A lunar sample brought to the land by the astronauts of Apollo 14 seems to include the first potential evidence of a terrestrial meteorite that reached our satellite.
The investigation on this possible relic of Hadeana Earth is published in the magazine 'Earth and Planetary Science Letters'.
An international team of scientists associated with the CLSE (Center for Lunar Science and Exploration), part of NASA's Solar System Exploration Research Virtual Institute, found evidence that the rock was launched from Earth by a large asteroid or impacting comet.
This impact discarded the material through the primitive atmosphere of the Earth, in space, where it collided with the surface of the Moon (which was three times closer to the Earth than now) about 4,000 million years ago. The rock was subsequently mixed with other lunar surface materials in a sample.
The team developed techniques to locate impact fragments in the lunar regolith, which led to the CLSE principal investigator, David A. Kring, scientist of the USRA (Universities Space Research Association) at the Lunar and Planetary Institute (LPI) to challenge them to locate this piece of Earth on the Moon.
Directed by the research scientist Jeremy Bellucci and Professor Alexander Nemchin, members of the team working at the Swedish Museum of Natural History and Curtin University in Australia accepted the challenge.
The result of his research is a fragment of 2 grams of rock composed of quartz, feldspar and zircon, all of them commonly found on Earth and highly unusual on the Moon. The chemical analysis of the rock fragment shows that it crystallized in an oxidized system of terrestrial type, at terrestrial temperatures, instead of in the conditions of reducing temperature and higher characteristics of the Moon.
"An extraordinary find"
"It is an extraordinary findor that it helps to paint a better image of the primitive Earth and the bombardment that modified our planet during the dawn of life, "Kring said in a statement.
It is possible that the sample is not of terrestrial origin, but that it crystallizes in the Moon, nevertheless, that would require conditions never before inferred from lunar samples. It would require that the sample be formed at tremendous depths, in the lunar mantle, where very different rock compositions are anticipated. Therefore, the simplest interpretation is that the sample came from Earth.
Team analysis provides additional details about the sample history. The rock crystallized about 20 kilometers below the surface of the Earth 4,000-4,100 million years ago. It was then excavated by one or more high-impact events and launched into the cislunar space.
Previous work done by the team showed that the impacting asteroids at that time were producing craters thousands of kilometers in diameter on Earth, large enough to bring material from those depths to the surface. Once the sample reached the lunar surface, it was affected by several other impact events, one of which partially melted 3,900 million years ago, and which probably buried it below the surface.
The sample is, therefore, a relic of an intense period of bombardment that shaped the Solar System during the first billion years. After that period, the Moon was affected by smaller and less frequent impact events. The final impact event that affected this sample occurred approximately 26 million years ago, when a striking asteroid struck the Moon, producing the small Cone crater 340 meters in diameter and digging the sample back into the lunar surface where the astronauts collected it. almost 48 years ago
Kring suspects that the conclusion of a terrestrial origin for the rock fragment will be controversial. Although Hadean Earth is a reasonable source for the sample, a first finding of this kind can be a challenge to digest by the geological community. He points out that samples from Hadeana Earth dotted the lunar surface; other samples will probably be found with an additional study.