What are John Glenn's 'fireflies' and the Mercury astronaut sightings?
“Mercury astronauts described 'fireflies,' 'snowflakes,' 'lathe shavings,' and 'particles' drifting near their spacecraft. NASA later attributed the phenomena to frozen condensation reflecting sunlight as it separated from the spacecraft body.”
Project Mercury's six crewed flights (1961–1963) produced repeated astronaut reports of unidentified luminous particles drifting alongside the capsule. The phrase 'John's fireflies' was coined by John Glenn during Mercury-Atlas 6 (February 1962). PURSUE Release 02 declassifies four follow-on Mercury audio recordings: MA-7 pilot Scott Carpenter (May 1962) describing 'white particles' moving at 'random' that 'look exactly like snowflakes'; MA-8 pilot Wally Schirra (October 1962) describing 'little white objects' he later called 'particles' and 'lathe shavings'; MA-9 pilot Gordon Cooper (May 1963) referring back to 'John's fireflies' approximately 1 hour 41 minutes into his flight; and Mercury-Redstone 4 (July 1961) recovery audio. NASA's published conclusion in PURSUE attributes the phenomenon to 'frozen condensation separating from the spacecraft body,' with the white green-hued appearance caused by 'sunlight reflecting off frozen condensation.'