The surface of the lunar south pole is riddled with ancient craters covered in ice, but how this water first appeared on the moon has long been a mystery. Now, a team of researchers believe these icy pockets could be the result of multiple events that rained down ancient water-bearing objects.
Due to the unique tilt of the moon, its polar regions are permanently shadowed and receive no direct sunlight. Extremely low surface temperatures have helped to preserve the ice, but it is not well understood how it got to the moon in the first place.
To determine the age of the ice, researchers first aged 20 craters found at the lunar south pole using data from NASA’s Lunar Reconnaissance Orbiter (LRO), which has been orbiting and collecting images of the moon for the last decade. Older craters showed more signs of wear around the edges, as well as pockmarks from asteroids or comets that may have struck the surface over time.
“The ages of these deposits can potentially tell us something about the origin of the ice, which helps us understand the sources and distribution of water in the inner solar system,” study lead author Ariel Deutsch in a statement. “For exploration purposes, we need to understand the lateral and vertical distributions of these deposits to figure out how best to access them. These distributions evolve with time, so having an idea of the age is important.”
Most of the ice was found in craters that formed more than 3 billion years ago. Because the ice can’t be older than the crater, the scientists say that the ice is at most the same age. In these older, larger craters, the ice was also patchy due to bombardments from asteroids and comets over time. Newer, smoother ice was found in more recent craters as well. It’s believed that this young ice might have made its way to the moon in a different way than the old ice.
And if the ice is, in fact, different ages, then it means it likely came from two different sources.
But how did it get there? When the moon was still young, it was hit by “relatively high impact rates of comets and asteroids” delivering ice with them, wrote the authors in the journal Icarus. It’s believed that perhaps the older ice found in the ancient craters likely came from this source, whereas the younger ice may have been delivered to the moon either by micrometeorites or through interactions with the solar wind.
But the only way to know for sure is to collect samples from the moon for future analysis.
“When we think about sending humans back to the Moon for long-term exploration, we need to know what resources are there that we can count on, and we currently don’t know,” said study co-author Jim Head. “Studies like this one help us make predictions about where we need to go to answer those questions.”
The Artemis program is set to take off in the next five years, bringing with it the next man and first woman to land on the moon. Perhaps they can shed some metaphorical light on the mystery.