New research has revealed that the surface of the moon was rich with water around 4 billion years ago.
The research could be an important step towards better understanding the evolution of the moon and could also help inform future moon missions, including NASA's Artemis 3, which aims to return humans to the lunar surface no sooner than 2026 and leverage frozen water found there for a sustainable presence on the moon.
University of Western Ontario postdoctoral fellow Tara Hayden was investigating a lunar meteorite, which was once a piece of the moon's surface, when she discovered it contained the mineral apatite. This common phosphate allowed for a direct examination of an unknown stage in lunar evolution for the first time when the moon was molten.
The study of the meteorite shows that the crust of the moon contained more water back in ancient lunar history than scientists had previously believed. "The discovery of apatite in the moon's early crust for the first time is incredibly exciting — as we can finally start to piece together this unknown stage of lunar history," Hayden said in a statement. "We find the moon's early crust was richer in water than we expected, and its volatile stable isotopes reveal an even more complex history than we knew before."
Apollo lunar samples didn't paint the full picture of moon water
Hayden explained that the examination of lunar meteorites such as the one she studied to find apatite is important in learning more about the moon and could perhaps reveal insights not found in the samples brought back to Earth in the 1960s and 1970s as part of the Apollo program.
When the Apollo lunar samples were first examined, scientists found they were "volatile-poor." Volatiles are chemicals that easily evaporate at relatively low temperatures; water is moderately volatile, evaporating at 212 degrees Fahrenheit (100 degrees Celsius). This led to the assumption that the moon was "bone dry."
That assumption was challenged in 2008 when scientists found significant amounts of water and volatiles in glass beads in the Apollo samples, prompting another look at them. As that study proceeded over the last 15 years, other samples such as lunar meteorites that had rained down on Earth after being freed from the moon's surface by asteroid strikes and other impacts have shown the moon has been anything but bone-dry during its history.
"We know most about the history of water on the moon from the Apollo samples, but those samples are thought to only represent about five percent of the entire moon surface," Hayden said. "Until we get more samples back in the upcoming Artemis missions, the only other samples from the surface we have are meteorites."
While studying one of these lunar meteorites during her studies at the Open University in the U.K., Hayden found it held key information about water on the moon that she says is "so vital to our understanding about lunar water-bearing minerals."
Hayden focused primarily on the mineral apatite, which contains volatiles in its mineral structure, finding it within "ferroan anorthosites" in the sample. Ferroan anorthosites are the only known lunar rocks that formed directly from the Lunar Magma Ocean, a slushy sea of molten rock that existed on the surface of the moon 4.5 million to 4.3 million years ago.
Finding this volatile-rich element in the ferroan anorthosite indicates water was present in the moon's mostly molten stages and allowed researchers to study this stage of the moon's evolution directly, the first time this had been done.
"Unraveling the history of water in the earliest-formed lunar crust approximately 4.5 billion years ago is important for improving our understanding of the origin of water in the solar system," Open University professor of planetary science and exploration Mahesh Anand said. "Ancient rock samples from the moon in the form of lunar meteorites provide an excellent opportunity for undertaking such investigations."
Hayden's discovery comes at a crucial time for moon science as humanity gears up to return to the moon for the first time in 50 years via Artemis and as longer lunar stays loom on the horizon.
Frozen water on the lunar surface could be used during future missions not only to sustain astronauts but also to extract hydrogen for fuel that could be used to return teams back to Earth or could be employed for trips deeper into the solar system, such as to Mars.
"It has been long believed the lunar surface has been dried out for thousands and even millions of years, but maybe there might be more water available than we thought on the surface of the moon, and we just need to find a way to extract it," Hayden said.
These new lunar rock revelations are described in a paper published in Nature Astronomy.
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Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.
Timeline is difficult to follow, as there are several references to the crust drying out thousands of years ago, millions of years ago, and alternately, billions of years ago.Reply
As far as I can tell, the events referenced pertained to the earliest periods in the lunar geological timescale, ~4.0-4.5B years ago. The reference to recent events occurring on the order of mere thousands of years ago confuses me. I can't find anything regarding significant lunar geological changes occurring, including loss of water/volatiles, in the past few million years.
Makes sense if the Moon was orbiting around the Earth at the time of the Late Heavy Bombardment. It probably would have collected a significant amount of water from that, just as the Earth did (theoretically).Reply
From the paper supplement:Reply
The relatively high H2O abundance (~ 2300ppm) is greater than observed in Apollo highlands apatite grains (~ 20–1800 ppm H2O).
I was glad to see this pointed out in the space.com article,Reply
"Hayden focused primarily on the mineral apatite, which contains volatiles in its mineral structure, finding it within "ferroan anorthosites" in the sample. Ferroan anorthosites are the only known lunar rocks that formed directly from the Lunar Magma Ocean, a slushy sea of molten rock that existed on the surface of the moon 4.5 million to 4.3 million years ago. Finding this volatile-rich element in the ferroan anorthosite indicates water was present in the moon's mostly molten stages and allowed researchers to study this stage of the moon's evolution directly, the first time this had been done."
The lunar magma ocean on the Moon postulated after the giant impact with Theia raises questions in my mind about how wet the Moon could be :)
“The moon's crust might have formed from an unevenly layered "slush" of magma that once covered the entire body, a new study reports. It's the latest turn of the wheel on scientists' picture of how the moon and its features formed, a picture that's been continually changing ever since Apollo astronauts brought moon rocks back to Earth in the late 1960s and early 1970s..."
Reference paper, Formation of the Lunar Primary Crust From a Long-Lived Slushy Magma Ocean, https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL095408, 13-Jan-2022.
“Abstract Classical fractional crystallization scenarios of early lunar evolution suggest crustal formation by the flotation of light anorthite minerals from a liquid magma ocean. However, this model is challenged by the > 200 Myr age range of primitive ferroan anorthosites, their concordance with Mg-suite magmatism and by the compositional diversity observed in lunar anorthosites. Here, we propose a new model of slushy magma ocean crystallization in which crystals remain suspended in the lunar interior and crust formation only begins once a critical crystal content is reached. Thereafter crustal formation occurs by buoyant melt extraction and magmatism..."