This satellite image taken Thursday shows the oil slick in the Gulf of Mexico as it nears the shoreline, threatening wildlife along Louisiana's fragile islands and barrier marshes. NASA/AP hide caption

itoggle caption NASA/AP

Stephen Quake (left) and Euan Ashley review genetic risk factors that Ashley and colleagues found in Quake's genome. Norbert von der Groeben/Stanford School of Medicine hide caption

itoggle caption Norbert von der Groeben/Stanford School of Medicine

Red and green aphids get their different colors by producing carotenoids, or color compounds. Courtesy of Charles Hedgcock, R.B.P. hide caption

itoggle caption Courtesy of Charles Hedgcock, R.B.P.

This illustration shows the asteroid 24 Themis flanked by two small fragments that broke off following a crash more than 1 billion years ago. The bottom fragment's cometlike tail comes from the sublimation of ice from its surface. Gabriel Perez, Servicio MultiMedia, Instituto de Astrofisica de Canarias, Tenerife, Spain hide caption

itoggle caption Gabriel Perez, Servicio MultiMedia, Instituto de Astrofisica de Canarias, Tenerife, Spain

Two ships float near the massive oil slick spreading in the Gulf of Mexico after a drilling rig sank last week off the coast of Louisiana. The slick is 80 miles long and 40 miles wide and growing. Brendan Farrington/AP hide caption

itoggle caption Brendan Farrington/AP