In 2005, former U.S. astronaut and International Space Station Commander Leroy Chiao was out on his final spacewalk, when something unusual caught his eye.

There appeared to be five lights flying by him in formation, with one light slightly further ahead.

Chiao called to his crewmate who was also out on a spacewalk at the time, and asked him if he had seen the flying objects.

“He said he didn’t, and then we went into sunlight and everything vanished,” Chiao told CTV’s Canada AM.

His story piqued the interest of aerospace engineer James Smith, who examined satellite images and confirmed that lights could be seen in the same spot Chiao had been flying.

Smith then looked at satellite paths and army testing records for an explanation, but found nothing.

After looking at commercial fishing vessel lights in the ocean, Smith determined that Chiao had witnessed a line of fishing boats off the cost of South America, which were using bright lights to attract squid.

But because it was twilight time, Chiao said the “rotation of the Earth made them appear to fly by.”

“I’ve had my share of things that I’ve seen that seemed odd at the time, but every one of them has been explained,” he said.

And while Chiao likely didn’t see aliens fly by him in 2005, he still firmly believes there is other life out there.

“I believe the universe is basically infinite, so you have accountably infinite number of planets out there somewhere that could support life as we know it,” he said. “I think it’s pretty arrogant to believe that we’re the only life in this entire universe.”

Chiao is part of a group of former astronauts who have shared their stories of strange and unexplained moments in space for Discovery’s new four-part series titled “NASA’s Unexplained Files,” which premiers Monday, May 26 at 9 p.m. ET.