(CNN) Here is something you may not know about the moon: Earth's clingy best friend is also the site of one of the largest-known impact craters in our entire solar system. Essentially, something caused a giant hole on the moon billions of years ago, and astronomers have just discovered that there's something big -- really big -- buried underneath the surface.

The colored image shows the South Pole-Aitken basin in blue, and the location of the mass under the surface is circled.

According to research published in the journal "Geophysical Research Letters," the moon's South Pole-Aitken basin hides a mass that is estimated to be 4.8 quintillion pounds (that's -- are you ready for it? -- 4,800,000,000,000,000,000 pounds, all written out).

"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," author Peter B. James said in a release

The researchers from Baylor used various sets of data collected from space crafts that measure the gravity around the moon, and compared them to maps and imaging of the moon's surface. As a result, they found a dense metallic mass pulling down on the floor of the basin.

So, what is it? James and his team surmise it could be metal embedded in the moon's mantle from the asteroid impact that caused the crater some estimated 4 billion years ago. If that's true, it could be a time machine -- and a gold mine -- for scientists studying the history of the universe. All of that metal, and basically the entire area surrounding the mass and the crater, could tell them a lot about how the asteroid impact happened and what the solar system was like when it did.

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