Giant spiral appears in Alaska sky

Aurora watchers in Alaska were startled early Saturday morning when a huge spiral appeared in the sky. People quickly posted photos on social media and speculated on what caused the bluish-white shape to show up against the background of a green auroral display. The all-sky camera at Poker Flat Research Range also captured it on video.

Reporters learned about the phenomenon and were soon contacting Rod Boyce, GI public information officer, to ask what the GI might know about it. He reached out to geophysicist Don Hampton, Poker Flat Rocket Range chief scientist.

“Based on some similar events we have seen in the last few years, we expected that this was due to a rocket launch," Hampton said. "We learned that SpaceX had launched one of their Falcon 9 rockets into a polar orbit about two hours earlier, and watching a replay of their live feed showed the trajectory going right over Alaska.”

“The cloud showed up after they had deployed all of their payloads, so it is likely either exhaust from a rocket burn to bring the second stage down over the Pacific, or perhaps dumping extra rocket fuel after that burn. The spiral pattern indicates that the second stage was spinning when it exhausted the gasses. Any water vapor would turn into ice at these altitudes, and the ice would reflect sunlight where the rocket was, and make a bright cloud visible on the ground in Alaska where the sun was well below the horizon. It looks really bright in those picture, but it is likely just a few pounds of water.”

Perhaps a more mundane explanation than a space-time continuum or an alien invasion but nevertheless attention-grabbing.

“I wish there was this much attention for a science event!” Hampton said later. It led to all sorts of news coverage — below is a sampling.

Anchorage Daily News: Mysterious spiral in the sky

Fairbanks Daily News-Miner article: Aurora-lit spiral in the sky

National Public Radio: Stargazers in Alaska recently saw a rare sight

Associated Press: Odd spiral appears amid northern lights

BBC: Mystery spiral captivates aurora spectators

Washington Post: Mysterious spiral over Alaska