Deep and shaded Shackleton crater near the southern pole of the moon is a site where researchers have found deposits of water ice. The ice has the potential to reveal insights about the history of the moon and our solar system. And it can be useful for future lunar explorers. Image via NASA / Goddard Space Flight Center / Leonard David's Inside Yuter Space.
We tend to think of the moon as a dusty, bent dry place, and for the most part it's true. But the moon has ice, especially at its south pole, hidden in shaded craters. Exactly how the ice got there has been a bit of a mystery, but now a new study suggests that it can have different sources, both old and newer.
The new peer-reviewed findings were published Icarus on September 30, 201
This water ice has great value, both for researchers and future human explorers. According to Ariel Deutsch, lead author of the study and a doctoral student at Brown University:
The ages of these deposits can potentially tell us something about the origin of ice, which helps us understand the sources and distribution of water in the inner solar system. For exploration purposes, we must understand the lateral and vertical distributions of these deposits to find out how to best access them. These distributions develop over time, so it's important to have an idea of the age.
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Map of known water ice deposits near the lunar south pole, from NASA's Lunar Reconnaissance Orbiter (LRO). Image via NASA / Goddard Space Flight Center / AmericaSpace.
The results indicate that not only is part of the ice much older than the rest, but that there are probably also different sources. Older ice could have come from water-carrying comets and asteroids or ancient volcanism. Newer ice deposits may be the result of pea-sized micrometeorites or implantation of solar wind.
So how did the researchers come to these conclusions?
Using data from NASA's Lunar Reconnaissance Orbiter (LRO), they looked at the ages of large craters near the lunar south pole – for example, the Shackleton crater – where ice deposits have been found. The age of the craters can be estimated by counting the number of smaller craters in the larger ones. Because researchers have a pretty good idea of the speed of effects over time, they can estimate the ages for different types of terrain.
<img aria-describedby = "caption-attachment-323085" class = "wp-image-323085 size-large" src = "https://en.es-static.us/upl/2019/10/Chandrayaan -1-moon-ice-map-800×495.jpg "alt =" 2 images of cratered moon surface: Gray on left and red-blue false color on right.
<img aria-describedby = "caption-attachment-323085" class = "wp-image-323085 size-large" src = "https://en.es-static.us/upl/2019/10/Chandrayaan-1-moon-ice-map-800×495.jpg" alt = "19659016] India's spacecraft Chandrayaan-1 also found evidence of ice sets on the moon back in 2009. Image via Indian Space Research Organization (ISRO) / Discover.
Most of the ice is found in very old craters, formed about 3.1 billion years ago or more. The ice can't be older than the craters themselves, or it would have evaporated under the bumps. This does not mean that the ice must be as old as the craters, but it must be old because the distribution of the ice deposits on the crater floor is uneven, suggesting that it has been subjected to the influence of micrometeorites for a long period of time.
There have been models of bombardment over time that show that ice is starting to concentrate with depth. So if you have a surface layer that is old, you can expect more underneath.
What was most surprising was ice in smaller, younger craters. This would mean that these ice deposits are also younger and were created by a different process than the ice in the older, larger craters. As Deutsch noted:
It was a surprise. No observations had actually been made of ice in younger cold traps before.
While spaceships like LRO have confirmed the ice sets – and others, as well as India's Chandrayaan-1 mission, too – to figure out how different deposits actually formed will probably require return missions. Further robotic missions will first, hopefully, be followed by new crew missions such as NASA's planned Artemis mission. Knowing exactly where the ice deposits are and how much ice it is will be important for planning future human missions back to the moon.
Future human missions to the moon, such as NASA's planned Artemis mission, will need resources such as water ice deposits to maintain a long-term presence. Image via NASA.
Jim Head, a professor at Brown University, explained:
As we consider sending people back to the moon for long-term exploration, we need to know what resources are there that we can count on, and we currently do not know . Studies like this help us make predictions about where we need to go to answer these questions.
Ice on the moon may seem surprising, but it shouldn't be; Mars has lots of ice, comets and some asteroids have plenty of ice, there are many moons in the outer solar system completely covered by an ice crust – with oceans below! – and even Mercury has ice deposits near its north pole, in regions with permanent shade (since there is no atmosphere to distribute heat from the sunlit areas). Researchers will now be able to compare the origin of the lunar ice with other bodies in the solar system, and for future explorers it will be a much needed resource.
Bottom line: Water deposits near the south pole of the moon appear to have different ages and have different sources, according to a new study from Brown University.
Source: Analyzing the ages of southern polar craters on the moon: Implications for the sources and evolution of surface water ice
Via Brown University