Space may be the final frontier, but thanks to the way our technology is evolving by leaps and bounds, it’s getting less and less mysterious every single day.

This most recent discovery concerns the South Pole-Aitken Basin on the moon, one of the largest preserved impact craters in the Solar System. The US and China, among others, have been particularly interested in the area, and now NASA’s Gravity Recovery and Interior Laboratory mission has discovered something truly massive beneath it.

The structure weighs 2.18 billion kilograms and stretches more than 186 miles deep, suggesting that it might be leftover from the asteroid that formed the crater, says lead author Peter B. James.

“Imagine taking a pile of metal five times larger than the Big Island of Hawaii and burying it underground. That’s roughly how much unexpected mass we detected.”

The mission was out to measure subtle changes in the gravitational field of the moon, then use the observations to study the moon’s internal composition, but what they discovered was a surprise to everyone involved.

“When we combined that [data] with lunar topography data from the Lunar Reconnaissance Orbiter, we discovered the unexpectedly large amount of mass hundreds of miles underneath the South Pole-Aitken basin. One of the explanations of this extra mass is that the metal from the asteroid that formed this crater is still embedded in the Moon’s mantle.”

The team isn’t sure exactly what they’ve found at this point, though computer simulations indicate it is possible that when an asteroid hit the moon roughly 4 billion years ago it embedded itself in the mantle, never sinking into the moon’s core.

Another theory is that the mass formed when the moon was still solidifying – as the magma of the moon cooled and hardened, perhaps a concentration of oxides may have developed.

More research will follow, but anything we learn from the unique basin should help scientists understand how and when the moon formed, as well as give us an idea as to how it might weather an impact from an asteroid in the future.

And when it comes to space, the more information we have, the better.