Here on Earth, we take from the moon countless myths, legends and mysteries. We give it, in return, a bunch of high-energy electrons from our magnetosphere’s plasma sheet. But this is not such a piddling gift, according to a new paper, which proposes that these electrons react with the moon’s surface to create water.
Scientists have long presumed that the solar wind – an outpouring of particles from the sun – creates water on the moon. In doing so, it has joined impacts from icy comets and meteorites in adding the compound to our largest satellite.
Water on the moon has become a very big business since both U.S. and China plan to send rovers to Luna to sample it firsthand. With the right technology, water can be broken down to oxygen and hydrogen, components of rocket fuel. Astronauts could drink it, too, making it one of the most useful molecules for a space mission.
Is There Water on the Moon?
Scientists have gathered strong evidence that substantial water reserves exist at the north and south poles of the moon, within craters that shield them from the sun.
For decades, experts had assumed that no water could survive on the satellite, but U.S. and Indian space probe missions have provided evidence to the contrary. Starting in the 1990s, they detected evidence of water in craters, most likely in the form of ice.
Then in 2018, data from the NASA-manufactured Moon Mineralogy Mapper (an instrument on board India's Chandrayaan-1) revealed a detailed map of water on the body, which is estimated to hold 240,000 Olympic swimming pools of the stuff.
How the Magnetotail Creates Lunar Water
Because Earth’s core serves as a dynamo, the planet enjoys the protective power of a large magnetosphere that wraps around the globe and deflects the solar wind. All that energy must go somewhere, however, and much of it ends up on the dark side of the planet within a long tail. According to this paper, the “magnetotail” contains both an ionic plasma sheet and another filled with electrons.
When the moon is full, the magnetotail crosses over the moon and bombards it with electrons, especially in darkened areas where it doesn’t have to compete with photons. This crossover period lasts for about a week, according to NASA, while the tail lashes back and forth across the surface of the moon.
Right then, the satellite is shielded from the solar wind, a handy fact for the researchers wanting to test the effects of the tail alone.
Other New Evidence of Water on the Moon
Researchers looked to data collected in 2008 and 2009 by the Moon Mineralogy Mapper instrument onboard India’s Chandrayaan 1 space probe, which had data from full moons. The team found that even in the absence of the solar wind, the moon continued to create new water.
“Water formation was expected to drop to nearly zero,” said Shuai Li, an assistant researcher in the University of Hawai'i at Mānoa School of Ocean and Earth Science and Technology, in a statement. “To my surprise, the remote-sensing observations showed that the water formation in Earth’s magnetotail is almost identical to the time when the Moon was outside of the Earth’s magnetotail.”
Electrons in the tail seem to do the same work as protons in the solar wind, Li proposes. This may help to explain the accumulation of ice within the shielded craters of the moon’s north and south poles.
Read More: What's So Great About the Moon's South Pole?