The origin of the volatiles in the interior of the Moon is debated. The scenarios range from inheritance to a formation disc of the Moon or too late “synestial” accretion by meteorites or comets. Noble gases are excellent tracers of volatile origin.
For nearly five centuries, researchers proposed numerous hotly debated theories about how the Moon formed. Now, geochemists, cosmochemists and petrologists from ETH Zurich are shedding new light on the Moon’s origin story.
In a new study, scientists show that the Moon inherited the indigenous noble gases helium and neon from the Earth’s mantle.
The scientists analyzed six lunar meteorite samples from an Antarctic collection obtained from NASA. Meteorites are made of basaltic rock, created when magma rose from the interior of the Moon and soon cooled. After they formed, new layers of basalt continued to cover them, protecting the rock from cosmic rays and, in particular, from the solar wind.
The lunar glass particles were created during the cooling process along with other minerals found in the magma. The scientists found that the glass particles still have helium and neon chemical fingerprints (isotopic signatures) from the Moon’s interior. Their results show that the Moon inherited the native noble gases from Earth.
Cosmochemist Patrizia Will, formerly of ETH Zurich in Switzerland, now at Washington University in St. Louis, said: “Finding solar gases, for the first time, in basaltic materials on the Moon that are not related to any exposure on the lunar surface was such an exciting result.”
Asteroids constantly attack the surface of the Moon because it has no atmosphere. Presumably, the meteorites were ejected from the middle strata of the lava flow, which was similar to the great plains known as the Lunar Mother, by a high-energy impact. The rock fragments eventually reached Earth in the form of meteorites. In this case, the “cold desert” of Antarctica, where they are easier to see in the landscape, many of these meteorite samples are found in the deserts of North Africa.
Using the Tom Dooley instrument at ETH Zurich, the scientists measured submillimeter glass particles in the meteorites and ruled out the solar wind as the source of the detected gases. The helium and neon they detected were much more abundant than expected.
Professor Henner Busemann of ETH Zurich, one of the world’s leading scientists in extraterrestrial noble gas geochemistry, said: “Knowing where to look within NASA’s vast collection of around 70,000 approved meteorites represents a major step forward . I strongly believe that there will be a race to study heavy noble gases and isotopes in meteoritic materials.”
“Soon, scientists will look for noble gases like xenon and krypton, which are harder to identify. They will also look for other volatile elements like hydrogen or halogens in lunar meteorites.”
“Although these 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. This knowledge could help geochemical and geophysical scientists create new models that generally show how these more volatile elements can survive planet formation in our solar system and beyond.”
Journal reference:
- Will, P., Busemann, H., Riebe, M., Maden, C.: Indigenous noble gases in the Moon’s interior, Science Advances, 10 August 2022. DOI: 10.1126/sciadv.abl4920