most American cars run on gasoline. But analysts say that's poised to change as electric vehicles take over the market, although they disagree on how soon. Johannes Eisele/AFP/Getty Images hide caption

An American coot flies over Brooklyn's Prospect Park Lake on Feb. 5. Courtesy of August Davidson-Onsgard hide caption

Thanks in part to his original songwriting, singing and guitar-playing, Physics doctoral student Pramodh Senarath Yapa beat out the remaining entrants to win this year's "Dance Your Ph.D." contest. Courtesy of Matthias Le Dall hide caption

A white-tailed deer keeps its ears open while grazing in South Hero, Vt. Rob Swanson/AP hide caption