Astronomers have discovered large holes on the moon — indicating a possible tunnel network underneath the lunar surface, BGR is reporting.

The lunar holes were found near the moon's north pole by researchers working with the SETI Institute and Mars Institute, according to the website. The researchers used images from NASA's Lunar Reconnaissance Orbiter to spot the holes.

The tunnels are believed to be what is left of ancient lava tubes, where liquid rock had once flowed, BGR reported. At some point, the flow stopped and all the holes on the surface remained.

The holes are suspected "skylights," where the shell of the lava tube collapsed and pushed a path onto the surface, BGR said.

"The highest resolution images available for Philolaus Crater do not allow the pits to be identified as lava tube skylights with 100 percent certainty, but we are looking at good candidates considering simultaneously their size, shape, lighting conditions and geologic setting" said Pascal Lee, a scientist with the SETI Institute.

It is uncertain how large the tunnels actually are, but astronauts could possibly use them as a shelter to protect themselves and some of their equipment from space radiation, BGR reported.

This new report supports the findings last fall of a group of Japanese scientists, who confirmed the existence of a 31-mile-long cavern believed to a lava tube created 3.5 billion years ago. The cavern is located under an area called Marius Hills.