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What the first nuclear explosion tells us about the Moon’s formation

During the first nuclear explosion on July 16, 1945, at the Trinity test site in New Mexico, USA (the "test" that later led to the atomic explosions at Hiroshima and Nagasaki), the very high temperatures generated "vitrified" some of the surrounding sand.

What the first nuclear explosion tells us about the Moon’s formation

Bikini Atoll

Publication date: 08/02/2017

Press, Research

Related themes : Origins

These “anthropogenic” glasses, known as Trinitites, were the subject of a study by an IPGP team comprising James Day and Frédéric Moynier, published on February 8 in the journal Science Advances. The authors of this study measured the differences in chemical composition between the initial “arkosic” sand and the silicate glasses obtained to study the consequences of the explosion, whose pressure and temperature conditions (equivalent to 20,000 tonnes of TNT) are close to those that prevailed on the surface of planets during their formation.

Previous studies have shown that the abundances of volatile elements and compounds acquired during the early stages of the solar system’s evolution vary widely from planet to planet. The Moon, for example, is largely depleted in volatile elements compared to the Earth, probably as a result of its formation during a giant impact on the Earth’s surface. But the extreme pressure and temperature conditions prevailing during giant impacts make it difficult to experiment and reproduce in the laboratory results measured on natural samples.

The study of the chemical composition, and more specifically the volatile elements, of samples of these “trinitites” taken between 10 and 200 m from the site of the explosion, shows that the glasses formed closest to the detonation are depleted in volatile elements, such as Zn, and enriched in heavy isotopes, compared with samples formed further away.

These results show unequivocally that high-temperature evaporation processes, similar to those that occurred during the formation of planets and the Moon, lead to the loss of volatile elements and enrichment in heavy isotopes in the residual material.

Furthermore, the degree of volatile depletion in the silicate glasses obtained, as estimated during this study at the Trinity site, is similar to the volatile depletion rates in lunar samples, and therefore provides a better understanding of how volatiles were redistributed during the formation of the Moon.

Finally, it is important to note that this study obtained new and scientifically important results from samples produced during a major historical event that took place 70 years ago and changed mankind forever.

Réf : James M. D. Day, Frédéric Moynier, Alex P. Meshik, Olga V. Pradivtseva, Donald R. Petit, Evaporative fractionation of zinc during the first nuclear detonation, Sci. Adv. 2017

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