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The early lunar crust had a lot of water at the beginning of our solar system’s formation, more than four billion years ago. The new research from a Western University postdoctoral fellow on this topic was published in Nature Astronomy on Jan. 15.
Fellow Tara Hayden, while a Ph.D. student at the Open University, scrutinized a meteorite she identified as having come from the Moon. She found a mineral known as apatite, a phosphate, in the meteorite and determined it came from the early lunar crust.
The study adds on to past scrutinies of Apollo samples, which were found to have contained water in 2008. Previous generations of instruments did not have the sensitivity to look for traces of water in the rocks, which were collected between 1969 and 1972. Alberto Saal’s team was the first to find water and other volatiles in glass beads from Apollo samples, sparking continuing re-analysis of these samples (and more discoveries of water) in several studies in the past 15 years.
SpaceQ spoke with Hayden to learn more about why this discovery is significant, and how this may help for the forthcoming Artemis missions. Artemis 3 is now expected to land astronauts on the Moon no earlier than 2026. The timeline will depend on how ready the SpaceX Starship lander, the private spacesuits from Axiom Space, and other systems are. Additionally, a human mission called Artemis 2 (carrying Jeremy Hansen from the Canadian Space Agency, along with three NASA astronauts) was recently delayed nine months to launch no earlier than September 2025; that may also play into how soon Artemis 3 lands on the surface.
SpaceQ: The meteorite you studied is from the lunar crust. Do you know about what part of the Moon it came from: near side, far side, a particular region?
Hayden: Meteorite scientists are working towards being able to pinpoint where meteorites may have originated from the Moon’s surface. However, we still have some way to go to narrow this down. We do know that this meteorite contains various samples of the lunar “highlands” rocks, which represent the various rocks making up the Moon’s crust, as well as rocks formed by melting during impact events. This indicates it could have come from the “highlands” regions — the light/bright parts of the Moon’s surface.
SpaceQ: Compared to the Apollo samples that get as close to the crust as they could have, can you describe the difference in age and composition of the meteorite you studied?
Hayden: There is a large spread of Apollo ferroan anorthosite, or FAN, ages. Most fall between ages of 4.3 billion and 4.5 billion years old. This sample is among the oldest of the FAN rocks from Apollo, as it has an age of 4.47 billion to 4.54 billion years old, with some Apollo 16 FAN samples giving ages of 4.51 to 4.56 billion years old.
Other non-FAN crustal rocks have ages of 4.54 billion to 4.55 billion years old. These rocks were likely formed deeper within the Moon, which indicates that the Moon was cooling and crystallizing – rather than remaining molten – by 4.55 billion years ago.
This meteorite, called Arabian Peninsula 007, is rich in iron and calcium. That’s like much of the early lunar crust — the enrichment in iron being why we give it the name “ferroan” — though this meteorite is moderately richer in magnesium than many FAN samples. This could indicate it is more primitive, as earlier formed crystals tend to be richer in magnesium.
SpaceQ: What does apatite show us about the conditions of the lunar crust during its formation, and how does that point to water?
Hayden: The presence of apatite in the lunar crust allows us direct insight into the nature of volatile elements – elements with low boiling points like hydrogen – at the time when the Moon was entirely molten. This period was called the Lunar Magma Ocean or LMO, as these rocks directly crystallized from the molten magma. This is a poorly understood period in lunar history because of the absence of minerals or materials such as apatite that have water and other volatiles in their mineral structure. From this, we can look at the Apollo rocks and lunar meteorites and their water or volatile natures, and create a clear model of how water evolved on the Moon.
SpaceQ: Could we possibly get more ground truth on the crust/apatite at the south pole of the Moon, the approximate landing zone of the Artemis missions?
Hayden: The return of samples from the south pole on the Moon will be better ground truth of the crust and apatite. The lunar far side – including the south pole – has a very high albedo, which is typical for the primary lunar crust. Comparing near side and far side samples will be crucial to understanding how the Moon’s crust evolved — whether it was consistent across its formation, or whether the far side crust formed differently. I am incredibly excited for Artemis!
SpaceQ: What are your next steps for the research. For example, are there other samples you would like to look at from Apollo or from meteorites or are there similar indicators of water you’ll be looking for?
Hayden: I would really love to look at more samples of the lunar crust from Apollo and meteorites and try to find more apatite. The Apollo 16 samples are going to be a priority to examine, as these widely sample FANs. Lunar meteorites, however, can come from anywhere on the Moon’s surface. Thus, studying these for apatite will be key to understanding the Moon’s crust as a whole prior to sample return in the Artemis and other upcoming lunar missions.
SpaceQ: Besides the water takeaway, what do you feel is the most important thing for readers to know about the discovery?
Hayden: This discovery indicates that the Moon had crystallized before 4.5 billion years ago, likely within 60 million years of calcium-aluminum-rich inclusions (CAIs) which are small metallic droplets thought to be the oldest solid material in the Solar System
SpaceQ: Anything else you want to add?
Hayden: The next decade of lunar science is going to be incredibly exciting to see unfold, and I really look forward to more discoveries that help us piece together the Moon’s history.
This interview has been edited and condensed for clarity.
