Potential patches of Earth's ancient crust, sometimes called "sunken worlds," may have just been discovered deep within the mantle, thanks to a new way of mapping the inside of our planet.

Artist’s conception of the K2-360 system, showing the ultra-dense super-Earth K2-360 b (red) in its extremely close orbit around its Sun-like star, with the more distant companion K2-360 c (blue) in ...