In 2009, scientists confirmed there was water on the moon, but had no idea how it got there.
A new study concludes that asteroids probably carried water to the moon about 4.5 billion years ago, according to research published in the journal Nature Communications.
Back when Neil Armstrong and Buzz Aldrin walked the moon, we didn't even know the water existed. It's only present in small quantities below the surface, and our instruments at the time weren't sensitive enough to detect it. Later, after our techniques advanced, scientists discovered traces of water in the lunar samples that the Apollo astronauts brought back to Earth.
Then scientists had to figure out where it came from.
How water ended up on the moon: For the study, scientists compared the composition of the moon to asteroid and comet samples. They concluded that most — over 80% — of the water in the moon's interior was acquired from asteroids that pummeled the lunar surface billions of years ago.
This was a really violent period in our solar system's history, which means that Earth was probably getting slammed with water-carrying asteroids too, according to the study.
"Our work, therefore, confirms that the inner Solar System received a similar flux of asteroidal and cometary material for much of its early history," the researchers concluded.
Who knows where else we'll find water?