New observations have revealed that water on the lunar surface may be more accessible than previously thought. The discovery is particularly exciting for NASA, which hopes to use the Moon’s resources, such as water, in future crewed missions.
In one study, researchers found direct evidence of water molecules in areas of the Moon lit by the Sun. A second study suggests that water ice may occur within small craters and pockets across the Moon’s surface — if this is true, water would be more easily accessible to future missions. Both studies were published in the journal Nature in October.
We already knew there was water on the Moon
Water on the Moon in the form of ice was confirmed by India’s Chandrayaan-1 spacecraft in 2008, but that water is difficult to reach. It occurs mainly in large craters at the Moon’s south pole that are in perpetual darkness. In these areas temperatures plummet to possibly -240 °C making them among the coldest places in the Solar System, and unreachable with current technology. Despite frigid temperatures at the Moon’s south pole, daytime temperatures elsewhere on the lunar surface exceed the boiling point of water. It was previously thought that any water outside of the south pole would have evaporated long ago, but the new research suggests this is not the case.
Speaking to The Verge, Casey Honniball, a postdoctoral fellow at NASA’s Goddard Space Flight Centre and lead author of one of the studies, said: “If we find that [water is] abundant enough in certain locations, it would be easier to access versus going into these very cold, very dark places.”
The water was detected by a flying observatory
Honniball and her team detected water molecules on the lunar surface using the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA), a modified Boeing 747 aircraft equipped with instruments to collect data on objects in space. SOFIA flies above much of Earth’s atmosphere giving the instruments a clear view of the Solar System. The researchers used the observatory’s 2.7-metre reflecting telescope and an infrared camera to pick up the signature specific to water molecules.
The detection of molecular water came as a surprise to the team, who didn’t think that water could survive the high temperatures of the Moon’s daytime. They speculated that the water could be stored within glasses or in voids between grains, protected from the harsh lunar environment and saving it from evaporation.
The second study didn’t detect water directly, but analysed the temperature of mini-craters littering the lunar surface. The researchers used data from NASA’s Lunar Reconnaissance Orbiter to determine that these craters are cold enough for ice to form. In a future Moon mission, these craters would be far easier to reach than the large, dark craters on the south pole. The team estimates that 40,000 square kilometres of the lunar surface can trap water in this way.
There are still many unknowns
While the first study did detect water, only a small amount was found — about 350 ml of water trapped in a cubic metre of lunar soil. And the water will most likely take a lot of work to extract; if the material trapping the water is glass, it will have to be melted to extract the water.
And the second study hasn’t confirmed that there’s water in the cold traps on the surface. Future observations, remote or in situ, will have to examine these in closer detail before we know.
What does this mean for future missions?
The abundance of water across the Moon’s surface broadens the list of places where a lunar base could be established. If the water can be extracted and purified it could be used for drinking and for hydrating plants. Or it could be split into hydrogen and oxygen and used as rocket fuel. Using existing resources on the Moon would reduce the resources that need to be brought up from Earth, saving weight, fuel, time, and money.
NASA and private companies are working to collect more data on lunar water. NASA plans to send a rover called Viper to the Moon in 2023 to map out the locations of surface water ice, and to collect samples. And a private company, Intuitive Machines, plans to send a lander to the surface as soon as 2022, with the same drill as Viper’s, to test the effectiveness of the drill at sampling the water ice. These data, combined with remote observation data, will determine whether or not the water can be used by future astronauts in missions such as those in the Artemis programme.