Scientists exploring caves in the bone-dry and mostly barren Atacama Desert in Chile stumbled upon a totally unexpected discovery this week: water. They also found hundreds of thousands of animal bones in a cave, possibly evidence of some prehistoric human activity. The findings are preliminary and have not been analyzed. The expedition is designed to learn how to spot caves on Mars by studying the thermal signatures of caves and non-cave features in hot, dry places here on Earth. Scientists think Martian caves, some of which may already have been spotted from space, could be good places to look for...