The return of humans to the moon, as well as ongoing robotic missions, may require using resources already on the lunar surface. The moon's south pole is of particular interest because of ice deposits in craters there.
Unfortunately, India's Chandrayaan-2 lunar mission lost communication while attempting to soft land a rover on the moon's south pole. But NASA's Lunar Reconnaissance Orbiter has been orbiting the moon since 2009 and mapping the south pole region.
Scientists want to understand how the ice deposits initially formed in the craters. Because the moon has no atmosphere, it's constantly impacted by objects like meteorites and micrometeorites. This helps researchers to understand lunar history as well as identify resources for future missions.
A new study identifying the ages of the ice deposits published Thursday in the journal Icarus. The researchers used Lunar Reconnaissance Orbiter data to determine that many of the deposits are billions of years old, bur some of them are more recent.
"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," said Ariel Deutsch, a study author and a graduate student at Brown University's Department of Earth, Environmental and Planetary sciences. "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."
Researchers can figure out the age of the ice by identifying the age of the craters themselves. Older, large craters will contain smaller craters on the inside, leaving clues for scientists to determine how many impacts have occurred since the larger hit that created the initial crater.
Many of the large craters were created about 3.1 billion years ago, or possibly older. This means the ice is just a bit younger than that. In some craters, the ice is patchy because it's been hit by other debris over time.
"There have been models of bombardment through time showing that ice starts to concentrate with depth," Deutsch said. "So, if you have a surface layer that's old, you'd expect more underneath."
The older ice likely came from comets and asteroids that carried water with them when they hit the lunar surface.
Smaller craters also contained ice. These craters were more well defined and looked much fresher, which suggests that the craters and the ice are younger, the researchers said.
"That was a surprise," Deutsch said. "There hadn't really been any observations of ice in younger cold traps before."
The small craters were likely formed by micrometeorites. Future missions could take a closer look at these craters and determine more details.
"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," Head said. "Studies like this one help us make predictions about where we need to go to answer those questions."