It’s a bit too early for Santa to be doing a pre-Christmas test flight, but that’s what it looked like in the sky over California when a bright flash appeared in the sky around 5:30 a.m. Pacific on Wednesday. Within minutes, West Coasters frantically took to Twitter to post photos and videos of a vivid, lasso-shaped cloud left in the light’s wake.
What was the strange flash? Stockton, California Twitter user @Richifornia, who captured the video above on his dashboard camera while stuck in traffic at an intersection, initially thought it was the rocket that was supposed to launch from Vandenberg Air Force Base in Southern California, but he soon learned that the launch had been scrubbed.
What he realized later was that he had captured footage of a meteor as it passed through the atmosphere, as the American Meteor Society confirmed: It organization received more than 120 reports “of a bright fireball seen above the San Francisco area.”
“I thought it was a rocket launch at first, but then my mind jumped to [a] meteor,” @Richifornia tells Inverse. “I’d never seen one in person before but with how bright it was that’s what first came to mind.”
But what was even more striking was the cloud left behind by the meteor.
Ryan Aylward, a meteorologist at the National Weather Service, tells Inverse that the fact that people spotted this strange phenomenon was a very rare occurrence, because the upper atmosphere was so dry, making it more difficult for clouds to stick around in the atmosphere.
The lasso-shaped cloud, which was seen from Sacramento to San Diego, is called a noctilucent cloud, he says. During the summer, these clouds sometimes form over polar regions. NASA calls them “electric blue wisps that grow on the edge of space.”
They form about 50 miles above Earth’s surface, in a very high section of the atmosphere. This is why, Alywayrd says, spotting one as so many people did that night is pretty rare.
“This region of the atmosphere is normally very dry which doesn’t support widespread cloud formation,” Aylward says. “However, when an object or dust enters this portion of the atmosphere, it can cause the little water vapor that is present to condense and form a cloud. In this case, the dust from the meteor likely helped form the noctilucent cloud.”
Noctilucent clouds are mostly composed of tiny ice crystals, but there’s evidence from NASA’s Aeronomy of Ice in the Mesosphere mission that meteor dust — or as they call it, meteor smoke — is also a key ingredient in these clouds.
When tiny meteors contact the Earth’s atmosphere and disintegrate, they leave tiny dust particles behind that can attract water molecules in a process known as nucleation. Under the right conditions, those tiny particles of “meteor smoke” serve as an anchor for these clouds to form, just as it did over the West Coast on Wednesday.
As for the meteor, well, Alyward says the cloud can’t tell us much about it. All we know is that it passed through that high part of the Earth’s atmosphere as it disintegrated, leaving behind a pick-me-up for California commuters falling asleep in rush hour traffic.