Mystery Explained: Glow in Night Sky Was Astronaut Urine

The beautiful trail in the sky looked like a mysterious celestial event. In reality, it was urine.

Some skygazers were treated to the unexpected view of a bright sparkling glow Wednesday night, created when astronauts aboard the space shuttle Discovery dumped the waste out into space.

The water dump was a scheduled task for STS-128 pilot Kevin Ford, who poured out urine and waste water stored aboard the shuttle in preparation for a landing attempt Thursday. Weather thwarted that try, but astronauts plan another landing attempt Friday at 5:48 p.m. EDT (2148 GMT) in Florida, though rain and high winds are expected again.

The light show Wednesday was aided by an unusually large amount of water being dumped all at once - about 150 pounds (68 kg), said NASA spokeswoman Kylie Clem. Discovery had just undocked from the International Space Station the day before, and had not been able to unload waste water during the 10-day visit.

"It would have been a large quantity because we don?t do water dumps while docked to the station now," Clem told SPACE.com in an e-mail. "That is a fairly new restriction over the last couple of flights in order to prevent potential contamination of the Kibo module."

The Kibo module is a new Japanese-built research lab on the space station that includes an external platform to expose science experiments to the space environment. Water dumps from a docked shuttle could potentially pollute the experiments.

In general, though, spotting space water dumps from Earth is common, Clem said.

Waste water usually freezes upon jettison into a cloud of tiny ice droplets. Then when the sun hits, the ice sublimates directly into water vapor and disperses in space.

A number of people in North America apparently spotted Wednesday's dump, and some sent pictures to the Web site SpaceWeather.com.

One of them, Abe Megahed, photographed the tail at 9:40 p.m. EDT (0140 GMT) Wednesday from Madison, Wisconsin.

"I just watched the shuttle and station flyover (8:40 PM CST 9/9/09) and was surprised to see that the shuttle was sporting a massive curved plume," he wrote. "What could it be? Something venting? An OMS burn? RCS thrusters? A massive, record breaking urine dump?"

It turns out he wasn't wrong about that last one.

• New Video - Tour the Space Station's Bathroom
• Video - Drinking Water From Space Urine
• New Show - Inside the International Space Station