Rocket Junk Streaked Spectacularly Across the Pacific Northwest Sky; Here's the Science Behind the Show

A SpaceX rocket booster falling out of orbit made for a spectacular display over much of the Pacific Northwest on Thursday night, prompting calls to authorities and excited posts to social media. This video was recorded by CT Publishing Vice President Franklin Taylor.
Franklin Taylor / The Chronicle

Genevieve Reaume was outside her Portland home walking her six-month-old puppy Thursday evening when she saw in the sky a fast-moving shower of glowing points of fire.

"It was right over our heads and it was just these streaks of light," said Reaume, a TV reporter at KATU in Portland. "We're standing in the middle of the street, watching this crazy light show above our heads, wondering: What in the world are we witnessing?"

From the big windows in her home between south Seattle and Renton, Michelle Zimmerman, principal and teacher at Renton Prep Christian School, has a view of the planes coming and going at Seattle-Tacoma International Airport.

Hearing what she thought could be explosions, she looked out and also saw the extraordinary sight: "a bunch of cool, glowing lights moving quickly and horizontally in our window view from right to left."

"It did look really beautiful because it had kind of like a sparkly look, metallic brush strokes painted in the sky," she said.

All over the Pacific Northwest, anyone lucky enough to be outside at 9 p.m. on Thursday witnessed something remarkable: For about 40 seconds, a cloud of fiery objects streaked  across the heavens, trailing parallel tails of fire.

It was bits of a SpaceX rocket crashing back to Earth, but at the time it was a cosmic mystery.

"We were awe-struck," said Reaume. "Completely swept up and overwhelmed with what we were seeing."

"Of course being a news reporter, the first thing I do is grab my phone," she said. Videos of the celestial apparition quickly went viral on social media.

In ancient times, such an event would surely have been interpreted as an augur of something very significant, the birth of a king, or a god roused to anger.

Even in modern minds, delusions of an apocalypse or  an alien invasion surfaced Thursday on social media.

More sensible residents of this region grasped in the moment for other explanations.

"I'm not like, 'It was an alien invasion,' but it was something that was not man-made, was my initial guess ... some sort of rare astrological event," said Reaume. "But in my heart I knew it wasn't a comet or a shooting star because it just lasted way too long. I had no idea what it was."

Zimmerman and her parents, watching the event play out in the sky above Sea-Tac airport, feared an airplane catastrophe.

"We were scared that something either hit a plane or there was a collision... because it initially looked like something had exploded," she said. "We were hoping that there were no people on board."

Reaume's guess that the phenomenon couldn't be man-made was mistaken. And thankfully so was Zimmerman's fear of human tragedy.

This beautiful, extraordinary show had a more prosaic and benign explanation: It was space junk falling out of orbit, moving at around 17,000 miles per hour as it burned up in the atmosphere and fell toward earth.

Jonathan McDowell, an astronomer at the Center for Astrophysics, Harvard & Smithsonian, in Cambridge, Massachusetts, said its trajectory means if any small pieces fell to earth they will have fallen in the mountains around the border between Montana and Canada — almost certainly without doing any harm on the ground.

To be precise, what disintegrated over our skies was the approximately 45-foot-long, three-ton second stage of a Falcon 9 rocket launched by SpaceX from the  Kennedy Space Center in Florida on March 4.

After that rocket safely delivered into orbit the latest batch of 60 SpaceX Starlink satellites, built in Redmond, SpaceX engineers were supposed to execute a controlled deorbit — but something went wrong.

Rather than such a quick controlled descent, two days after launch the Falcon rocket stage was added to the U.S. Space Force's catalog of man-made space objects spinning around our planet, the 47,782nd such object since the  Soviet Union sent up Sputnik in 1957.

Astronomers, including McDowell, had been keeping an eye on it in the three weeks after its launch as it gradually spiraled downward, slowly edging back into the atmosphere.

After the fiery light show, both Reaume and Zimmerman saw a tweet that McDowell posted within 20 minutes of the event, explaining  what they had seen.

"I reposted that, because I saw people saying oh, it's an alien or the end of the world coming," said Zimmerman. "I wanted to reshare the science."

