On Aug. 23, 2023, India’s Chandrayaan-3 lander touched down close to the moon’s south pole, setting in motion an initial 14-day research mission during which a rover named Pragyan will explore our largest satellite.
Slipping between the boulders of the rocky south pole was no small task, though most of the world’s major space agencies are trying to do it. Just a few days before India’s touchdown, a Russian probe crashed into the moon, not far from Chandrayaan-3’s landing spot.
Meanwhile, back on Earth, the China National Space Administration and NASA are gearing up for major unmanned expeditions to the lunar south pole, which has one of the largest supplies of water ice on the moon.
All these world powers want to be the first to discover water ice on the satellite in situ – in its original state – and not as a result of orbital data. With access to water, future moon colonists could slake their thirst or break the molecules down into hydrogen (rocket fuel) and oxygen (good for rocket fuel or breathing).
The good news is that, given the current state of moon science, there is almost certainly water to be found in some areas of the moon. Finding only a dry, old satellite covered in regolith would be a shocker and lead to the reevaluation of decades of influential science.
How Do Scientists Know There Is Water on the Moon?
At first, they guessed.
In 1645, a Dutch astronomer named Michael van Langren drew a map of the moon and labeled the dark patches (those that make up the "man in the moon") maria, Latin for “seas.” That seemed like a plausible explanation until American astronomer William Pickering, after making some telescopic measurements in the late 1800s, concluded that the moon had no atmosphere and any water on its surface would have boiled away a long time ago.
So began the moon-is-dry period, which continued well into the Apollo era, when researchers brought back to Earth some seemingly dry soil samples. However, a theoretical physicist named Kenneth Watson published a paper in 1961 saying a volatile substance such as water could persist on the planet in areas of craters that never receive direct sunlight – places like the moon's south pole. But Watson’s paper would only become influential in later decades.
Read More: No, the Moon Is Not Bigger on the Horizon
Not So Dry After All
Starting in the 1990s, a succession of orbital probes began to produce tantalizing evidence to support Watson’s proposal. In 1998, the Lunar Prospector Mission peered into the shadowed places described by the physicist and found more hydrogen there than elsewhere.
In 2008, the Indian Chandrayaan-1 craft detected signals from the moon consistent with either water or the chemical hydroxide (OH), but unfortunately, couldn’t narrow down the results further.
Two years later, NASA's Lunar CRater Observation and Sensing Satellite (LCROSS) impacted the moon, generating plumes of debris that the Lunar Reconnaissance Orbiter (which launched with and separated from LCROSS) then scanned. The latter found small fragments of ice, confirming Watson almost a half-century later.
Chandrayaan-1’s most dramatic results didn’t reach the public eye until 2018, when data from its NASA-manufactured Moon Mineralogy Mapper revealed large areas of water concentrated at the north and south poles.
While the north side has few spots that remain in permanent darkness, the south has plenty within the large South Pole-Aitken Basin.
New Rover Missions
NASA plans to send a special rover – one of its most sophisticated to date – to the moon’s south pole in late 2024. The Volatiles Investigating Polar Exploration Rover (VIPER) will carry a headlight and sport a 1-meter-long drill to dig into the lunar soil.
The VIPER will venture into darker and more precarious places than any past rover, in its search for water ice. NASA hopes to map ice on Mars and assess how it’s encapsulated on the ground.
China’s Chang’e-7 mission plans to launch in 2026 and deliver a flying probe to the moon, the Water Molecule and Hydrogen Isotope Analyzer. The probe is designed to sample ice and analyze it all on the same craft, much like a rover.