Several people contacted astronomy and weather websites to report seeing a streak of light on Wednesday night last week.
Nasa has now confirmed that the heavenly display was the result of entirely corporeal activities – the space shuttle Discovery had just dumped nearly a fortnight's worth of astronaut waste.
It is not unusual for shuttles to eject urine, but this batch was particularly large and visible because the crew had been unable to unload waste for the duration of their 10-day stay on the International Space Station.
"It would have been a large quantity because we don't do water dumps while docked to the station now," a Nasa spokeswoman told the website Space.com.
"That is a fairly new restriction over the last couple of flights in order to prevent potential contamination."
Discovery finally landed in the Mohave Desert in California on Thursday Sept 13, after poor weather forced the seven-man crew to keep circling the world for an extra day.
During its mission the shuttle delivered more than seven tonnes of food, supplies, equipment and spare parts to the $100 billion, 16-nation orbital outpost.