Here's the science, as McDowell laid it out in an interview Friday.

When a rocket is launched into space, an enormous first-stage rocket powers it up off the earth, then falls away. While NASA typically has these fall into the ocean, SpaceX famously has pioneered returning those first-stage rockets to Earth by controlling their descent with engine bursts. They land upright, ready for re-use — a remarkable feat of engineering matched by Seattle's rival space rocket company, Blue Origin.

Even as the first stage falls away, the smaller second stage of a space rocket ignites and boosts the payload into orbit. Once in orbit, the rocket releases its cargo of satellites or whatever it's carrying aloft.

That second stage of the rocket travels "at least three times faster than the first stage ever gets, and so it has 10 times the energy," McDowell said. "That's why it's a lot harder to solve the problem of  bringing it back and using it again. They haven't solved that one yet."

Left to its own devices, any piece of metal equipment in orbit will gradually be slowed down by the friction of the air, even in the very thin atmosphere 300 miles up. Its circular orbit will spiral inward until at a height of about 60 miles above the earth it encounters an atmosphere that, with the friction from traveling at such high speed, will cause it to heat up thousands of degrees.

Without some heat shield like the one that protected the Space Shuttle, metal melts — and the gear breaks up as  it "re-enters" the atmosphere.

"It is not unheard of for there to be sonic booms in this situation," McDowell said, potentially explaining what drew Zimmerman to her window.

If it's a large enough piece of space junk, he added, "you've got a several-ton object burning up in the atmosphere and there's some small chance that some of the denser chunks of it don't melt entirely, but survive and then hit the ground."

In this case, "Most of it will have melted and burned up in the upper atmosphere," McDowell said. "It was heading over sort of the Tacoma area, heading east ... By the time that it really hit the ground it will be very small amounts of metal scattered over a 100-mile track near the Montana/Canada border, I would say, in the mountains."

He said there's no record of anyone being hit by space debris and that the chances of it happening are generally thought to be low.

There are currently about 20,000 man-made objects orbiting earth today. Only 4,000 or so are working satellites, the rest classified as space junk that at some point will spiral down and re-enter.

He recalled that in 1979 the 70-ton Skylab space station came crashing down on Australia.

"We don't like that," McDowell said. "But a three-ton rocket stage is not a big deal."

Still, he said, to reduce any risk, best practice is to control the re-entry of space junk.

That's done by precisely firing a rocket burst to change its circular orbit to an elliptical one that arcs from a point perhaps 300 miles above the earth and moves as close to 20 miles to 40 miles above the earth.

"So then as it orbits around, half an orbit later ... it's gonna slam into the atmosphere at a specific predictable point in time," said McDowell. "It's going to break up, disintegrate and burn, but you make it happen at a particular location that you control."

Somehow, SpaceX failed to do that this time. The company did not respond to a request for information Friday. It posted nothing about Thursday's incident on its website, and its CEO and inveterate tweeter Elon Musk didn't mention it on his social media.

SpaceX is "famously tight lipped about pretty much everything," said McDowell. Since the launch in early March, "they've said nothing."

Still, there's no doubt exactly what this was. McDowell and other astronomers have been predicting it. On March 9, he tweeted his estimate that the Falcon 9 rocket's second stage would come to earth in "a few weeks."

However, because the rocket stage was just spiraling down slowly, skimming across the atmosphere almost horizontally at fantastic speed, it wasn't possible to predict exactly when and where it would burn up.

"Two days ago, we knew this rocket stage was going to re-enter, but we didn't know when within 12 hours or so. And it's traveling at 17,000 miles an hour, so if you don't know when within 12 hours, then you don't know where."

As soon as he heard the first reports from the Pacific Northwest on Thursday, McDowell rushed to the orbital data to calculate where it would have been and saw at once that this was the rocket stage he'd been tracking.

Though this explains what people saw in the sky, it doesn't quite capture the experience of watching it and not knowing what it was.

"I see a lot of cool things," said Reaume, the Portland TV reporter. "The Pacific Northwest has great skies and beautiful stars out in eastern Oregon. I've seen the eclipse."

"But there's truly nothing that had me in awe like what happened last night," she said.