Moon caves could provide shelter for astronauts exploring Earth's nearest neighbor, researchers say. A new analysis of data gathered by NASA's twin Gravity Recovery and Interior Laboratory (GRAIL) spacecraft, which mapped the moon's gravitational field in unprecedented detail, turned up a number of new candidates for lava tubes -- cave-like structures that could be large enough to house supplies and astronauts. Space is a harsh environment. Radiation from the sun, galactic cosmic rays and constantly falling micrometeorites all present a threat to human explorers. "A lava tube provides a safe haven from all these hazardous environmental conditions," study team member Rohan Sood, a graduate student at Purdue University in Indiana, told Space.com.