It was 1962 and American John Glenn was orbiting the Earth in Friendship 7, his capsule on the Mercury-Atlas 6 flight. Ground controllers were mystified at Glenn's report of fireflies outside his window, strange bright specks that clustered about his ship. The first thought was that they must be ice crystals from Friendship 7's hydrogen peroxide attitude control rockets, but Glenn was unable to correlate their appearance with the use of the rockets. Astronauts on later flights reported similar bright specks, and eventually we learned enough about the space environment to identify what they were. Spacecraft tend to accumulate clouds of debris and contamination around themselves, and even though Glenn's rockets sprayed jets of crystals away from the capsule, many of the crystals would gather in this contamination cloud, where they reflected sunlight and interacted with other gases in the cloud. Experiments on board Skylab in the 1970's using quartz-crystal microbalances confirmed and further characterized this phenomenon. The case of John Glenn's mysterious fireflies was solved.
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