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

A comfy room on the Moon to protect explorers may be a large open lava tube in the Marius Hills region.

That’s the deep dive finding of a new study using radar data collected by a Japanese lunar orbiter — the SELENE spacecraft – and used to detect underlying lava tubes. SELENE was launched in September 2007, and was purposely crashed on the Moon in June 2009.

Japan’s SELENE Moon explorer.
Credit: JAXA

Radar data

A study of the SELENE radar data indicates, near the Marius Hills Skylight, an entrance to the tube, scientists found a distinctive echo pattern: a decrease in echo power followed by a large second echo peak, which researchers believe is evidence of a tube. The two echoes correspond to radar reflections from the moon’s surface and the floor and ceiling of the open tube.

The work has been published in Geophysical Research Letters.

Gravity data

Teaming up with the Japanese researchers, Purdue University experts tapped into data gleaned by NASA’s twin orbiters of the GRAIL mission that collected high-quality data on the Moon’s gravitational field.

Launched as GRAIL A and GRAIL B in September 2011, the probes, renamed Ebb and Flow, operated in a nearly circular orbit near the poles of the moon at an altitude of about 34 miles (55 kilometers) until their mission ended in December 2012, also purposely trashed on the Moon.

NASA’s twin GRAIL probes.
Credit: NASA

Jay Melosh, a GRAIL co-investigator at Purdue University, explains in a press statement: “Our group at Purdue used the gravity data over that area to infer that the opening was part of a larger system. By using this complimentary technique of radar, they were able to figure out how deep and high the cavities are.”

Spacious housing

The city of Philadelphia is shown inside a theoretical lunar lava tube.
Credit: Purdue University/David Blair

The upshot from the subsurface look-sees: Marius Hills is spacious enough to house one of the United States’ largest cities, if the gravity results are correct.

The existence of lava tubes on the Moon has been speculated in the past. But in combining radar and gravity data the result provides the clearest picture of what they look like and how big these features could be.

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