A mesmerizing display of lights flashing in the night sky over Northern California on Friday was caused by the re-entry of flaming space debris into Earth’s atmosphere, experts said.
In particular, flaming chunks of communications equipment, jettisoned from the International Space Station in February 2020, shot through the sky at 17,000 miles per hour, said Jonathan McDowell, an astrophysicist at the Smithsonian and Harvard Center for Astrophysics.
The equipment trajectory had shrunk in recent years until it was low enough to break apart and burn.
“What you’re seeing are actually very small objects releasing a lot of energy, very high, traveling extremely fast,” he said.
The retired 700-pound communications antenna, called the Inter-orbit Communication System-Exposed Facility, went into space on a shuttle flight in 2009. About 10 percent of such equipment could fall to Earth in small pieces, rather than en route to melt, said Dr. McDowell.
The equipment came down uncontrolled, meaning experts cannot predict exactly where the objects will land. Dr. McDowell said pieces likely landed somewhere around Yosemite National Park. In contrast, the destination of equipment in a controlled de-orbit can be specified using rocket motors, he said.
Equipment the size of the one that created Friday night’s light show re-enters Earth’s atmosphere every few weeks and has done so for 50 years, he said.
“They’re not very common in a particular place, so it’s always new to the people who see it,” said Dr. McDowell. “It’s just another Tuesday to me.”
On Instagram, King Cong Brewery in Sacramento posted a video of the lights darting away, adding: “This flew over the brewery tonight. what do you think? #UFO.”
Debris falling with a clear sky at night can create an engaging light show for observers, said Moriba Jah, an associate professor of aerospace engineering and engineering mechanics at the University of Texas at Austin.
But as the equipment burns, it could pollute the upper layers of the atmosphere, he said. Upon reaching the Earth’s surface, the equipment can also contaminate oceans and land — and even injure humans, though that scenario isn’t common.
Privateer, a company co-founded by Dr. Jah, tracks about 48,000 man-made objects ranging in size from a cell phone to the International Space Station itself. But only about 10 percent of that is functional, he said.
The rest is garbage.
“Mankind is not slowing down to launch things into space,” he said. “I remember a busy year was one launch a month, and right now we’re launching an average of over 12 satellites a week.”