Discovery changes understanding of the history of water on the Moon
New research shows that more than 4 billion years ago, the early lunar crust was enriched in water, which contradicts previously accepted assumptions.
Working with a meteorite from the Moon, graduate student Tara Hayden discovered the mineral apatite (the most common phosphate) in a sample of the early lunar crust.
«The discovery of apatite in the early crust of the Moon is quite exciting as we can finally begin to understand this unknown stage of lunar history. We found that the early crust contained more water than we expected, and its volatile stable isotopes reveal an even more complex history than we previously knew. Lunar meteorites are revealing new, fascinating pieces of the Moon's evolution and expanding our knowledge beyond the samples collected during the Apollo missions. As a new phase of lunar exploration begins, I look forward to what we will learn about the far side of the Moon», — said Hayden, currently working as a cosmochemist.
After the delivery of Apollo samples from the Moon, they were initially thought to contain little «volatile matter», leading to the well-known description of the Moon as «insanely dry».
In 2008, Alberto Saal and other researchers discovered the presence of significant amounts of water and other volatiles from the Apollo sample collection. Fifteen years of re-analysis of the samples followed, and new lunar meteorites revealed that there was much more water on the surface of the Moon.
«We know most about the history of water on the Moon from Apollo samples, but these samples are thought to represent only five percent of the Moon's entire surface. Until we have more samples from the upcoming Artemis missions, the only other surface samples we have are lunar meteorites, — Hayden said.
Hayden made the discovery while testing a rock sample for a collector as a lunar meteorite. In addition to its identification, the sample turned out to contain key information about water on the Moon.
«I was lucky that the meteorite was not only from the Moon, but, most surprisingly, had exactly the chemical composition that is important for our understanding of minerals containing water on the Moon»,— Hayden said.
This work focused primarily on the mineral apatite, which contains volatile elements in its mineral structure. Apatite has been found in all types of lunar rocks except the early crust of the Moon. The Ferroanorthusite group is known to be very old (4.5-4.3 billion years old) and is the only rock type known to have formed directly from the Lunar Magma Ocean when the Moon was almost completely molten. The discovery of apatite in this type of rock made it possible for the first time to directly study this unknown stage in the development of the Moon.
«Unraveling the history of water in the early lunar crust, approximately 4.5 billion years ago, is important for improving our understanding of the origins of water in the solar system. Ancient rock samples from the Moon in the form of lunar meteorites provide an excellent opportunity for such research», — said Mahesh Anand, Hayden's supervisor.
Hayden says the timing of the discovery was ideal as NASA's Artemis mission prepares to launch and researchers, including its scientific director, work to develop programs and goals for astronauts: «It had long been thought that the lunar surface has been dry for thousands and even millions of years ago, but perhaps there is more water on the surface of the moon than we thought, and we just need to find a way to extract it.