The Japanese space agency JAXA has announced the discovery of a cave hidden beneath the lunar surface. Picked up by Japan's orbiting Selenological and Engineering Explorer (Selene) probe using a special radar sounder system capable of examining underground structures, the enormous cave is thought to be relatively stable and stretches for around 50 kilometers with a width and depth of 50 meters. Scientists believe that the cave, which is thought to be a lava tube formed by volcanic activity 3.5 billion years ago, could contain ice or water deposits along its walls, making it a particularly good location for astronauts to set up a base. "We've known about these locations that were thought to be lava tubes... but their existence has not been confirmed until now," said JAXA senior researcher Junichi Haruyama. "[Lava tubes] might be the best candidate sites for future lunar bases, because of their stable thermal conditions and potential to protect people and instruments from micrometeorites