Carl Sagan Shared a Shocking Space Secret

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AAs the Cold War brewed between the United States and the Soviet Union, both countries came up with some pretty outlandish ideas, but one of the most mind-boggling was the once-classified plan to detonate a nuclear bomb on the Moon before humans set foot there.

After the USSR made cosmic history by sending the world’s first artificial satellite, Sputnik, into space in 1957, the United States hoped to follow up with an unprecedented display of power. According to a 1959 report declassified in 2000, “specific positive effects would result from the nation accomplishing such a feat for the first time.”

These bizarre plans might have remained secret to this day if not for Carl Sagan, famous astronomer, science popularizer and pioneer in alien hunting. Sagan, at the time a Ph.D. student at the University of Chicago, was recruited by Dutch astronomer Gerard Kuiper, namesake of the Kuiper Belt composed of icy objects that form a massive disk beyond the orbit of Neptune. The US Air Force had tapped scientists from the Armor Research Foundation (ARF) laboratory, based in Chicago, to lead what became known as Project A119.

“The main purpose of the proposed detonation was a public relations exercise and a show of one-upmanship. The Air Force wanted a mushroom cloud so large that it would be visible on Earth,” said Leonard Reiffel, a physicist on the A119 project. The observer in 2000. “The United States was lagging behind in the space race. »

Read more: »How the Cold War Created Astrobiology»

Reiffel warned A119 project planners of “enormous cost to science” by “destroying a pristine lunar environment.” In fact, the bomb crater could have disfigured the face of the “man in the moon.” But the daring feat was technically feasible at the time, he noted, using an intercontinental ballistic nuclear missile, equipped with a warhead roughly the size of the atomic bomb dropped on Hiroshima, or larger.

Sagan was on a mission to determine whether researchers could “gather scientifically useful information by detonating nuclear weapons on the Moon,” and he also explored the potential effects of radioactive fallout on the Moon, according to the 1999 biography: Carl Sagan: a life by Keay Davidson.

Ultimately, the US Air Force terminated the A119 project. The exact reasons remain unclear, but some theories suggest that the government wanted to avoid any potential harm to Earthlings or feared that the Moon might be contaminated with radioactive substances.

But stories of the failed plan will live on thanks to Sagan, who shared details of the project in 1959 when applying for a graduate fellowship at the University of California, Berkeley — an error Davidson noticed while researching the book. Sagan’s friends ‘believe he would never have deliberately revealed classified information,’ says The observer. Later in his career, however, Sagan spoke of the dire risks of nuclear war: it could “destroy world civilization and, perhaps…could end a few million years old experiment, a human experiment, on planet Earth,” he said in a 1987 speech.

Carl Sagan is famous for unlocking the cosmos and making the mysteries of the universe accessible to ordinary people through clear and compelling storytelling. Among these astronomical achievements, it seems, is the inadvertent revelation of the harrowing story of a Cold War show of force that could have marred lunar exploration for generations to come.

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Main image: Internet Archive Book Images / Wikimedia Commons

• Molly Glick

  Published on November 10, 2025

  Molly Glick is the newsletter editor of Nautilus.