Asteroids Act as Water Delivery System to the Moon 4.5 Billion Years Ago, Study Suggests

A new study suggests that internal waters in the moon were most likely to be delivered by asteroids 4.5 to 4.3 billion years ago, as opposed to the widely accepted idea that icy comets delivered water in the inner solar system.

The study, published in the journal Nature Communications, revealed that asteroids, which were previously assumed to be dry due to its molecular structure of clay that locks water inside, crashed into the magma ocean of the moon before it was solidified. The water inside the asteroids was likely to be retained with the help of the thermal lid forming at the surface of the huge magma pool.

"These are asteroids that didn't go through differentiation to have a core, a mantle and a crust like the Earth and the Moon," Dr Jessica Barnes from the Open University in the UK and first author of the study, told BBC. "They contain a lot of water and a lot of organic molecules."

For the study, Dr. Barnes and her colleagues surveyed previously published data for water in lunar samples and bulk estimates of water inside the moon, as well as the available data for the water content and composition asteroids and comets. They also created the model to incorporate different water types.

The researchers discovered that 80 percent of the water in the moon most likely came from asteroids, while the remaining 20 percent came from comets. Additionally, researchers also found out that the water in the Earth has similar composition to the water in the moon, suggesting that the water in our planet also came from crashing asteroids.

The reason why comets only contribute so little water in the moon is because, unlike asteroids, the moon and Earth, comets contain more deuterium, a heavy hydrogen isotope, making it "heavier water.

Their findings shed some light on the origin of water in the inner Solar System. However, researchers stressed out that their study only involved parts of the moon that were explored during different lunar missions.

"But ultimately, we need to explore the entire moon to properly understand it. Our work is timely especially in light of the plans to send robotic and human prospecting missions to previously unexplored regions of the moon," Dr. Barnes wrote in The Conversation.