The uncertainty of science: New research of the craters where ice is suspected to exist on the Moon suggests that the ice is found in both young and old craters, which also suggests both that it comes from multiple sources and that some has been deposited more recently.

The majority of the reported ice deposits are found within large craters formed about 3.1 billion years or longer ago, the study found. Since the ice can’t be any older than the crater, that puts an upper bound on the age of the ice. Just because the crater is old doesn’t mean that the ice within it is also that old too, the researchers say, but in this case there’s reason to believe the ice is indeed old. The deposits have a patchy distribution across crater floors, which suggests that the ice has been battered by micrometeorite impacts and other debris over a long period of time.

If those reported ice deposits are indeed ancient, that could have significant implications in terms of exploration and potential resource utilization, the researchers say. “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.”

While the majority of ice was in the ancient craters, the researchers also found evidence for ice in smaller craters that, judging by their sharp, well-defined features, appear to be quite fresh. That suggests that some of the deposits on the south pole got there relatively recently. “That was a surprise,” Deutsch said. “There hadn’t really been any observations of ice in younger cold traps before.”

If there are indeed deposits of different ages, the researchers say, that suggests they may also have different sources. Older ice could have been sourced from water-bearing comets and asteroids impacting the surface, or through volcanic activity that drew water from deep within the Moon. But there aren’t many big water-bearing impactors around in recent times, and volcanism is thought to have ceased on the Moon over a billion years ago. So more recent ice deposits would require different sources — perhaps bombardment from pea-sized micrometeorites or implantation by solar wind.

I must emphasize that there is much uncertainty here. Most fundamental is the fact that at this moment we still really do not have a solid confirmation of the presence of ice in these permanently shadowed craters, only orbital data that suggests the presence of hydrogen, which scientists believe can only be there if it is locked in water molecules. This is not yet proven however.

It is intriguing however the evidence suggests ice in both young and old craters. This implies either some on-going process to put water there, or a series of specific but different events over time.