A selfie on mars.

• Position: THE BIG PICTURE - Photograph

Say cheese! This selfie was recently taken by NASA rover Curiosity in one of Mars's craters. (The photo is actually a composite of dozens of images; that's why you can't see the rover's outstretched robotic arm that snapped the selfie.) Curiosity has been roaming Mars since 2012, studying its rocks and atmosphere. So far, the 1,982-pound rover, which is powered by plutonium and is expected to fully function for another six to seven years, has already made some vital discoveries. For one, it's learned that Mars once had plenty of water...