Scientists had assumed that the Moon was all done with tectonic activity, because the youngest geological markers on the surface were thought to be about a billion years old.

"It was a big surprise when I spotted graben in the far side highlands," said co-author Mark Robinson, principal investigator of LROC.

"It's exciting when you discover something totally unexpected and only about half the lunar surface has been imaged in high resolution. There is much more of the Moon to be explored."