Humanity may finally be getting a groundbreaking glimpse of what lies beneath the Moon’s hard outer shell.
According to a study published today in the journal Nature, a Chinese spacecraft has spotted primitive material that might originate from the Moon’s mantle—the layer directly below its rocky crust. The findings await further confirmation, but knowing what lies at the heart of Earth’s satellite could give researchers key insights into the Moon’s inner workings, and help explain how this and other rocky bodies in our Solar System got their start.
Scientists theorize that, during its early days, the Moon was cloaked in an ocean of magma. As the Moon cooled off, it began to solidify, sending materials with lower densities to the ocean’s surface, while heavier minerals sank. This created two chemically distinct layers: a lightweight outer crust, and a thick mantle shrouded beneath.
With the Moon’s crust in the way, tapping into mantle material would require some serious firepower. Luckily, the Solar System’s done the work for us, in the form of impact craters, like the Moon’s South-Pole Aitken basin on the far side of the moon, where China’s Chang’e 4 lander touched down in January to deploy its Yutu-2 rover. The South Pole-Aitken basin, which stretches 1,550 miles wide, was likely formed by a collision so powerful that it punched through the crust—making this cosmic bruise an ideal place to forage for bits of lunar mantle.
“If you’re going to find mantle material anywhere, the South Pole-Aitken basin is the best place to go,” Sara Russell, a planetary scientist at the Natural History Museum in London who was not involved in the study, told Robin George Andrews at National Geographic.
As it scuttled around the basin taking readings of soil, Yutu-2 uncovered material that bore no resemblance to anything else in the lunar crust, including what looked to be two minerals called low-calcium pyroxene and olivine. Both of these substances are rich in iron and magnesium and are relatively dense, making them good candidates for what likely exists in the Moon’s upper mantle.
However, follow-up observations are needed to confirm the minerals’ true identity, Daniel Moriarty, a lunar geologist at NASA’s Goddard Space Flight Center who was not involved in the study, told Andrews. Yutu-2’s data was recorded with a spectrometer, which measure how materials interact with light, and several minerals can emit the same signatures. It’s possible, for instance, that the rover actually uncovered volcanic glass instead of olivine.
One way to resolve the debate may be for Yutu-2 to inspect rocks, rather than mixtures of minerals in soil, Jay Melosh, a planetary scientist at Purdue University who was not involved in the study, told Maria Temming at Science News. Ideally, samples will eventually make their way back to Earth, where they can be more thoroughly analyzed in a lab—which is exactly the goal of China’s upcoming Chang’e 5 and Chang’e 6 missions.
If Yutu-2’s findings are bona fide mantle, however, they could have a whole lot to say. There’s still a lot researchers don’t understand about how the Moon formed and evolved—or even how tectonically active it is today.
What’s more, the Moon is, in many ways, a good proxy for learning about other rocky bodies in the Solar System—including our home planet. Earth might actually have birthed its own satellite when it collided with another massive space rock billions of years ago, jettisoning one particularly hefty piece of cosmic shrapnel into perpetual orbit.
If the Moon is truly a relic of our planet’s distant past, then locked within its enigmatic interior is a timeline of not just its own history, but Earth’s as well. At long last, we may finally be getting our chance to peer inside.