The cavern, found in the Marius Hills area on the near side of the moon, is about 100 meters wide and extends for about 50 km, according to data taken by JAXA's Selenological and Engineering Explorer (SELENE), also called the Kaguya moon probe.
In 2009, the Kaguya probe found a large shaft with an opening about 50 meters in diameter in the Marius Hills area. The shaft descends about 50 meters beneath the surface.
The cave would have about 2 square miles of space. With urban population density, this cave could hold 100,000 people.
The JAXA team analyzed data obtained from a lunar radar sounder on the probe that indicated an underground structure extended west from the shaft.
If future lunar explorers could use the underground space for a base, it could provide shelter from cosmic radiation and menacing temperatures, while water or ice could be used as fuel, the JAXA team said.