The Briefing Room
General Category => Science, Technology and Knowledge => Space => Topic started by: Kamaji on August 23, 2022, 08:06:36 pm
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One more clue to the Moon's origin
Date: August 10, 2022
Source: ETH Zurich
Summary: Researchers discover the first definitive proof that the Moon inherited indigenous noble gases from the Earth's mantle. The discovery represents a significant piece of the puzzle towards understanding how the Moon and, potentially, the Earth and other celestial bodies were formed.
Humankind has maintained an enduring fascination with the Moon. It was not until Galileo's time, however, that scientists really began study it. Over the course of nearly five centuries, researchers put forward numerous, much debated theories as to how the Moon was formed. Now, geochemists, cosmochemists, and petrologists at ETH Zurich shed new light on the Moon's origin story. In a study just published in the journal, Science Advances, the research team reports findings that show that the Moon inherited the indigenous noble gases of helium and neon from Earth's mantle. The discovery adds to the already strong constraints on the currently favoured "Giant Impact" theory that hypothesizes the Moon was formed by a massive collision between Earth and another celestial body.
Meteorites from the Moon to Antarctica
During her doctoral research at ETH Zurich, Patrizia Will analysed six samples of lunar meteorites from an Antarctic collection, obtained from NASA. The meteorites consist of basalt rock that formed when magma welled up from the interior of the Moon and cooled quickly. They remained covered by additional basalt layers after their formation, which protected the rock from cosmic rays and, particularly, the solar wind. The cooling process resulted in the formation of lunar glass particles amongst the other minerals found in magma. Will and the team discovered that the glass particles retain the chemical fingerprints (isotopic signatures) of the solar gases: helium and neon from the Moon's interior. Their findings strongly support that the Moon inherited noble gases indigenous to the Earth. "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," says Will.
Without the protection of an atmosphere, asteroids continually pelt the Moon's surface. It likely took a high-energy impact to eject the meteorites from the middle layers of the lava flow similar to the vast plains known as the Lunar Mare. Eventually the rock fragments made their way to Earth in the form of meteorites. Many of these meteorite samples are picked up in the deserts of North Africa or in, in this case, the "cold desert" of Antarctica where they are easier to spot in the landscape.
Grateful Dead lyrics inspire lab instrument
In the Noble Gas Laboratory at ETH Zurich resides a state-of-the-art noble gas mass spectrometer named, "Tom Dooley" -- sung about in the Grateful Dead tune by the same name. The instrument got its name, when earlier researchers, at one point, suspended the highly sensitive equipment from the ceiling of the lab to avoid interference from the vibrations of everyday life. Using the Tom Dooley instrument, the research team was able to measure sub-millimetre glass particles from the meteorites and rule out solar wind as the source of the detected gases. The helium and neon that they detected were in a much higher abundance than expected.
The Tom Dooley is so sensitive that it is, in fact, the only instrument in the world capable of detecting such minimal concentrations of helium and neon. It was used to detect these noble gases in the 7 billion years old grains in the Murchison meteorite -- the oldest known solid matter to-date.
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Source: https://www.sciencedaily.com/releases/2022/08/220810161042.htm
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Interesting. Consider, though, metals on the earth's surface, at least those not from impact structures (Sudbury?) generally have taken the form of oxides and sulfides, with the exception of banded iron formations in the mid continent (Minnesota and Canadian Shield) which are much older rocks than most of the surface. Still those represent environments of formation billions of years younger than the formation of the Moon, the oldest I have handled being a mere 2.4 Billion years old (Kenoran Fault Block, SW Ontario).
While older rocks have been found in North America, the oldest at 4.28 billion years old from the eastern side of Hudson's Bay, That's the general neighborhood for old rocks, at the center of the Craton, with a granitic gneiss from Granite Falls MN aged at 3.8 billion years old. Consider, though, that the 4.28 billion year old rocks of the Hudson's Bay formed a mere 220 million years after the moon and in geological terms, that's fairly close.
Of course, this begs the question of how long it would take a planet to recover from the sort of impact that would strip away about 1 1/4 percent of the Earth's Mass, to reconfigure back into a more or less spheroidal shape, for the axial rotation to stabilize, and the new dynamic of having another object sharing its orbit?
If the impact origin theory is correct, where was that impact? Granted, the current continents have been breaking up, moving, colliding, breaking up, and colliding yet again, in a series of orogenic episodes that have built the North American and presumably, other continents by welding their margins back to their central cores: (https://upload.wikimedia.org/wikipedia/commons/thumb/a/a7/North_america_basement_rocks.png/300px-North_america_basement_rocks.png)
All since the formation of the Moon, but at some point, there should be rocks around that were in existence when the Moon formed.
As always, more questions than answers..
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So cool.love the astronomy articles