Radioactive Trinitite Glass at World’s First Nuclear Test Site Helps Scientists Test Moon-formation Theories

The world’s first nuclear bomb was detonated in 1945 at a test site in the New Mexico desert, which is far away from San Diego. However, a scientist from San Diego is now collecting samples of radioactive glass trinitite from that site to test the validity of a popular moon-formation theory.

Trinitite or atomsite is a light green glass composed of sand. The 1945 Trinity nuclear test produced extreme high temperatures, which transformed sand near the site into trinitite. Scientists collected samples of this glass from the New Mexico site and measured the concentrations of volatile elements like zinc in the glass fragments. They found that glass closest to ground zero featured less zinc, and the zinc that remained was richer in heavier isotopes.

One of the many moon-formation theories argues that moon was formed from molten debris ejected when a large planetary object hit the Earth. Scientists believe after such a collision, volatile elements in glassy debris would have been vaporized, in the same way as the nuclear explosion robbed trinitite of its zinc.

Scientists also compared trinitite samples and lunar rocks and found depleted volatile elements and little to no water in both.

“Volatile element and compound abundances vary widely in planets and were set during the earliest stages of solar system evolution. Experiments or natural analogs approximating these early conditions are limited. Using silicate glass formed from arkosic sands during the first nuclear detonation at the Trinity test site, New Mexico, we show that the isotopes of zinc were fractionated during evaporation,” the author of the study writes in the paper.

“The green silicate glasses, termed “trinitite,” show +0.5 ± 0.1‰/atomic mass unit isotopic fractionation from ~200 m to within 10 m of ground zero of the detonation, corresponding to an α fractionation factor between 0.999 and 0.9995. These results confirm that Zn isotopic fractionation occurs through evaporation processes at high temperatures. Evidence for similar fractionations in lunar samples consequently implies a volatile-depleted bulk Moon, with evaporation occurring during a giant impact or in a magma ocean.”

“The results show that evaporation at high temperatures, similar to those at the beginning of planet formation, leads to the loss of volatile elements and to enrichment in heavy isotopes in the left over materials from the event,” James Day, a geoscientist at the Scripps Institution of Oceanography at the University of California San Diego, said in a news release.

“This has been conventional wisdom, but now we have experimental evidence to show it.”

The detailed findings of the study have been published in journal Science Advances.