For some decades now, several discoveries have been revealing the presence of water ice on the Moon , in quantities large enough for us to consider using it as a source of liquid water for a future permanent human colony on the surface of our satellite. This ice has various origins , the main one being the bombardment of meteorites rich in water ice during what is known as the “late bombardment”. A new study proposes a new method of acquiring this water, coming from the Earth’s own atmosphere and transported to the Moon by means of the magnetosphere .
Gunther Kletetschka ‘s team , from the University of Alaska in Fairbanks have studied the lunar surface with data from NASA ‘s Lunar Reconnaissance Orbiter and have deduced that a significant amount of the water deposited in the polar regions has a terrestrial origin . Specifically, it would have arrived on board the Earth’s magnetic field, although not in the form of water.
The Earth’s magnetic field , if our planet were isolated in the universe, would have an approximately spherical shape , completely surrounding the Earth, circulating between the poles. However, the Earth is not isolated and orbits around the Sun , which is capable of influencing this terrestrial field through its solar wind. This wind, which consists of charged particles (mainly electrons and protons) that are thrown from the star at high energies, is responsible for the polar lights that we observe on our own and on other planets. It is also responsible for Mars losing much of its atmosphere when its magnetic field was turned off and it is also responsible for the fact that the Earth’s magnetic field is not spherical, but extends in the opposite direction to the Sun , with a drop-like shape. or tear
Therefore the tail of the Earth’s magnetic field extends several hundred thousand kilometers from the planet’s surface , even reaching the orbit of the Moon. This is not unusual, as we know that the tail of Jupiter’s magnetosphere , the largest of any planet in the solar system, can even reach the orbit of Saturn . Well, all this will mean that the Moon will cross this tail of the Earth’s magnetosphere in its orbit around the planet. Specifically, it will do so for about 5 of the 28 days it takes to complete an entire orbit.
Every day, tons and tons of gases escape from the Earth’s atmosphere . Some driven by the magnetic field but others by simple kinetics: due to their temperature, they have too much speed and the planet’s gravitational field is not capable of retaining them . Regardless of how they leave the atmosphere, some of these atoms, especially those that appear in the form of ions , with a certain net electric charge, will be affected by the magnetic field and driven by its lines towards the poles or towards this magnetotail that extends away. of the sun.
This will happen at all times, day and night, winter and summer, and no matter where the Moon is in its orbit. But when the Moon is located inside the magnetotail, the oxygen and hydrogen ions that have escaped from the Earth will be able to deposit on the lunar surface , some of them recombining forming water ice crystals that, with the passage of billions years, they accumulate until they form large deposits . This will be possible because the Moon lacks a magnetic field that can repel these ions, so that the particles will collide with the lunar surface as if it were an interplanetary rain , reaching the surface of the satellite intact.
The authors of the study in question suggest that there could be about 3000 cubic kilometers of ice on the Moon coming from the Earth’s atmosphere through this mechanism. This amount would be approximately equivalent to the water contained in Lake Huron , one of the great lakes located between the United States and Canada, which is the eighth lake in the world in volume of contained water .
This presence of water ice is especially interesting, beyond the purely scientific interest, because it can supply a future human colony on our satellite . These colonies, if they intend to house a certain number of professionals and endure over time, will need to be self-sufficient in their consumption of resources, since currently the prices of sending large quantities of water into space would make these initiatives prohibitive . Not even with the latest-generation reusable rockets could the possibility of transporting all the water necessary for such a project be seriously considered, since currently the cost does not fall below 3,000 dollars per kilogram sent to low Earth orbit.
The Artemis mission that NASA intends to develop in the coming years will study the feasibility of a permanent presence on the Moon for its astronauts, where the availability of water (even in the form of ice) will play a decisive role .
References:
G. Kletetschka et al, 2022, Distribution of water phase near the poles of the Moon from gravity aspects. Sci Rep 12, 4501 https://doi.org/10.1038/s41598-022-08305-x
