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. Researchers from Japan and the United States have uncovered new evidence to prove that these features actually exist—which is good news for future lunar colonists looking for a convenient and safe place to live.

The Marius Hills Skylight, as observed by the Japanese SELENE/Kaguya research team. (Image: NASA/Goddard/Arizona State University)

New research published in Geophysical Research Letters shows that several pits located near the Marius Hill region of the Moon are large open lava tubes, and that these ancient caverns have the potential to offer, in the words of the researchers, a “pristine environment to conduct scientific examination of the Moon’s composition and potentially serve as secure shelters for humans and instruments.” The team, which included scientists from NASA and Japan’s space agency, JAXA, combined radar and gravity data to make the finding.

Our future home? A view of the eastern Marius Hills, with the Marius crater at top right. (Image: NASA/Lunar Orbiter 2)

No doubt, these caverns would be perfect for aspiring lunar colonists. Inside these large holes, humans would be protected from the Sun’s dangerous rays, and other hazards. The Moon has no atmosphere to speak of, so these “instant” shelters would be extremely advantageous.

For years, scientists have suspected that these lunar features were lava tubes—naturally occurring channels that form when lava turns into a hard crust. Millions of years ago, when the Moon experienced volcanic activity, flowing lava carved the surface, and when these channels drained, they oftentimes left a hollow void behind. Previous research showed that these caverns, should they exist, would be stable enough for subterranean lunar bases.

Philadelphia is shown inside a theoretical lunar lava tube. (Image: Purdue University/David Blair)

JAXA scientists analyzed radar data from the SELENE spacecraft, which was designed to study the origins of the Moon and its geological history. As this new study shows, this instrument is also good for detecting lunar lava tubes, which it does by bouncing radar off the lunar surface. By peppering the entrances to these suspected caverns with radar bursts, the scientists were able to detect a distinctive echo pattern, where a decrease in echo power was followed by a second large echo peak. This pattern was the smoking gun, signifying the presence of a floor and a ceiling of a lava tube. Because the scientists found several similar echo patterns at locations nearby, there may be more than one lava tube.

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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.

By combining the SELENE and GRAIL data, the team was able to not just prove the presence of a lava hole, but also the depth and height of the cavity. And it’s big—extending for several kilometers in length, and at least one kilometer in height and width.

Quite suddenly, the Moon seems like a more welcoming place. It’s time for us to go back.

[Geophysical Research Letters]