Fresh research is offering a clearer picture of where water ice might be hiding on the Moon, and the answer could lie in its oldest, darkest craters. Scientists now say that craters near the Moon’s south pole that have remained in shadow for the longest time are the most likely to contain significant amounts of ice. The finding could play a key role in shaping future human missions.
It is not new that some sections of the moon’s southern pole do not receive sunlight. They have been known to be very cold and, therefore, conducive to the survival of ice. But new insights suggest these regions are more dynamic than once believed.
Not all shadows are the same
The idea that the Moon could store ice in shadowed craters dates back to the 1960s. However, when samples were brought back during the Apollo missions, they appeared completely dry. It wasn’t until the 1990s, with missions like the Clementine mission, that signs of water ice began to emerge. Later missions, including Lunar Prospector and the Lunar Reconnaissance Orbiter, strengthened that evidence.
What has puzzled scientists is why ice appears unevenly distributed. Some craters contain strong signals of ice, while others do not.
“What’s clear is that the ice has a patchy distribution,” Paul Hayne, one of the study’s lead researchers, told Space.com. “It’s not concentrated in the same quantities in every crater. And there was no great explanation for that.”
A changing Moon over billions of years
The new study published recently in Nature suggests that the answer lies in the Moon’s long and shifting history. Over billions of years, the Moon’s tilt has changed slightly. This means craters that were once in permanent darkness may have been exposed to sunlight at some point and others may have only recently fallen into shadow.
When sunlight reaches these craters, any ice present can disappear through sublimation, either escaping into space or moving to colder, darker areas. As a result, only the craters that have stayed in shadow the longest have been able to hold onto their ice.
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One such example is Haworth crater, near the south pole, which has remained in shadow for more than three billion years. It also shows some of the strongest signs of water ice.
“It looks like the moon’s oldest craters also have the most ice,” Hayne said. “That implies the moon has been accumulating water more or less continuously for as much as 3 or 3.5 billion years.”
How did the water get there?
The discoveries also contradict the theory that the Moon’s water is a result of only one significant event, for example, a large comet collision with the Moon. Currently, experts assume that the process happened slowly over time.
Among possible explanations are repeated collisions of small comets or asteroids, volcanic activity on the Moon, and solar wind interaction. The interaction of hydrogen with oxygen found on the surface due to the presence of solar wind can lead to the formation of water. Particular quantities of oxygen and maybe water can originate from Earth’s atmosphere.
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What does it mean for astronauts
It was announced during a very crucial period when new expeditions to the Moon, such as Artemis II, show the desire for further research.
Water ice could not be regarded merely as an interesting finding; it will have numerous applications. Water and ice can be utilised by astronauts as water for consumption and oxygen for breathing, which makes their stay on the Moon easier.
One such instrument, the Lunar Compact Infrared Imaging System (L-CIRiS), is set to launch in 2027 as part of a commercial lunar mission.
For now, the message is clear: the Moon’s oldest and darkest corners may hold the key to humanity’s future beyond Earth.
