Space

First A-bomb casts light on Moon's origin

First A-bomb casts light on Mo...
Trinity fireball 0.016 second after explosion
Trinity fireball 0.016 second after explosion
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Scripps Professor James Day analyzes glass formed from nuclear test explosion
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Scripps Professor James Day analyzes glass formed from nuclear test explosion
A specimen of trinitite
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A specimen of trinitite
Trinity fireball 0.016 second after explosion
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Trinity fireball 0.016 second after explosion

How did the Moon form 4.5 billion years ago, and why is it so different from the Earth? According to a team led by John Day at Scripps Institution of Oceanography at the University of California San Diego, part of the answer may be found in a mineral created by the first nuclear bomb test in 1945. By comparing samples of the atomic-age glass called "trinitite" with samples returned from the Moon by the Apollo astronauts, the Scripps team are gaining a better understanding of the chemistry of our satellite in its earliest days.

On July 16, 1945, a group of scientists, soldiers, and engineers gathered in the desert outside of Alamogordo, New Mexico, in the early dawn to witness the culmination of years of top secret work. On top of a steel tower sat a device called the "Gadget," which was the first atomic bomb ever to be scheduled for detonation. Despite the tiny amount of nuclear material available to arm the bomb, the desert test was deemed necessary because the design of the plutonium fission bomb was extremely complicated, and there were fears that it might not work – or that it would work too well.

At 5:29 am MWT, the Gadget was detonated. In a millionth of a second, the bomb and tower vanished as if suddenly dropped on the surface of the Sun. The 22-kiloton explosion was small by modern standards, but it was over twice what was anticipated. The countryside was lit up by a light many times more powerful than that of the midday Sun.

When a lead-lined Sherman tank was sent in later to take chemical samples, the driver saw that the ground was covered to a distance from blast site of 300 to 350 m (985 to 1,200 ft) with a green, glassy material. This was the first trinitite – a man made mineral that was formed when the sandy desert floor was subjected to a temperature of 8,430⁰ K (14,714⁰ F, 8157⁰ C). The heat was so intense that some samples of trinitite have a reddish tint due to absorbing the iron, lead, and copper that were part of the bomb tower before it vaporized in the nuclear fireball.

A specimen of trinitite
A specimen of trinitite

Day and his team hypothesized that the conditions that created trinitite were very similar to those that occurred when a Mars-sized object may have struck the primordial Earth and formed the Moon. Their reasoning was that by studying the volatile elements, like zinc, in samples of trinitite and comparing them to lunar samples, the Moon's formation would be less of a mystery.

For their study, the Scripps scientists collected test samples from the original Trinity site (now a national monument) at distances of 10 to 250 m (33 to 820 ft) from ground zero. They then returned to the lab and the trinitite was run through a mass spectrometer to measure the quantity and type of zinc isotopes in each sample. They found that the zinc had dried out of the trinitite, with less zinc in samples that were closer to the blast.

"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," says Day. "This has been conventional wisdom, but now we have experimental evidence to show it."

Scripps Professor James Day analyzes glass formed from nuclear test explosion
Scripps Professor James Day analyzes glass formed from nuclear test explosion

The next step was to compare the Alamogordo findings with isotope measurements of lunar rock samples brought back by the Apollo missions. In both cases, there was a lack of volatile elements and little or no water present. In other words, the same chemical processes at high temperatures that created the trinitite were present at the creation of the Moon, which supports the idea of it being formed by a giant impact billions of years ago.

"We used what was a history-changing event to scientific benefit, obtaining new and important scientific information from an event over 70 years ago that changed human history forever," says Day.

The findings are published in Science Advances.

The video below discusses the study.

Testing Moon Formation Theories

Source: Scripps Institution of Oceanography

7 comments
Bob Stuart
The Alamagordo bomb was a Uranium gun type. My mother was on a bus 200 miles away, and didn't notice it. If the yield was double the prediction, I'm surprised that Feynman didn't mention it in his book with the story of the calculating process. The Nagasaki bomb was the first Plutonium implosion.
VincentBrennan
My understanding is just the opposite. Little Boy, the bomb dropped on Hiroshima, was a long uranium powered bomb. It's shape came from the process used which was to fire a uranium wedge down a "gun barrel" into a uranium ball. Basically a very simple design. Fat Man, the Nagasaki bomb, and Gadget were plutonium and they were round. They were round due to the design that was a very complicated (compared to Little Boy) design which had a plutonium core surrounded in a round casing of high explosives that were detonated at the exact same time (this timing what was so complicated in an analog, non digital, time in history) to compress the plutonium to the point of critical mass. I am not the only one that sees it this way: https://en.wikipedia.org/wiki/Little_Boy When I was a kid I had a piece of trinitite from the bomb given to me by a man that was there!
f4ccc9a576964dcfb490f3b613abcb1b
@ Bob, You are correct about the uranium being used in a "gun barrel" type of device. They had used a segment of a Naval Battleship 16" gun for containment as they fired a slug of uranium into the mass at the other end. A friend of my father, both of who were in the "Merrill's Marauders" fighting in Burma, was Nisei and his Mother died in the first attack in Hiroshima. That man's name is "Roy" Matsumoto and he saved many Marauder's lives with his courage.
Zerozen
@Bob Stuart The Alamogordo bomb was a Implosion type, The Gadget. Prior the firstever testing, There where 2 types of design competing, code named "Fat Man"( Implosion type-Plutonium) and " Thin Man"(Gun type-Uranium) which has a problem of predetonation.
Donkey of Rodent
Taking a look at the paper, the researches appear to have overlooked some significant factors that might meaningfully affect outcomes. There doesn't appear to be any consideration of the effects of a fission detonation in close proximity with respect to changes in isotopes. At least two important aspects jump out. Neutron activation could deplete zinc and leave more galium and perhaps germanium as well as more copper and perhaps nickel. Additionally, isotopes of zinc could be the result of fission products or decay daughters thereof. . This study also seems to handwave away the vaporize zinc. Where did this go? Space? Earth? The moon? Do we find volitile vaporized dust anywhere?
JimFox
Trinity bomb was indeed plutonium implosion design. I too thought the opposite, since the first bomb produced was uranium gun-type. Refining uranium to weapon-grade took so long that the plutonium [from Hanford reactor?] 'overtook' it, making production of a plutonium device possible every 3 weeks, whereas the Uranium critical mass had taken years. Therefore it made sense to test the Fat Man design first- in case more than 2 bombs were needed.
windykites
If the Trinity bomb was a plutonium device(it was spherical,and therefore an implosion design) and successful, I wonder why they went to the trouble of making the uranium 235 device, the material of which took so much effort to extract. I have a photo of the Nagasaki core being carried by an engineer. It was tiny!