Noble gases from the Earth’s mantle in the lunar basalt

Noble gases from the Earth’s mantle in the lunar basalt
/ idw / ETH Zurich press release
August 17, 2022

A violent collision of the still young earth with another planet-sized object is held responsible for the formation of the moon. A new study now provides new evidence for this theory: neon and helium have been detected in a meteorite from the moon. This is the first clear evidence that the moon has inherited noble gases from the Earth’s mantle.

Thin section of a meteorite specimen, LAP 02436, Lunar Mare Basalt with glass containing the solar noble gases.

Image: ETH Zurich / Patrizia Will [Groansicht]

The moon has always fascinated people. However, it was not until the time of Galileo Galilei that scientists began to study him properly. Over the centuries, researchers have put forward various theories about the formation of the moon. Now geological and petrological scientists from Zurich are adding another piece of the puzzle to the history of the moon’s formation.

In a new study, the team shows that the moon inherited the noble gases helium and neon from the Earth’s mantle. The new findings affect the currently favored “giant impact” theory, which scientists use to explain the formation of the moon. This theory claims that the moon was formed by a massive collision between the early Earth and another celestial body. “Our discovery means that the noble gases must also be included as a factor in the giant impact theory,” says Henner Busemann, Professor at the Institute of Geochemistry and Petrology at ETH Zurich.

For the study, Busemann’s doctoral student Patrizia Will analyzed six samples of lunar meteorites. The meteorites were collected by NASA in Antarctica and made available to the researcher for her investigations. Among other things, Will determined the content of the noble gases neon and helium in these meteorite samples. It was present in much greater abundance than expected and only in the separated glass, ruling out the solar wind as the source of the noble gases. So they had to come from inside the moon and eventually be inherited from the earth. “It is an exciting discovery that for the first time we have found non-solar wind noble gases in lunar basalt material,” said Will.

Based on their new findings, the researchers propose the process as follows: The young moon was volcanically active. Magma welled up, and quickly solidified on the surface. As a result of the rapid cooling, glass particles were formed in which the noble gases neon and helium were preserved. Further lava flows quickly covered this layer of magma and shielded it from cosmic rays, especially solar winds. This prevented chemical elements in the solar wind from being stored in the glass particles and changed their chemical fingerprint, the so-called isotope signature.

But how did the magmatic lunar material with the noble gases get to Earth? Since the moon is not protected by an atmosphere, asteroids are constantly crashing onto its surface. Such an impact was likely strong enough to eject fragments from the moon’s shielded lava layers. These rock fragments came to earth as meteorites. Many are found in the deserts of Northwest Africa or, as in this case, in Antarctica.

The researchers carried out their investigations in the inert gas laboratory at ETH Zurich. There is a modern noble gas mass spectrometer. With the instrument, the research team was able to measure glass particles less than one millimeter in size from the meteorites. It is so sensitive that it is the only instrument in the world that can detect such low concentrations of helium and neon. It was also used to detect these noble gases in Murchison meteorite grains. The grains are about seven billion years old.

Knowing where to look in NASA’s collection of about 70,000 meteorites is crucial in a project like this. “I firmly believe that there will be a race to study heavy noble gases and isotopes in this meteorite material,” says Busemann, one of the world’s leading scientists in the field of extraterrestrial noble gas geochemistry. He expects that researchers will soon look for noble gases such as xenon and krypton as well as other volatile elements such as hydrogen or halogens in the lunar meteorites.

“Although noble gases are not necessary for life, it would be interesting to know how they survived the brutal and violent formation of the Moon. This knowledge could help geochemical and geophysical scientists develop new models that more generally show how such highly volatile elements can survive the formation of planets in our solar system and beyond,” says Busemann.

The team reports on their results in a specialist article published in the journal
Science advances


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