Makeup of the Moon

New discoveries include the moon's mineral core and a future astronaut city


Jay Melosh looked inside the moon and discovered something surprising about its mineral core, bucking the common understanding that its makeup is similar to Earth’s.

In another study with the Japan Aerospace Exploration Agency (JAXA), Melosh measured a gigantic lava tube on the moon that astronauts could call home. The Distinguished Professor of Earth, Atmospheric, and Planetary Sciences and member of the National Academy of Sciences published these two remarkable lunar studies in October 2017.

Under the surface of the moon

Collision impact on the South Pole-Aitken basin of the moon

Around 4 billion years ago on the far side of the moon, an asteroid collision created the South Pole-Aitken basin — the moon’s largest and deepest impact.

Using remote sensing, Professor Jay Melosh and his research team made a novel discovery when they analyzed the mineral makeup of the splashed-up material and exposed lunar mantle.

“When we look at the spectral signature of rocks exposed deep below the moon’s surface, we see orthopyroxene,” says Melosh, who led the study published in Geology. “The mantle of the Earth is made mostly of a mineral called olivine, and the assumption is usually that all planets are like the Earth.”

The study overturns conventional wisdom about what makes up the interior of the moon, says Melosh, “and, by extension, maybe what makes up the interiors of other planets.”

A possible human habitat

A gigantic lava tube on the moon

Space architects can start envisioning a lunar city — a possible home for astronauts that could shield them from the moon’s atmosphere long-term.

Lava tubes form when lava flow creates a hard crust and a hollow void, and they’re much bigger on the moon than on Earth. The tube in the moon’s Marius Hills recently measured by Professor Melosh at NASA’s Gravity Recovery and Interior Laboratory (GRAIL) could hold all of Philadelphia.

No trip to the moon has lasted more than three days, because spacesuits aren’t sufficient protection against its elements. A co-investigator at GRAIL, Melosh analyzed radar and gravity data from the SELENE aircraft at Japan’s space agency, JAXA, to measure what could be real estate for an astronaut city.

“They didn’t have any idea how far that underground cavity might have gone,” Melosh says. The discovery, published in Geophysical Research Letters, greatly expands possibilities for NASA’s moon research program.