Lunar Meteorites Help Explain Moon’s Formation

Lunar meteorites are very rare rocks that scientists sometimes discover in Antarctica or deserts. Find out how a new study of the trace gases they contain has shed light on the origins of the moon and the Earth.

Ever since Galileo used one of the first telescopes to see the craters on the moon, scientists have sought to understand how we came by our huge natural satellite.

Growing up during the Space Race, I remember television documentaries explaining that the moon formed from a big chunk of the Earth. Back then, scientists speculated that this might be the reason the Pacific Ocean is so wide and deep.

That was before the Apollo astronauts brought home samples of the lunar surface. Studying those samples has led most scientists to further propose that the moon formed from a spectacular collision involving the Earth and another planet. They call this planet Theia.

One Hundred Million Times More Powerful than Dinosaur Collision

The collision with Theia would have been 100 million times more powerful than the impact that wiped out the dinosaurs. An explosion like that would vaporize a large chunk of the Earth’s crust.

Then, over time, gravity must have pulled the vaporized particulate together. The result, according to the most accepted hypothesis, was the largest moon in our solar system.

Not everyone agrees that the moon formed from a single, giant impact. There’s another school of thought in which a shower of smaller debris caused the moon’s formation.

Other Researchers Say Earth and Moon Formed Together

Other researchers have suggested that the Earth and the moon formed together out of the sun’s debris at around the same time. Some other planets and their moons did that.

Even so, this wouldn’t explain why the Earth and the Moon have very different densities. As we know from watching the astonauts hopping around, the moon has much less gravity than Earth.

Another explanation is that the moon formed on its own and then the Earth captured it. That’s what happened with the two martian moons, Phobos and Deimos. However, the materials that make up the Earth and the moon are uncannily similar, which probably rules out that idea.

Giant Impact Hypothesis STill Not a Full Explanation

Most planetary scientists have come to accept that the simplest explanation that covers all the facts is the giant impact hypothesis. Yet, this hypothesis doesn’t fully explain why the compositions of the Earth and the Moon are so alike.

Last week, the journal Science Advances published a new study that offered some new insights into the lunar formation mystery. Its authors conclude that the moon acquired helium and neon from the Earth’s mantle.

Helium and neon are both noble gases. As most of us learned in high school, noble gases don’t form compounds with any other elements. This has implications for the giant impact hypothesis.

Six Samples of Lunar Meteorites from NASA

The new study began when Patrizia Will was working toward her doctorate at ETH Zurich, the Swiss Federal Institute of Technology. She obtained six samples of meteorites from NASA that researchers found in Antarctica.

These meteorites came from the moon. Apparently, they’re made of rock that formed when an asteroid slammed into our natural satellite.

This impact seems to have ejected magma from deep inside the moon onto the lunar surface. The molten magma would have quickly cooled into basalt rock.

Impacts Launched Meteorites Into Space – Landed in Antarctica

Millions of years later, smaller objects would have crashed into this basalt rock. These later impacts would then launch meteorites into space toward Earth. The ones that land in Antactica are the easiest to find because of the open, snow-covered landscape.

During the basalt’s cooling process after the eruption, glass particles formed within it. When Ms Will and her colleagues analyzed that glass, they discovered chemical traces of helium and neon.

Although they don’t combine with other elements, the number of neutrons inside noble gas atoms still varies. Atoms that are the same element but with different neutron numbers are called isotopes.

Noble Gas Mass Spectrometer Nicknamed “Tom Dooley”

ETH Zurich has a Noble Gas Laboratory. One of the sophisticated instruments in that lab is called a noble gas mass spectrometer.

Its nickname is “Tom Dooley,” after the title of an American folk song recorded by the Grateful Dead among many others. The lyrics say, “Hang down your head, Tom Dooley.”

This world  class instrument received its cool nickname because it hangs its head from the lab’s ceiling. This stops vibrations from routine lab activities from interfering with its measurements.

Instrument Detected Isotopes that Come from Sun

When Tom Dooley examined the helium and neon from the glass particles, it detected isotopes that normally come from the sun. Since the Earth formed along with the sun, the best explanation is that the moon’s interior somehow inherited these noble gases from Earth.

For Ms Will, “Finding solar gases, for the first time, in basaltic materials from the Moon that are unrelated to any exposure on the lunar surface was such an exciting result.”

ETH Zurich professor Henner Busemann is one of the foremost authorities on noble gases from outer space. He’s also a co-author of the study. 

“There Will Be a Race to Study Heavy Noble Gases”

“I am strongly convinced that there will be a race to study heavy noble gases and isotopes in meteoritic materials,” Professor Busemann said. “While such gases are not necessary for life, it would be interesting to know how some of these noble gases survived the brutal and violent formation of the moon.”

NASA has collected more than 70,000 meteorites over the years. This new study suggests a new way to decide which lunar meteorites are worth studying in more depth.

Since there are other, heavier noble gases, like xenon and krypton, it also implies that scientists might make further discoveries by looking for lunar meteorites containing these other elements. For that matter, they could even try searching for volatile elements like hydrogen or halogen in some of the meteorites.

Most Obvious Reminder There Are Worlds Beyond Our Own

Glancing up at the moon fills most of us with a sense of wonder. It’s the most obvious reminder that there are worlds beyond our own.

Also, since the Earth and the moon are so closely interrelated, understanding the moon is vital to gaining knowledge about our own world and our place within it.

Professor Busemann concluded by saying, “Such knowledge might help scientists in geochemistry and geophysics to create new models that show more generally how such most volatile elements can survive planet formation, in our solar system and beyond.”

We always have more to learn if we dare to learn.

Learn more:
One more clue to the Moon’s origin
Indigenous noble gases in the moon’s interior
Planetary Formation in the News
Moons May Guide Us to Life on Other Planets
Water Discoveries May Unlock Life’s Mysteries

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