Ten underground tunnels that once contained flowing lava may have been discovered on the Moon. These 'lava tubes' are hollow structures that scientists believe could be used to provide shelter for the first lunar settlers.
The findings were presented at the 47<sup>th Lunar and Planetary Science Conference. The scientists said their results showed the strongest evidence yet that there are empty lava tubes on the Moon.
Lava tubes are giant caverns, buried under the surface of Earth. Volcanic lava once flowed easily underground, but the cooler lava on the outside of the flow solidified – making tunnels. Once lava flow completely stopped, these caves became empty. Researchers have suggested the tunnels could also exist on the Moon, as its volcanic activity was once similar to Earth's.
Up until now, scientists have only been able to use slight surface features to look for the tunnels.
Researchers from Purdue University used data from Nasa's GRAIL spacecraft to examine the Marius Hills region of the moon – a region of volcanic domes.
The spacecraft detected anomalies in gravity, caused by the giant underground caverns. Large masses increase gravity on the Moon. Likewise, any giant tunnels would reduce the gravity, and a dip would be recorded.
This data was then analysed to show 10 potential lava tubes beneath the surface, all around 125m wide. While these are not big enough to support humans, the researchers suggest they could open up to much wider caverns.
To find out, the researchers suggest using a Moon-orbiting robot to investigate whether these tubes exist. The robot would use underground sounding radar to map the Moon's interior.
"The proposed radar will not only help confirm our findings but will also give us an opportunity to find smaller lava tubes, ones that were beyond the resolution of GRAIL gravity data," Rohan Sood, co-author of the research, told National Geographic.
The researchers also said lava tubes could provide a safe environment for humans to form settlements on the Moon. Their thick roofs could protect humans from radiation and meteorite impacts.