There is no doubt that the moon has water on its surface. Orbiters have seen deposits of ice persisting in the eternal shadows of polar craters. And recent research shows that water also exists in sunlight parts of the Moon.
Over the years, scientists have presented evidence that the moon’s water comes from comets, asteroids, from within the moon and even from the sun.
But now new research is pointing the finger directly at the earth as the source of some of the moon’s water.
The new study is titled “Earth Wind as a Possible Exogenous Source of Moon Surface Hydration.” The lead author is HZ Wang of Shandong University in China, and the article is published in The Astrophysical Journal Letters. The research suggests that particles from the earth can sow the moon with water.
That the moon has water is not surprising. Astronomers have found water in all sorts of places in space, although it is mostly ice. The prevailing theory for water is that it arrives on planets and moons as they form, perhaps produced by asteroids or comets. But this article contains evidence that some of the water on the lunar surface comes from the earth’s wind.
It is likely that the solar wind is responsible for some of the surface water of the Moon. The lunar regolith contains silicates, and protons in the solar wind can reduce the oxygen from the silicates. That oxygen is then easily combined with hydrogen to form water.
The problem with the sun as the only source of lunar surface water is evaporation. Computer models predict that a large portion of it – up to 50% – will have to evaporate from high regions of the lunar surface during the full moon. Three to five days into each cycle, the moon is in the Earth’s magnetosphere, which means that water must disappear from the surface, as the Earth’s magnetosphere blocks the solar wind to reach the Moon and replenish the surface water during that period.
But that’s not what’s happening. Instead, according to data from the Indian Chandrayaan-1 satellite’s Moon Mineralogy Mapper, the water does not disappear during full moons. The authors of the study say that an ‘Earth Wind’ complements this.
The solar wind and the earth wind differ from each other. The solar wind is mainly plasma consisting of protons and electrons released from the upper atmosphere of the sun. But the earth’s wind is a flow of ions from the magnetosphere, measured by the THEMIS-ARTEMIS mission.
The Kaguya mission in Japan detected hydrogen ions from Eath’s exosphere in the ground. It also observed high concentrations of oxygen isotopes coming from the earth’s ozone layer and embedded in the lunar surface. This indicates the idea of a ‘water bridge’ from the earth to the moon. This bridge is active during the days of the month when the Moon is inside the Earth’s magnetosphere, and it replenishes the water that has evaporated due to evaporation.
Although these findings are very helpful in explaining lunar surface water, they may also be of greater importance. If there is a bridge between the earth and the moon that creates water on the moon, where else in the solar system can this happen?
The authors proposed a mechanism for lunar water that co-existed with the solar wind declaration. But this has not yet been confirmed. Future studies may provide further evidence that there is a water bridge between the earth and the moon. China’s Chang’e 5 mission brought lunar monsters back to Earth in December. These samples may contain evidence for the idea of the water bridge.
If this turns out to be correct, astronomers will immediately begin to wonder (they probably already have) whether a similar mechanism is at work elsewhere, perhaps here in our own solar system.
This study also shows how much more we need to learn about the interactions between planets, their moons and their stars. The evolution of water in us and other solar systems may depend on these interactions. This research effort can also help us understand the potential habitability of distant exoplanets.