A NASA-funded study is giving scientists insight into how “night-shining clouds” form in the upper atmosphere — and the role that growing space traffic plays in the phenomenon.

Scientists have known about these high-flying clouds since at least the late 1800s — well before the space age that launched in 1957. Newer research, however, shows that these clouds tend to form in high-altitude areas with abundant water vapor, such as what is produced after modern-day rocket launches.