(CNN) – Astronomers are scratching their heads over a huge lump beneath the moon’s surface.
They say it’s about five times larger than Hawaii’s Big Island.
But scientists at Baylor University, who discovered the mass, aren’t sure what it is.
It lies at the bottom of a huge crater, located on the far side of the moon, that was created by an asteroid impact about 4 billion years ago.
One theory is the mass is metal left over after the impact.
If that’s true, the mass would be a gold mine for scientists exploring the history of our solar system.
The discovery was published in the journal “Geophysical Research Letters.”