Gordon Cooper Spotted Greenish “Fireflies” Near His Spacecraft

Midway through a spaceflight, Gordon Cooper spotted white specks with a greenish tint. He called them “John’s fireflies,” a sighting captured in a recording from his flight.

The specks looked like living things floating in space. But the explanation was simple: they were water droplets that had frozen and broken away from the spacecraft. Sunlight reflecting off them made them appear white with a greenish tint.

A Nickname Passed From Pilot to Pilot

Cooper piloted Faith 7, the final and longest flight in Project Mercury, the early American space program. In the recording, he said he could see “John’s fireflies.”

The nickname didn’t originate with Cooper. He was referring to a name John Glenn had used during an earlier spaceflight. When glowing specks appeared in front of Cooper during his flight, he used the same nickname.

What Made Them Greenish?

NASA later determined that the specks were frozen water droplets that had separated from the spacecraft. Sunlight reflecting off the droplets gave them their white, greenish appearance.

They may have looked like fireflies, but they were made of something simple and familiar: frozen water. The droplets were near the spacecraft, and sunlight made them visible as specks in space. That’s why Cooper’s nickname sounds so evocative, even after the source of the lights became clear.

What Remains Unknown

The source does not explain why the droplets separated from the spacecraft. Nor does it say how many specks Cooper saw or how long they remained visible. NASA determined only what they were and how they came to look that way.

Frozen water droplets, sunlight, and a nickname passed between two pilots. That’s what Cooper’s fireflies looked like in space.