Mercury Atlas 9 Audio Excerpt, May 15, 1963
A short audio clip from Gordon Cooper's solo orbit aboard Faith 7 captures the moment he spots the same mysterious luminous particles John Glenn had reported a year earlier — drifting alongside the capsule and glowing white-green against the black of space. NASA's working explanation is frozen condensation shedding off the spacecraft hull, lit by direct sunlight. It's a useful case study in how an genuinely puzzling observation gets investigated and resolved — and a reminder that even experienced astronauts needed time to understand what they were seeing outside their windows.
Approximately one hour and 41 minutes into the final and longest flight of Project Mercury, Mercury-Atlas 9 mission (MA-9) Faith 7 Pilot L. Gordon Cooper Jr. notes that he sees “John’s fireflies,” referring to John Glenn’s term from the Mercury-Atlas 6 mission. NASA later determined that the “fireflies” are attributable to frozen condensation separating from the spacecraft body. The white, green-hued appearance of this phenomenon results from sunlight reflecting off frozen condensation.