Scientists have long suspected that Earth’s moon holds water. They know that the lunar poles contain hydrogen, which suggests that there’s frozen water there. For decades, researchers have been searching for direct evidence to confirm their suspicions. In a big announcement this week by NASA, researchers announced they’d found evidence of water in regions all around the moon.
In one new paper, researchers used previous knowledge about the moon’s surface to build a 3-D computer model of the orb, and have detected what they think are tiny shadows that may conceal pockets of billion-year-old ice. If proven out by on-the-ground evidence, this discovery could reveal further details about mysteries like how water reached Earth in the first place and why the Moon still has water—and increases the potential for the Moon to one day play a big role in humanity’s quest for space.
“We’ve been searching for ice on the moon for about a decade now,” says Paul Hayne, a professor in the Laboratory of Atmospheric and Space Physics at the University of Colorado at Boulder and a co-author on the study. Most of those efforts focused on the large craters—some as massive as the Grand Canyon—near the lunar poles, which are known to be cold enough to maintain ice.
But in 2014, Hayne and his colleagues were trying to figure out the ice distribution on Ceres, a dwarf planet in the asteroid belt that’s believed to have water trapped on the surface in a similar fashion to what was just identified on the moon. They decided to create a topographic map for Ceres to identify the trapped liquid, when they realized a similar approach would work for the Moon.
The researchers used three data sources that had identified details about the Moon’s surface—a temperature sensing instrument on the Lunar Reconnaissance Orbiter (LRO), a robotic spacecraft currently observing the Moon as well as a camera on the robot and, remarkably, images from the Apollo missions—to build a 3D model of the Moon’s surface and estimate the occurrence of permanently shadowed spots where frozen water could remain. These small spots, known as “cold traps,” range in size from about the diameter of a belly button to much larger craters that could take 10 minutes to walk across. The majority are near the moon’s south pole, and the research team estimates that they could add up to about 15,000 square miles of cold trap.
“In these shadows, the temperatures that we measure with [the LRO] are low enough that water effectively behaves like a rock,” Hayne says. It just sits there, year after year. It’s possible that some of it is billions of years old—which might mean that the oldest water could tell us something about how water got to the Moon, and maybe to Earth, in the first place.
“The cold traps in these permanent shadows are sort of like garbage collectors,” Haynes says, and every time someone lands on the Moon these pockets become slightly contaminated with traces of human presence like rocket fuel. Haynes says that he thinks there should be an opportunity to retrieve samples for scientific research purposes before any planned long-term human trips to the moon.
If all goes according to plan, NASA’s VIPER Lunar Rover mission will land on the moon in 2022 and collect some of these wanted samples. NASA will guide a rover about the size of a golf cart around the southern part of the Moon to take samples for analysis.
“It’ll be great to get the ground truth,” says Sarah Noble, a NASA planetary geologist. The fact that there’s probably frozen water in the tiny shadows of the Moon is “one of those things that’s sort of obvious in retrospect,” she says. After all, we know that water on the Moon has probably ended up there in a variety of ways, and that big cold traps are capable of retaining it.
But “we don’t understand, really, the sources and sinks of those waters,” Noble says. “It might be created from solar winds interacting with the lunar rocks themselves. It might be brought in from asteroids and comets. Some of it might be internal, original water from the Moon itself.”
The frozen Moon water offers tantalizing opportunities for planetary scientists. But it might also make the big business of space travel a little more feasible. Leaving Earth is both expensive and logistically difficult, since you have to get everything out of Earth’s gravitational field. “The hardest part of getting to Mars or the Moon is getting off of the Earth,” says NASA research scientist Jennifer Heldmann.
In recent years NASA and other public and private space entities have started thinking about how space exploration would change if we weren’t limited by resources brought from Earth, but were able to extract needed resources, like water, from space itself.
Companies like United Launch Alliance, Blue Ocean, and SpaceX “would all be interested in finding sources of fuel” on the Moon, says George Sowers, a professor of space resources at the Colorado School of Mines. At least theoretically, Moon water could be mined and then separated into hydrogen and oxygen, with the former being used for fuel.
This approach, called in situ resource utilization (ISRU), would make space exploration cheaper and potentially make it possible to spend more time in space. Water from the Moon’s cold traps could theoretically be transformed into rocket fuel or used as drinking water, for instance.
Pioneering ISRU technologies on the Moon, as NASA has been planning to do on its return to the Moon during the Artemis program, makes sense, says Heldmann. She studies the Moon but also works on planning for an eventual trip to Mars, and she says the Moon is an obvious second home base, because it’s close to develop the technologies to detect, extract and use water from somewhere other than Earth. “These are all the same questions that we have for Mars as well,” she says.
