Lava tubes are naturally occurring channels formed when a lava flow develops a hard crust, which thickens and forms a roof above the still-flowing lava stream.
The safest place to seek shelter is the inside of an intact lava tube, according to the study. These tubes are also found on Earth, but they usually pale in comparison to the size of lava tubes created on the moon which are often large enough to comfortably house an entire USA city. After the flow is stopped and the lava is drained, cylindrical rock formations were left behind.
When JAXA's SELENE spacecraft bounced radar off the area, the data revealed an echo-like signature suggesting the waves were bouncing back off the floor and ceiling of a tube-like structure.
For years, scientists have wondered if dark, crater-like features on the lunar surface might be entrances to giant caverns carved long ago by flowing lava.
The city of Philadelphia is shown inside a theoretical lunar lava tube.
And it just so happens that this area corresponds to locations where NASA, through its GRAIL mission, was able to identify mass deficits-that is, locations on the lunar surface where mass appears to be reduced or missing, which GRAIL detects as slightly less gravity. And it's big-extending for several kilometers in length, and at least one kilometer in height and width.
The Trump administration has expressed interest in returning humans to the moon, with Vice President Mike Pence laying out plans at a meeting of the National Space Council earlier this month.