We tend to think of the moon as a dusty, bone-dry place, and for the most part, that's true. But the moon has ice, especially at its south pole, hidden in shady craters. How the ice arrived there was a bit of a mystery, but now a new study suggests that there are different sources, both old and new.
The new results verified by experts were in Icarus [1
This water ice is of great value to both scientists and future human explorers. According to Ariel Deutsch, principal author of the study and doctoral student at Brown University:
The age of these deposits may possibly tell something about the origin of the ice, which helps us to understand the sources and distribution of water in the inner solar system. For exploration purposes, we need to understand the lateral and vertical distribution of these deposits to find out how we can best access them. These distributions change over time, so it is important to have an idea of age.
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The results suggest that not only part of the ice is much older than the rest, but that there are probably other sources as well. Older ice could come from aquatic comets and asteroids or ancient volcanism. Recent ice occurrences could be the result of pea-sized micrometeorites or solar wind implantation.
How did the researchers come to these conclusions?
Using data from NASA's Lunar Reconnaissance Orbiter (LRO), they considered the age of large craters near the Moon's South Pole – like the Shackleton Crater – where ice deposits were found. The age of the craters can be estimated by counting the number of smaller craters in the larger ones. Since scientists have a pretty good idea of the frequency of impacts over time, they can estimate the age of different types of terrain.
Most of the ice is found in very old craters, which formed about 3.1 billion times a year or more, and the ice can not be older than the craters themselves, or it might have evaporated during the impact not that the ice must be the same age as the craters, but it must be old, since the distribution of ice deposits on the crater floors is patchy, suggesting that it has been exposed to impacts of micrometeorites over time.  German added:
There were models of bombardment during the course of d he time that showed ice began to concentrate with depth. So if you have a surface layer that's old, expect more.
What surprised most was ice in smaller, younger craters. This would mean that these ice deposits are also younger and produced by a different process than the ice in the older, larger craters. As German stated:
That was a surprise. In recent cold traps, there had been no real ice observations before.
While spacecraft such as LRO have confirmed the ice deposits – and others, such as India's Chandrayaan-1 mission – to find out how different deposits are likely to form, they will require return missions. Additional robotic missions will come first, hopefully followed by new missions with crew, such as the NASA's planned Artemis mission. If you know exactly where the ice deposits are and how much ice there is, it is important to plan future human missions back to the moon.
Jim Brown, a professor at Brown University, said:
When we think of sending people back to the Moon for long-term research, we need to know what resources we can count on and we do not know at this time. Studies like these help us make predictions about where to go to answer these questions.
Ice on the moon may surprise, but it should not be. Mars has a lot of ice, comets and some asteroids have plenty of ice, there are many moons in the outer solar system that are completely covered in ice crust – with oceans below! – and even Mercury has ice deposits in regions with permanent shadows near its North Pole (as there is no atmosphere to distribute the heat from the sunlit areas). Scientists will now be able to compare the origins of the moon ice with those of other bodies in the solar system. For future researchers, it will be a much needed resource.
Conclusion: Water ice deposits near the south of the Moon According to a recent Brown University study, poles of different ages and backgrounds seem to be.
Source: Analysis of the age of southern polar craters on the Moon: implications for the sources and evolution of surface water ice
Via Brown University