New Lunar Regolith Analysis Challenges Meteorite-Water Theory

 Planetary scientists analyzing oxygen isotopes in lunar soil from the Apollo mission sites conclude that meteorite bombardment over 4 billion years could only have delivered a tiny fraction of Earth’s water, forcing researchers to rethink a long-held theory.

Meteorites' bombardment of Earth early in the development of the Solar System may have been a significant source of Earth's water, according to previous research.

Dr. In a new study, Tony Gargano from NASA’s Johnson Space Center and the Lunar and Planetary Institute and colleagues used a novel method for analyzing the dusty debris that covers the Moon’s surface called regolith.

They discovered that meteorite delivery since approximately 4 billion years ago could only have supplied a small portion of Earth's water, even under optimistic assumptions. 

The Moon serves as an ancient archive of the impact history the Earth-Moon system has experienced over billions of years.

Where Earth’s dynamic crust and weather erase such records, lunar samples preserve them.

However, there are challenges to the records. Traditional methods of studying regolith have relied on analyzing metal-loving elements.

These elements can get muddied by repeated impacts on the Moon, making it harder to untangle and reconstruct what the original meteoroids contained.

Triple oxygen isotopes are high-precision "fingerprints" that make use of the fact that oxygen, which is the most abundant element in rocks by mass, is unaffected by impact or other external forces.

The isotopes offer a clearer understanding of the composition of meteorites that impacted the Earth-Moon system.

According to oxygen-isotope measurements, carbon-rich meteorites that were partially vaporized upon impact with the Moon made up at least 1% by mass of the regolith. 

The researchers were able to calculate the amount of water that would have been carried within these meteorites by utilizing the known properties of such meteorites. 

One of the few places where we can still interpret a time-integrated record of what was hitting Earth's neighborhood for billions of years is the lunar regolith, according to Dr. Gargano said.

"The oxygen-isotope fingerprint enables us to extract an impactor signal from a mixture that has been repeatedly melted, vaporized, and reworked." 

The findings have implications for our understanding of water sources on Earth and the Moon.

 The model's cumulative water made up only a small portion of the water in Earth's oceans when increased by roughly twenty times to account for the significantly higher rate of impacts. 

That makes it difficult to reconcile the hypothesis that late delivery of water-rich meteorites was the dominant source of Earth’s water.

 Dr. stated, "Our results do not say meteorites delivered no water." NASA Johnson's Astromaterials Research and Exploration Science Division employs planetary scientist Justin Simon. 

“They say the Moon’s long-term record makes it very hard for late meteorite delivery to be the dominant source of Earth’s oceans.”

For the Moon, the implied delivery since about 4 billion years ago is tiny on an Earth-ocean scale but is not insignificant for the Moon.

The Moon’s accessible water inventory is concentrated in small, permanently shadowed regions at the north and south poles.

These are some of the coldest spots in the Solar System and introduce unique opportunities for scientific discovery and potential resources for lunar exploration when NASA lands astronauts on the Moon through Artemis III and beyond.

The samples analyzed for this study came from parts of the Moon near the equator on the side of the Moon facing Earth, where all six Apollo missions landed.

The rocks and dust collected more than 50 years ago continue to reveal new insights but are constrained to a small portion of the Moon.

Samples delivered through Artemis will open the door for a new generation of discoveries for decades to come.

“I’m part of the next generation of Apollo scientists — people who didn’t fly the missions, but who were trained on the samples and the questions Apollo made possible,” 

Dr.  Gargano stated “The value of the Moon is that it gives us ground truth: real, physical material we can measure in the lab and use to anchor what we infer from orbital data and telescopes.”

I can't wait to see what the Artemis samples have to say about our place in the solar system for future generations. The study appears in the Proceedings to the National Academy of Sciences.