Earth may have helped give rise to water on the moon while shielding it from solar winds.
This defies a leading theory suggesting the moon needs solar radiation to make water.
Understanding how water appears on the moon is crucial to humans living in outer space.
The Earth may have helped give rise to water on the moon, scientists have found.
A cosmic tail of invisible electrons trailing our planet could have generated water on the lunar surface, according to a study published on Thursday.
The finding may help scientists crack the mystery of how water made it to our satellite, and how much water will be available during deep space missions to planets such as Mars.
How does water make it to the moon?
This is the billion-dollar question.
Space agencies and private firms are hatching big plans to take humans away from Earth into our solar system. Having water-rich pit stops along the way is crucially important to these missions so future astronauts can fill up on air, water, and propellants along the way, The Planetary Society said on their website.
This is why the moon has been getting a lot of attention lately: our satellite is about 100 times drier than the Sahara desert, per NASA, but recent research has confirmed that there is water peppered around its surface.
The bulk of the water is mostly seen on the moon's poles in the form of water ice.
There, the water is thought to have come from other planetary bodies — for instance, comets and asteroids that crashed into the surface over billions of years. Another theory is the water was stripped from the Earth as the moon split away.
Most of that water is thought to have since evaporated into space under the sun's intense rays. What's left, then, persists in craters that are permanently in the shadows.
Other research has found that a little water is also created on the moon.
In that case, the leading theory is that water is linked with protons that come from the sun. As solar winds blast the moon's surface, these combine with oxygen in the lunar soil to make water, per The Planetary Society.
But this new finding suggests there could be more to this story.
The Earth could be helping the moon make water
The puzzling new observation, published in the peer-reviewed journal Nature Astronomy, suggests the moon could be making water even when the Earth is shielding it from solar winds.
The Earth is always protecting us from the worst of solar weather. Our planet's strong magnetic field deflects most of the solar particles that come our way.
By re-analyzing data collected between 2008 and 2009 by India's Chandrayaan-1 mission, scientists spotted that some water was being created on the moon when it was crossing the Earth's magnetotail, a sheet of plasma trapped between magnetic fields stretched outwards by the solar winds skimming our planet.
Notably, solar winds in the magnetotail are reduced by as much as 99%, per the study.
The findings raise an interesting proposition: If even a little water can be generated when solar winds are virtually gone, do you need the solar winds to make water on the moon?
Per the scientists, it's possible the high energy electrons in the magnetotail could have "similar effects as the solar wind protons" when it comes to creating water, Li said in the statement.
"We suggest that although we have confirmed the importance of the solar wind as a major source of fast water production on the moon, hitherto unobserved properties of the plasma sheet" could play an important role, the scientists said in the study.
The findings add to the many theories that are seeking to explain water on the lunar surface.
Li and colleagues aim to work with NASA to monitor plasma and water content on the lunar surface to see if their theory checks out.
If confirmed, this could have wider-reaching implications, particularly with regard to water found in the moon's shadowy craters, scientists said in an accompanying press release.
If you don't need the sun to create water on the moon, it's possible the water seen in these craters doesn't have to have come from comets. It could have been generated in situ.
"This provides a natural laboratory for studying the formation processes of lunar surface water," said Li.
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