Scientists found an enriched uranium particle over the Aleutian Islands and don’t know where it came from. In 20 years of aerial surveys, it’s the first time researchers have detected a particle like this. It’s not naturally occurring uranium – it’s the kind that might be found in nuclear bombs or fuel.

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Dan Murphy wasn’t looking for uranium in August 2016. He wasn’t attempting to sample any radioactive material. He was looking into what particles are in the atmosphere as part of a global survey that could help people better understand air pollution and the climate for the National Oceanic and Atmospheric Administration.

During the flight from Anchorage to Hawaii, Murphy collected thousands of particles and it wasn’t until he was analyzing the samples back on the ground that he realized what he had.

“We have this mystery particle that we have no way of making that we know about,” Murphy said. “Right now it’s sort of an interesting mystery.”

The mystery particle is enriched uranium — the type of uranium associated with nuclear fuel or bombs, but Murphy says people of the Aleutians do not need to be worried about one atmospheric particle of uranium.

“It’s not going to change world politics,” Murphy said.

The particle was so small that it can’t be seen even with a small optical microscope.

What Murphy can tell is that the uranium probably came from somewhere in Asia. But even using wind trajectories and particle dispersion models, he can’t pin it on a specific country. Murphy says this discovery won’t change how he does his research.

“This was rare enough that I don’t think if I did more flights I would see another one,” Murphy said.

Murphy recently published a paper about the particle with the hope that another scientist – maybe one who knows a lot about uranium will help solve this mystery.