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We are peeking under the moon’s crust for the first time. The Chinese Yutu 2 moon rover, which landed in January aboard the Chang’e 4 lander, has spotted what appears to be primitive material from the moon’s mantle, which may help reveal details about its early magma ocean.

Chang’e 4 landed on the far side of the moon in the South Pole-Aitken basin, the moon’s largest impact crater at about 2500 kilometres across. Simulations have shown that the collision that created this crater was probably powerful enough to punch through the moon’s outer crust, revealing rocks from its interior.

Chunlai Li at the Chinese Academy of Sciences in Beijing and his colleagues examined data that Yutu 2 took during its first day on the moon looking for those deeper rocks. They seem to have found them in an area of material tossed from another smaller crater within the basin.

The lunar soil that Yutu 2 examined contained relatively heavy minerals rich in iron and magnesium. Early in the moon’s history, when it was covered in a magma ocean, these heavier minerals would have sunk while lighter silicates floated and eventually solidified into the crust.

“This is the first ground truth of what the interior of the moon is really made of,” says Briony Horgan at Purdue University in Indiana. “I would say the really important thing is that it’s different from the Earth.” This difference may be because of how water changed Earth’s mantle early in its history, she says.

“The ultimate goal is to decipher the mystery of the lunar mantle composition,” says Li. This will help uncover how the moon’s magma ocean evolved, which may be useful for studying other bodies, like Earth, that had magma oceans but whose surfaces have changed much more since then.