How did water molecules and ice arrive to the Moon in the first place? Some of it is thought to have originated through asteroid and comet impacts, but a recent research proposes another source of lunar water: the Earth's atmosphere.
According to experts, hydrogen and oxygen ions escaping from Earth's upper atmosphere and mixing on the Moon might have formed up to 3,500 cubic kilometers (840 cubic miles) of surface frozen or beneath liquid water.
As the Moon travels through the Earth's magnetosphere's tail, hydrogen and oxygen ions are thought to be pushed into the lunar surface (the teardrop-shaped bubble around Earth affected by its magnetic field). Every lunar month, this happens five times.
Some of Earth's magnetic field lines are broken, only linked to the planet at one end, due to the Sun's solar wind pressing against this bubble.
When the Moon collides with the Earth's magnetosphere's tail, some of these broken connections are repaired, causing hydrogen and oxygen ions to rush back into the atmosphere that had previously escaped.
"It's like the Moon is showering — a shower of water ions returning to Earth and dropping on the Moon's surface," says Gunther Kletetschka of the University of Alaska Fairbanks.
The researchers believe that these ions have slowly accumulated over billions of years since the Late Strong Bombardment, a period when the early Earth and Moon were bombarded with heavy impacts from other celestial things racing across space.
The Moon's polar regions and numerous prominent craters were studied using gravitational data from NASA's Lunar Reconnaissance Orbiter. The scientists discovered anomalies that might suggest permafrost-trapping rock cracks.
"Crater impacts, which generate structural extensions and fractures," the researchers write in their report, "provide ideal pore space networks for hosting huge subterranean liquid water reservoirs."
"Back of the envelope estimates showed that during the previous 3.5 billion years, several thousands of cubic kilometers of water phase may have accumulated this way into the Moon's subsurface."
While the water on the Moon is thought to come from a variety of sources, including hydrogen and oxygen processes caused by solar winds, a large portion of it may have arrived by this way.
The estimated buildup would be enough to fill North America's Lake Huron. Craters and rock cracks would then offer the required protection to keep the water from evaporating back into space.
NASA wants to establish a long-term human presence on the Moon, which will require a viable lunar outpost with a nearby water source. This new study might aid specialists in deciding where to locate the station.
"Water ions that formed many millennia ago on Earth can be utilized in the astronauts' life support system," adds Kletetschka, as NASA's Artemis team prepares to create a base camp near the Moon's south pole.
