The best sci-fi thriller on HBO Max reveals a deadly cosmic threat

An admiring astronaut stares at the beautiful, looming expanse of Earth as it can only be seen from space. It’s a stunningly peaceful moment — until a cloud of space debris ruins the view and sends him and a fellow astronaut flying right into a dangerous tailspin.

When the movie Gravity — now streaming on HBO Max — came out in 2013, the scientific phenomenon of Kessler Syndrome was largely a topic of discussion among astronomers and other space experts. But as space traffic becomes more congested due to the accumulation of space junk and live satellites, it’s become a phenomenon of increasing concern to the masses. You don’t need to be an astronaut to worry about out-of-control space junk floating around in Earth’s orbit.

But what is Kessler syndrome, how is it a threat to humans, and is Gravity’s portrayal of this space phenomenon scientifically accurate?

According to Harvard astrophysicist Jonathan McDowell, Gravity gets nearly as much wrong as it does right about this complex space phenomenon.

“Gravity was a fun movie,” McDowell tells Inverse. “There was a lot to like about it. And there was a lot to nitpick.”

Reel Science is an Inverse series that reveals the real (and fake) science behind your favorite movies and TV.

What is Kessler syndrome?

In Gravity, lead astronauts Ryan Stone (Sandra Bullock) and Matt Kowalski (George Clooney), are operating in space outside of International Space Station. They’re busy cracking jokes and installing a panel on the Hubble Space Telescope when they get an urgent warning from NASA to abort the mission.

Apparently, the Russians have struck one of their own spy satellites, creating a cloud of debris that is fast approaching the ISS.

As NASA’s Johnson Space Center in Houston (often referred to as “Houston” by the space community) reports in the movie: “Debris from the missile strike has caused a chain reaction, hitting other satellites and creating new debris, traveling faster than a high-speed bullet.”

What Houston is describing here is, essentially, the dangerous, real-life phenomenon of Kessler syndrome.

“The basically turns everything in space into confetti.”

Kessler syndrome “is the idea that you can have a chain reaction of satellite collisions that could make space unusable,” McDowell says.

Here’s how it works. Thousands of fast-moving satellites currently orbit Earth. A big satellite crashes into another satellite, creating thousands of pieces of smaller pieces of debris that are moving at thousands of miles per hour.

“If those pieces of debris then hit other satellites and destroy them, you could get a runaway [reaction] that basically turns everything in space into confetti,” McDowell says.

That’s basically what happens in the movie Gravity — though with much more haste and dramatic flair than would occur in real life.

Is Gravity’s portrayal of Kessler syndrome realistic?

Mere minutes after they get the warning from Houston, the International Space Station is bombarded with space debris.

The scientists see a few small debris pieces before the entire debris cloud — moving at 20,000 miles per hour — strikes their vicinity. One of their team members gets struck down by the debris, while Stone is literally flung into space after debris strikes the arm of the Space Station holding her aloft.

It’s a breathtaking, gripping scene, but is it scientifically accurate? Not exactly.

McDowell says that astronauts doing external repairs on the International Space Station are at risk of being hit by orbiting space debris. The Department of Defense does track larger space debris and coordinates with NASA’s Orbital Debris Program Office, but there are smaller debris pieces that could be fatal for astronauts.

But McDowell’s biggest gripe lies in how the movie portrays Kessler syndrome.

“The main difference between the real Kessler syndrome and the movie is that it plays out much more slowly,” McDowell says.

In the movie, “it's like half an hour and, suddenly, everything in space is shredded.” In real life, “it takes decades,” according to McDowell.

“Kessler Syndrome is a serious but slow-burning threat.”

In an actual Kessler syndrome scenario, two satellites collide, creating debris that eventually hits another satellite. This causes a chain reaction and a debris cloud forms. But that process takes years — a timeframe that’s much longer than the 1-hour-and-31-minute run-time of Gravity.

“The first satellites hit each other, and then years later, some of the debris from that satellite hits another satellite and the total amount of debris slowly increases,” McDowell adds.

But it would have been hard to make a movie where Kessler syndrome plays out as it does in real life. Like climate change, Kessler Syndrome is a serious but slow-burning threat, gradually accumulating dangerous amounts of debris over time.

“[Gravity] made it more tangible to the average person, because we can respond much better to an immediate threat than to a slow threat,” McDowell says.

Is Kessler syndrome a serious threat?

In a word: yes. Gravity’s premise is very similar to a real satellite collision that occurred in November 2021 when Russia tested an anti-satellite weapon against a dead satellite. This created thousands of space debris pieces that “push us just that far, much further down the hill of this rolling chain” of Kessler syndrome, according to McDowell.

There have been documented instances of satellite collisions in the past 15 years, resulting in gradually accumulating space debris that is ever more likely to cause the chain reaction of Kessler Syndrome.

Just last week, the US Space Force reported debris from a Russian satellite struck a Chinese satellite in March 2021, making it the fifth accidental collision between tracked objects in space.

As Inverse reports, there are some 40,000 space objects at least 10-centimeters across being tracked in orbit, and only 5,000 are active satellites, meaning the rest are likely space debris. There are perhaps millions of even smaller pieces of debris that NASA cannot track.

But it’s not just past collisions or existing space debris that increase the likelihood of Kessler syndrome. Increasing space traffic also poses a looming threat.

Starlink — SpaceX’s satellite internet service promising high-speed broadband to anywhere in the world with clear sky access — plans to launch 100,000 satellites in the coming years. This will increase the likelihood of collisions, according to McDowell.

“The collision rate grows as the square of the number of satellites,” he says. “If you have 10 times as many satellites, you will have 100 times as many collisions.”

“Increasing space traffic also poses a looming threat.”

Kessler syndrome is not just a threat to astronauts working on the ISS, but to thousands of satellites that maintain vital communications systems and weather forecasts.

“The worst threat that we worry about is to the astronauts, but you also don't want to lose billions of dollars worth of hardware that either our internet depends (on) or our weather forecasting or climate change studies,” McDowell says.

Fortunately, it seems the newly launched James Webb Space Telescope will be far enough away that most manmade space junk won’t threaten it, so at least one vital space object may be spared from Kessler syndrome.

According to McDowell, scientists are developing methods to eliminate space debris, such as deploying space debris removal trucks, loosely similar to the concept laid out in the 2021 Netflix movie Space Sweepers. Those are near-term goals but they’re not a reality just yet.

In some ways, Gravity is far more relevant now than when it came out in 2013. Even if it’s not totally scientifically accurate, it’s still worth watching to remind us how little control we humans have in space, even over our all garbage, McDowell says.

“The fact that space is just so much bigger and busier, not just in terms of debris, but in terms of active satellites, makes these incidents more serious.”

Gravity is streaming now on HBO Max.