Lunar meteorite provides glimpse into Moon’s ancient past
A new study published in Nature Astronomy reveals that the Moon’s crust contained far more water early in its history than scientists had previously realized. The findings come from an analysis of a lunar meteorite found in Africa’s Sahara Desert in 2020. At 2.61 billion years old, the meteorite contains the oldest crust fragment ever recovered from the Moon, providing unique insights into our satellite’s ancient past.
“This meteorite represents a really exciting discovery – it’s unlike anything else ever studied in the lab,” said lead author Dr. Katherine Burgess, a geochemist at Western University in Canada. “It suggests the Moon’s water history is more complex than suspected, with the ancient lunar crust able to store water early on before later being depleted.”
The results challenge the prevalent theory that the bulk of the Moon formed from the high-speed collision of a Mars-sized planet with the proto-Earth about 4.5 billion years ago. In that model, intense heating during the formation event was believed to have boiled off any water or volatiles in the Moon’s crust.
However, trace amounts of water were detected on parts of the Moon’s surface in orbital measurements over the past 15 years. This led to speculation that water was delivered to the Moon by water-rich asteroids or comets sometime after its formation.
Rare sample provides window into Moon’s beginnings
The meteorite analyzed by Dr. Burgess and her international team likely originated from the outskirts of the Moon’s South Pole Aitken Basin, one of the largest known impact craters in the entire solar system. Formed about 4 billion years ago, the 1,550 mile-wide basin is thought to have excavated material from deep within the Moon’s mantle.
“It’s incredibly difficult to recover ancient lunar samples,” explained Dr. Burgess. “Only about 30 Moon meteorites have ever been discovered on Earth. Of those, only a handful contain crustal components with most consisting of volcanic basalts from relatively younger surfaces.”
The researchers used advanced nano-scale analytical techniques to determine the meteorite’s geochemistry and age. They found it was made up of fragments of anorthosite, a characteristic rock type that forms plagioclase feldspar – a mineral commonly found in the crusts of primordial planets. Through Uranium-Lead isotopic dating methods, they showed the anorthosite crystallized 4.1 to 4.3 billion years ago – making it nearly as old as the Moon itself at around 4.5 billion years old.
“It’s an astonishing find – I never expected to see lunar crust that dates back nearly to the Moon’s very beginnings,” remarked geologist Mahesh Anand from the Open University in the U.K., a co-author of the paper. “It tells us the Moon’s water history is more dynamic than believed with the ancient crust able to store water very early on before it was later depleted through volcanism and meteoroid impacts.”
Lunar water originated on Moon itself, not just delivered later
One of the study’s most intriguing findings relates to the water detected within mineral structures in the ancient crust fragment. Using spectral analysis combined with thermodynamic water modeling, the researchers showed the sample contains up to 413 parts per million water trapped within apatite minerals. This water signature likely represents indigenous water from the Moon inherited directly from the lunar magma ocean.
“The abundance of water we measured implies the lunar magma ocean contained significant water which was later incorporated into the primordial crust as it crystalized,” explained lead author Dr. Burgess. “These findings negate assumptions that all the Moon’s water was delivered later by objects like meteorites or comets.”
The results have important implications for understanding the origins of water ice detected in permanently shadowed regions around the Moon’s South Pole. If the ancient crust contained significant water, it’s feasible some of this water inventory could have migrated from crustal rocks into polar cold traps over geological time.
“I think we’re finally starting to unravel the Moon’s water mystery,” concluded Dr. Anand at a press briefing yesterday. “This study revolutionizes our picture of the infant Moon as a wet body, with a crust containing indigenous water present from the very start of its formation.”
Future lunar exploration to target ancient crust sites
The tantalizing clues about the Moon’s early water history revealed by the Sahara Desert meteorite will help guide future lunar exploration efforts. Several space agencies have upcoming Moon missions slated over the next decade aiming to learn more about lunar water reserves.
NASA’s VIPER rover will launch in 2028 to rove the Moon’s South Pole searching for water ice. And the agency’s Lunar Trailblazer satellite – planned to launch in 2025 – will map water ice deposits from lunar orbit. The knowledge gained about how water originated and evolved on the Moon will aid identifying the best landing sites for eventual astronaut returns to the surface this decade under the Artemis program.
“These findings will re-shape concepts for future lunar habitation,” said former NASA astronaut Dr. Tom Jones, now a senior research scientist at the Florida Institute for Human and Machine Cognition. “Understanding how water is stored locally across the lunar terrain could make it easier for long duration astronaut exploration at the Moon’s poles. In-situ resource utilization from mining water ice reservoirs will be key for sustained lunar operations.”
In addition to space agencies, the new results have sparked excitement from the growing commercial lunar industry. Over a dozen companies including ispace, Masten Space Systems, and Astrobotic have signed up for delivering science payloads and technology demonstrations to the Moon’s surface in the coming years. Several firms have proposed concepts for extracting water ice deposits as an invaluable resource to produce rocket fuel, drinking water, and breathable oxygen on site.
The Canadian Space Agency (CSA) also announced today that upcoming lunar rover missions will target more ancient crust sites to recover additional samples for laboratory analysis back on Earth. The study authors hope more meteorites derived from ancient lunar crust components – perhaps excavated by impacts – will be identified on Earth to help uncover more secrets from the Moon’s beginnings hidden within the sands of time.
Key takeaways
- Ancient 2.61 billion year old lunar meteorite contains the oldest bit of Moon crust ever discovered
- Mineral analysis reveals sample originated from outskirts of Moon’s South Pole Aitken Basin impact site
- Evidence found for indigenous water within lunar crust dating back 4.1 to 4.3 billion years
- Challenges theories that all Moon water was delivered later by comets or asteroids
- Future lunar exploration aims to study ancient crust terrain to learn more about origins of water ice at the poles
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