Northern lights enthusiasts were treated to a surprise while watching the green bands of light dance in the Alaska skies: a light baby blue spiral resembling a galaxy appeared for a few minutes among the aurora.

The cause was a little more mundane than an alien invasion or the appearance of a portal to the far reaches of the universe early Saturday morning.

It was simply leftover fuel from a SpaceX rocket that took off from California about three hours earlier.

Alaska sky spiral caused by SpaceX fuel dump
TOPSHOT-FINLAND-ARCTIC-NORTHERN LIGHTS
(Photo : IRENE STACHON/Lehtikuva/AFP via Getty Images)

According to space physicist Don Hampton, a research associate professor at the University of Alaska Fairbanks Geophysical Institute, sometimes rockets have fuel that needs to be discarded, as per Phys.org.

He said that when they do this at high altitudes, the fuel freezes.

And if it happens to be in the sunlight, you can see it as a sort of big cloud, sometimes swirly, when you're in the darkness on the ground.

While not a common occurrence, Hampton claimed to have witnessed it three times.

The appearance of the swirl was captured in time-lapse on the Geophysical Institute's all-sky camera and widely shared online, causing a bit of an internet storm, according to Hampton.

Photographers who went to see the northern lights also shared their images on social media.

This all happened as it passed over Alaska during a beautiful aurora display, stunning many night-watchers, including myself, according to professional photographer Todd Salat, known for stunning aurora images, in an email to The Associated Press.

The rocket lifted off from Vandenberg Space Force Base in California on Friday night, carrying approximately 25 satellites as payload.

Because of the timing of the fuel dump and the fact that it was a polar launch, the blue spiral could be seen across a large swath of Alaska.

"And we've got that really cool-looking spiral thing," Salat added.

Another spiral was seen in January, this time over Hawaii's Big Island.

A camera on the summit of Mauna Kea, outside the Subaru telescope of the National Astronomical Observatory of Japan, captured a spiral swirling through the night sky.

Also Read: SpaceX Rocket Fumes are Hazardous to Both Humans and the Climate: Scientists Issue Warning

Effects of SpaceX

Through the development of reusable rockets, SpaceX has made significant strides in reducing the environmental impact of space launches, as per the Smithsonian Magazine.

The Falcon Heavy rocket can carry 68 tonnes of equipment into low-Earth orbit and has been advertised as costing around US$1,300 per kg of payload, whereas the space shuttle cost around US$60,000 per kg.

This recovery significantly reduces the cost of launch for both exploration and scientific discovery.

However, environmental concerns remain associated with SpaceX's operations. Falcon Heavy's current fuel is RP-1 (refined kerosene) and liquid oxygen, which produces a lot of carbon dioxide when burned.

Three Falcon 9 rockets contain approximately 440 tonnes of kerosene, and RP-1 contains 34% carbon.

While this amount of carbon is minor in comparison to global industrial emissions, it is still a cause for concern.

While SpaceX has made significant progress in reducing the environmental impact of space launches by developing reusable rockets, there are still concerns about the carbon emissions associated with its operations.

It is important to note, however, that these emissions are minor in comparison to global industrial emissions.

Related article: SpaceX Going Big: Elon Musk Company Begins Test Firing Parts, Boosters of Falcon Heavy