UAF Researchers Probe Origin of Lunar Water

Kletetschka and his colleagues suggest hydrogen and oxygen ions are driven into the Moon when it passes through the tail of the Earth’s magnetosphere, which it does on five days of the Moon’s monthly trip around the planet. The magnetosphere is the teardrop-shaped bubble created by Earth’s magnetic field that shields the planet from much of the continual stream of charged solar particles.

Recent measurements from multiple space agencies—NASA, European Space Agency, Japan Aerospace Exploration Agency, and Indian Space Research Organization—revealed significant numbers of water-forming ions present during the Moon’s transit through this part of the magnetosphere.

These ions have slowly accumulated since the Late Heavy Bombardment.

The presence of the Moon in the magnetosphere’s tail, called the magnetotail, temporarily affects some of Earth’s magnetic field lines—those that are broken and which simply trail off into space for many thousands of miles. Not all of Earth’s field lines are attached to the planet at both ends; some have only one attachment point. Think of each of these as a thread tethered to a pole on a windy day.

The Moon’s presence in the magnetotail causes some of these broken field lines to reconnect with their opposing broken counterpart. When that happens, hydrogen and oxygen ions that had escaped Earth rush to those reconnected field lines and are accelerated back toward Earth.

The paper’s authors suggest many of those returning ions hit the passing Moon, which has no magnetosphere of its own to repel them.

“It is like the Moon is in the shower—a shower of water ions coming back to Earth, falling on the Moon’s surface,” Kletetschka says.

The ions then combine to form the lunar permafrost. Some of that, through geologic and other processes such as asteroid impacts, is driven below the surface, where it can become liquid water.

The new research estimates the Moon’s polar regions could hold up to 3,500 cubic kilometers—840 cubic miles—or more of surface permafrost or subsurface liquid water created from ions that escaped Earth’s atmosphere. That’s a volume comparable to North America’s Lake Huron, the world’s eighth-largest lake.

Researchers based that total on the lowest volume model calculation—1 percent of Earth’s atmospheric escape reaching the Moon.

The research team used gravitational data from NASA’s Lunar Reconnaissance Orbiter to study polar regions along with several major lunar craters. Anomalies in underground measurements at impact craters indicate locations of fractured rock conducive to containing liquid water or ice. Gravity measurements at those subsurface locations suggest the presence of ice or liquid water, the research paper says.

The latest research builds on work published in December 2020 by four of the new paper’s authors, including Kletetschka.

Finding water is key to NASA’s Artemis project, the planned long-term human presence on the Moon. NASA plans to send humans back to the Moon this decade.

“As NASA’s Artemis team plans to build a base camp on the Moon’s south pole, the water ions that originated many eons ago on Earth can be used in the astronauts’ life support system,” Kletetschka says.