An additional clue to the Moon’s origin.
The Moon has always been a topic of interest for humans. But it wasn’t until Galileo’s time that researchers started to study it seriously. Throughout the course of nearly five hundred years, researchers have proposed a variety of, highly contested ideas as to how the Moon was formed. Geochemists, cosmochemists, and petrologists from ETH Zurich have now shed new light on the Moon’s origin story.
The research team’s findings, which have recently been published in the journal Science Advances, demonstrate that the Moon acquired the indigenous noble gases helium and neon from the Earth’s mantle. The finding strengthens the already tight constraints on the widely accepted “Giant Impact” theory, which theorizes that Earth and another celestial body collided violently to form the Moon.
Meteorites from the Moon to Antarctica
Patrizia Will examined six samples of lunar meteorites from an Antarctic collection that NASA provided for her doctoral work at ETH Zurich. The meteorites are made of basalt rock, which was created when magma welled up from the Moon’s interior and quickly cooled. After they formed, additional layers of basalt proceeded to cover them, shielding the rock from cosmic rays and, in particular, the solar wind. The cooling process resulted in the creation of lunar glass particles amongst the other minerals found in magma.
Will and the team found that the glass particles still had helium and neon chemical fingerprints (isotopic signatures) from the Moon’s interior. Their results provide compelling evidence that the Moon inherited the 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 constantly pelted 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 were 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 previous 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-millimeter 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 on Earth 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.
Searching for the origins of life
Knowing where to look inside NASA’s vast collection of some 70,000 approved meteorites represents a major step forward. “I am strongly convinced that there will be a race to study heavy noble gases and isotopes in meteoritic materials,” states ETH Zurich Professor Henner Busemann, one of the world’s leading scientists in the field of extra-terrestrial noble gas geochemistry. He anticipates that soon researchers will be looking for noble gases such as xenon and krypton which are more challenging to identify. They will also be searching for other volatile elements such as hydrogen or halogens in the lunar meteorites.
Busemann comments, “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. 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.”
Reference: “Indigenous noble gases in the Moon’s interior” by Patrizia Will, Henner Busemann, My E. I. Riebe and Colin Maden, 10 August 2022, Science Advances.