Leftover SpaceX rocket debris likely slammed into the moon this week, the latest sign of a "lunar litter" problem that could worsen as the U.S. and China race back to the moon.

Leftover SpaceX rocket debris likely slammed into the moon this week, the latest sign of a "lunar litter" problem that could worsen as the U.S. and China race back to the moon.

"Essentially, a mixture of solar activity and gravity forces have put it on a path towards the moon."