This article originally appeared on VICE US.
NASA set the Arctic Circle ablaze last week with colorful blue vapor clouds that were seen above parts of Finland and Norway. And yes, they did cause some people to ask: Aliens?
The apparition was caused by a NASA rocket launch that discharged “gas tracers” into the sky to probe the mechanisms behind auroras. The Saturday mission, named “AZURE” for the Auroral Zone Upwelling Rocket Experiment, launched from Norway’s Andøya Space Center just after midnight local time, and after several attempts in 2018 were scuttled due to bad weather.
Not unpredictably, the vibrant particle clouds conjured (short-lived) visions of extraterrestrials by some who witnessed the event.
“We saw two orange dots rise into the sky and disappear,” photographer Michael Theusner told Forbes. “A short while later strange lights and colorful, expanding clouds appeared I first did not have an explanation for. It looked like an alien attack.”
NASA’s Wallops Flight Facility in Virginia, which supports the AZURE mission, said it didn’t receive any questions about the launch.
“When we do these types of tests at Wallops we do conduct notifications for people from the mid-Atlantic to the northeast United States,” a NASA spokesperson told Motherboard in an email. “It’s not uncommon to see comments [about aliens] since these tests can be highly visible.”
Between 71 and 155 miles above Earth, the rockets deployed trimethyl aluminum and a mixture of barium and strontium (think: fireworks ingredients) to illuminate the flow of kinetic and thermal energy—components of an aurora that aren’t easily seen with the naked eye. Both rockets ultimately soared 200 miles high at their apex.
“Such measurements are critical if we are to truly understand the effects of the mysterious yet beautiful aurora,” NASA said.