NASA has quelled fears of an alien invasion after strange pulsating lights were spotted over the Arctic.

Mesmerizing videos show glowing clouds shimmering over northern Sweden that some online commenters claimed was a UFO light show.

But the space conundrum has a far simpler explanation.

A pair of specially designed rockets launched by the space agency last week released colorful chemicals into the sky.

Fired from a base in Finland, the rockets were the first of eight planned launches from the Auroral Zone Upwelling Rocket Experiment or AZURE.

It aims to help NASA understand the Northern Lights and the role they play in Earth’s energy systems.

Traveling 200 miles to their target, the rockets released their payload in the sky during a real aurora to track how particles flow through Earth’s atmosphere.

It is thought that the movement of energetic particles through a layer of the atmosphere called the ionosphere is what causes the Northern Lights.

Once released from the rockets, the gas fell and ionized to produce clouds of color that gave scientists an idea of the movement of particles.

It also gave onlookers on the ground a great view and many of them posted clips to social media.

Some were left a little confused by the experiment, which made it look like an advanced race had made its way to our planet.

“Residents for hundreds of miles were taken by surprise by these strange lights,” according to Chris Nation, who runs the Aurora Addicts guiding service.

“The lights prompted calls to the police and ‘The aliens are coming!’ hysteria!”

Alien hunter Scott C Waring, who runs the crackpot site UFO Sightings Daily, said: “A person walked out onto their patio and expected to see the aurora borealis, but instead caught sight of a UFO fleet coming in for a landing as they entered an underground base.”

NASA scientists hope the experiments will help them better understand how the Northern Lights appear in the sky.

“By tracking the movement of these colorful clouds via ground-based photography and triangulating their moment-by-moment position in three dimensions, AZURE will provide valuable data on the vertical and horizontal flow of particles,” explained Miles Hatfield from NASA’s Goddard Space Center in the US.

“Such measurements are critical if we are to truly understand the effects of the mysterious yet beautiful aurora.

“The results will be key to a better understanding of the effects of auroral forcing on the atmosphere, including how and where the auroral energy is deposited.”