Science has long known that there is ice on the moon, and new research in the journal Scientific Reports shows where some of it came from the Earth’s atmosphere.

Now, most of the Moon’s ice came from the same source as that of Earth – comets and asteroids impacting the surface. According to the study, a minimum of 1% of the Earth’s atmosphere has escaped and been deposited on the Moon. This works out to 3,500 cubic kilometers of ice.

So how did all of this ice get from the Earth to the Moon? It’s a little complicated.

Hydrogen and oxygen ions – molecules with a net electrical charge – escape the atmosphere and follow broken magnetic field lines straight away from the Sun. These field lines often reconnect to form a closed loop around the Earth again. 

At some point in the return portion of this thousands of kilometer journey, these hydrogen and oxygen ions smack into the Moon, which passes through the Earth’s magnetotail for five days of its orbit around Earth. The material forms permafrost in the shadowed portions of the lunar north and south pole and has since the end of the Late Heavy Bombardment. First author Gunther Kletetschka said: It is like the moon is in the shower — a shower of water ions coming back to Earth, falling on the moon’s surface.

More Information

University of Alaska Fairbanks press release

“Distribution of water phase near the poles of the Moon from gravity aspects,” Gunther Kletetshka et al., 2022 March 16, Scientific Reports