Scientists discovered water on the moon only a few years ago, and until recently, the prevailing theory was that it got there via comets. Now they're not so sure. New research on rocks brought back from the Apollo 15 and 17 strongly suggests a different possibility: The moon got its water from Earth via meteorites, reports the LA Times. How so? It's widely believed that the moon was formed from debris knocked off Earth by a collision with a Mars-sized body known as the "Big Whack" around 4.5 billion years ago.
It wasn't thought any water survived the impact, but this new study, published in Science, suggests it did—perhaps because the collision formed a barrier of hot gases that protected the water, one of the researchers tells Time. "I'm inclined to think that the measurements, and the primary interpretation, make sense," agreed a scientist who was not part of the study. "[But] this is a piece of the puzzle rather than a solution to the puzzle."