The research team’s findings, recently published in Science Advances, demonstrate that the Moon acquires native noble gases — helium and neon — from Earth’s mantle. The discovery reinforces strict constraints on the already widely accepted theory of “giant impact”, which holds that the Earth and another celestial body collided violently to form the Moon.
Meteorites from the Moon to Antarctica
Patrizia Will examines a six-month-long meteorite sample from the South Pole collected by NASA for her doctoral work at ETH Zurich. These meteorites are made of basalt, which is created when magma pours out of the moon’s interior and cools rapidly. After they formed, additional layers of basalt began to coat them and shield the rocks from cosmic rays, especially the solar wind. The cooling process led to the creation of lunar glass grains among other minerals found in magma.
Will and the team found that the glass particles still had chemical fingerprints (isotopic signatures) of helium and neon from the Moon’s interior. Their results provide convincing evidence that the Moon inherited Earth’s native gases. “For the first time, solar gases have been found in lunar basalt material that are not associated with any exposure to the lunar surface, which is an exciting result,” Will said.
Without the protection of the atmosphere, asteroids keep smashing into the lunar surface. It is likely that a high-energy impact would be required to eject the meteorite from the middle layer of the lava flow, which resembles the vast plains known as lunar seas. Eventually, these rock fragments entered Earth in the form of meteorites. Many of these meteorite samples were picked up in the deserts of North Africa, or in this case, the “cold deserts” of Antarctica, where they are easier to spot.
In the Noble Gas Laboratory at ETH Zurich there is a state-of-the-art noble gas mass spectrometer called Tom Dooley – sung in the Grateful Dead song of the same name. The instrument takes its name from previous researchers who at one point hung highly sensitive equipment from the ceiling of their labs to avoid the vibrations of everyday life.
Using the Tom Dooley instrument, the team was able to measure submillimeter-scale glass particles from the meteorite and ruled out the solar wind as the source of the detected gas. They detected much higher abundances of helium and neon than expected.
Tom Dooley is so sensitive, in fact, that it is the only instrument on Earth that can detect such lowest concentrations of helium and neon. It was used to detect these noble gases in the 7-billion-year-old grains of the Murchison meteorite — the oldest known solid material to date.
Knowing what to look for in NASA’s vast collection of about 70,000 approved meteorites represents a big step forward. Henner Busemann, a professor at ETH Zurich and one of the world’s leading scientists in the field of extraterrestrial noble gas geochemistry, said: “I firmly believe that there will be a race to study heavy noble gases and isotopes in meteorite materials.” He expects that soon The researchers will look for more difficult-to-identify noble gases such as xenon and krypton. They will also look for other volatile elements such as hydrogen or halogens in lunar meteorites.
Busemann commented: “While these gases are not necessary for life, it would be very interesting to understand how some of these noble gases survived the brutal and violent formation of the Moon. Such knowledge may help Scientists in geochemistry and geophysics create new models that show more generally how this most volatile element survived the formation of planets in our solar system and elsewhere.”