Using fragments of radioactive glass picked up from the site of the first nuclear bomb explosion in the United States, scientists are trying to explain the mystery behind the formation of the moon and the properties of lunar rocks.
The study by researchers from the Scripps Institution of Oceanography at the University of California, San Diego used materials from the Trinity test site in New Mexico to show that the explosion could be similar to a collision between proto-Earth and a Mars-sized object 4.5 billion years ago.
The current theory on moon formation is that a Mars-sized object called Theia bombarded the Earth and the ejected mass converged to form the moon.
The impact would have produced massive amounts of extreme heat that drove volatile compounds out of the space rocks that formed the moon. The scientists set out to prove how moon formation could be caused by high-temperature processes by analyzing the nuclear test site residue, which was formed from the same conditions as the planetary collision.
Radioactive Glass Creation
In the extreme heat of the blast on July 16, 1945, the top layer of the sandy soil melted into a green silicate glass. The radioactive glass, which was given the name trinitite, was spread across a radius of 1,150 feet from the detonation point.
For the study, James Day, director of the Scripps Geochemistry Isotope Laboratory, and team studied trinitite samples from various locations and depths ranging from within an average of 30 feet to 800 feet within ground zero.
Day and colleagues found that trinitites from the nuclear test site were short on volatile compounds such as zinc and water. The team chose to analyze zinc isotopes because zinc boils off in extreme heat, such as that generated by the supposed collision that formed the moon.
Based on the analysis, the trinitite samples obtained nearer to ground zero carried less zinc than samples from farther away. Also, the zinc that was left only had heavy isotopes, which do not normally evaporate. The deprivation of volatiles from the samples, especially in trinitites close to the site of the explosion, was the result of vaporization under high temperature, the researchers said.
"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 leftover materials from the event," said Day. He said the theory has now been backed up by experimental evidence.
Their findings led the researchers to believe that the mighty collision must have been a high-temperature event and that evaporated most volatiles, like what happened with the trinitite samples in the nuclear test site.
Day said the new study has given them the confidence that they're going in the right direction in terms of interpreting the data on the lunar rock samples brought home by the Apollo astronauts. The lunar samples also have the same volatile-loss signatures as trinitite.
The findings were published in Science Advances on Feb. 8.