Aurora lovers were in for a surprise, mingling with streaks of green light dancing in the Alaskan sky: a galaxy-like light blue spiral appeared in the middle of the aurora borealis for a few moments. The reason early Saturday morning was a little more mundane than an alien invasion or the emergence of a portal to the far reaches of the universe. This was excess fuel from a SpaceX rocket launched from California about three hours ago.

Space physicist Don Hampton, an associate professor at the University of Alaska’s Fairbanks Geophysics Institute, said sometimes rockets have fuel that needs to be fired.

“When they do it at high altitude, that fuel turns into ice,” he said. “And if it’s in the sunlight, when it’s dark on the ground, you can sometimes see it like a big cloud swirling around you.”

While not a common occurrence, Hampton said he’s seen this happen about three times. The view of the vortex was captured in slow motion by the Geophysics Institute’s Global Survey Camera and was widely shared. “This has created a spiral internet storm,” Hampton said. Photographers who came to the Northern Lights show also published the photos they took on social media.

Professional photographer Todd Salat, known for his stunning aurora images, said in an email to the Associated Press, “This all happened while flying over Alaska during a spectacular aurora that has astonished many night watchers, myself included.”

“Believe me, I was totally confused at first,” he said. “Now I know this can be rocket-explained, but I really enjoyed the mysterious feeling of the unknown during and immediately after the experience.”

The rocket took off from Vandenberg Space Force Base in California on Friday evening, with about 25 satellites as payloads. The timing of the fuel dump and the fact that it was a polar launch made the blue spiral visible over the vast area of ​​Alaska. “And we have a really cool spiral thing,” Salat said.

In January, another spiral was detected, this time over the Big Island in Hawaii. A camera atop Mauna Kea, near Japan’s National Astronomical Observatory’s Subaru Telescope, captured the swirling spiral across the night sky. Researchers say this is the result of a military GPS satellite previously launched by a SpaceX rocket over Florida.