If scores of cartoons and ancient cave drawings are to be trusted, caves were mankind's first shelter on Earth. How appropriate, then, that NASA thinks caves could play the same role on the moon.
NASA says that the moon has as many as 200 "lunar pits," which aren't exactly craters—they're probably not formed by asteroid or meteor impacts. More likely, they are formed when part of the moon collapses over a void or a cave. Most importantly, many of them probably widen underground, opening up to form large underground caves, where astronauts (or future moon dwellers) could probably live.
"Pits would be useful in a support role for human activity on the lunar surface," Robert Wagner, an Arizona State University researcher who discovered the holes, said in a statement. "A habitat placed in a pit—ideally several dozen meters back under an overhang—would provide a very safe location for astronauts: no radiation, no micrometeorites, possibly very little dust, and no wild day-night temperature swings."
So, that sounds pretty ideal, and would probably be a nice stepping stone before we have full-on lunar colonies on the moon's surface.
The pits were discovered by NASA's Lunar Reconnaissance Orbiter and were detected by an algorithm that Wagner wrote, which automatically scanned the orbiter's high definition images of the moon's surface.
NASA believes the caves were probably formed by ancient lava streams hollowing out large swaths of underground channels under the moon, which eventually hardened as the lava cooled. It's essentially the same process that creates "lava tubes" on Earth, but there's little way of knowing if it's the same process without actually sampling them.
There is most likely an underground cave that widens underground. Image: NASA
That brings us to the question—what now? The next step, Wagner says, is trying to drop a probe into them. If that goes well, maybe we'll be able to set up lunar bases underground someday.
"The ideal follow-up, of course, would be to drop probes into one or two of these pits, and get a really good look at what's down there," Wagner said. "Pits, by their nature, cannot be explored very well from orbit."