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Thousands of Falling Satellites Put the Atmosphere at Risk

By Eric RostonSana PashankarHayley WarrenJin Wu for Bloomberg Green + The Big Take May 1, 2025

Daily life increasingly depends on systems of satellites orbiting Earth. As fleets proliferate, ever greater numbers of expired units will hurtle back toward the surface.

Decommissioned satellites vaporize when they plunge through the atmosphere, decomposing into their elements, mostly aluminum, with some copper and lithium.

That’s changing the atmosphere in ways that threaten the Earth’s protective ozone layer.

Observed from Earth, these reentries look like shooting stars, blazing across the sky.

However amazing to behold, this is becoming a bigger issue. In 2024, there were about 1,000 satellite reentries, equivalent to three per day.

The wild growth rate of satellites in orbit, driven by companies like SpaceX, is expected to lead to as many as 25 to 50* reentries per day by 2035, creating a new delivery mechanism for pollutants damaging to the Earth’s protective shield.
* Estimation by Harvard astrophysicist Jonathan McDowell

Elon Musk’s SpaceX has more than 7,000 satellites in orbit to create its Starlink internet constellation. The company has said in the past that it plans to have as many as 42,000 units aloft, each with a roughly five-year life expectancy.

To maintain a fleet that size, astrophysicist Jonathan McDowell estimates the company will need to launch the equivalent of 23 satellites a day — and boot the same number out of orbit, to burn up at the top of the atmosphere.

SpaceX is the most prodigious launcher, but it’s far from the only company looking to fill space. On Monday, Amazon.com Inc.’s Project Kuiper put its first 27 production satellites into orbit as Executive Chairman Jeff Bezos looks to build out an internet constellation to compete against Starlink.

Last year, more than 2,800 satellites were deployed compared to 500 in 2019, according to an analysis by McDowell, who works at the Harvard & Smithsonian Center for Astrophysics and also privately publishes data on space launches and satellites.

Satellites in low-Earth orbit eventually have to come down, and companies rely on the upper atmosphere to act as a waste incinerator. That’s exposed a blind spot in environmental laws: They only deal with pollution from human activities near Earth’s surface. But just as carbon dioxide and ozone-destroying compounds drifting up have created problems, so too can pollutants raining down at ever-increasing rates.

Studying stratospheric pollution is a burgeoning field. The first wave of research that started about 5 years ago shows that dosing the atmosphere with soot from rocket fuel and particles of reentering satellites might set back decades of progress repairing the ozone layer and indirectly alter the weather.

The satellite industry boom could exacerbate the effects scientists have observed. In the next five years, the number of satellites in orbit is projected to grow from roughly 12,000 today to between nearly 60,000 and 100,000. By 2035, Goldman Sachs projects that the value of the satellite industry will reach $108 billion, up from $15 billion today.

“We’re right now at that point that we see there is a problem coming,” said Kostas Tsigaridis, a research scientist at Columbia University’s Center for Climate Systems Research.

Low-Earth orbit satellites are designed to burn up in the atmosphere. But the problem with treating spacecraft as disposable is that the garbage still has to go somewhere, just as it does with industrial waste or consumer products.

In the case of satellites, particles are ending up in the atmosphere. The amount of material hanging atop the atmosphere isn’t a problem yet, but it’s giving atmospheric scientists a case of déjà vu.

Seen This Show Before

Experiments in the 1970s showed that factors from supersonic jets to chemicals used in spray cans and refrigeration destroyed ozone, a compound that sits in the stratosphere and blocks harmful ultraviolet light from reaching Earth’s surface. In 1985, scientists discovered a massive hole in the ozone layer. Governments, industries and the scientific community worked together quickly to ban the troublesome chemicals. The hole was much smaller than the long-term average in 2024 and, at current rates, it could recover fully by the mid-2060s.

But satellites are now putting a significant global environmental success story in jeopardy.

Martin Ross, senior project engineer at the Aerospace Corporation, was one of the first to sound the alarm. He co-authored articles in Scientific American and Eos warning of increased pollution from a quickly growing industry. And “unlike with aviation, emissions produced by the space industry affect every layer of the atmosphere,” he and science journalist Leonard David wrote in 2020.

Researchers began to analyze the impacts in the late 2010s, but they couldn’t yet see the satellite boom just around the corner. Scientists at University College London looked at the possible atmospheric effects of the space industry’s 2019 data, which just missed the acceleration of launches. Looking at data from 2020 to 2022, however, they could already see the new trend.

“We were surprised by how quickly those numbers were growing,” said Connor Barker, a UCL research fellow in atmospheric chemistry, referring to the number of launches going up and debris coming down.

WHAT GOES UP . . .

Satellites’ impact on the ozone layer begins before they’re even in orbit, driven by the rocket trip to get them there. Kerosene used to power many launches burns more inefficiently the higher rockets climb. That leads to soot pollution, or black carbon.

Closer to Earth, climate scientists know that soot settles on ice caps and mountain glaciers that top out at roughly 4,500 meters (15,000 feet). At those lofty heights, it absorbs heat and accelerates glacial melt.

The satellite boom, though, is taking soot higher still. About 80% of the black carbon generated by rocket launches is deposited 15 kilometers or higher above the Earth’s surface. At the top of the atmosphere, it might have a warming effect 500 times greater than the same amount at ground-level, according to a 2022 study.

Effects on climate change might be indirect and are so far little-studied. But high-altitude soot could shift large-scale circulation patterns and how some clouds form, said Eloise Marais, a professor of atmospheric chemistry and air quality at University College London. Stratospheric black carbon can also absorb sunlight, reducing the amount reaching the surface and cooling the planet slightly.

That’s basically geoengineering, she said, “a band-aid solution to anthropogenic warming that the world is very hesitant to adopt, due to potentially severe unintended environmental consequences.”

An emerging concern, though, is soot’s ability to accelerate ozone destruction by heating what’s known as the tropopause, a boundary of cooler air that separates the lower atmosphere from the stratosphere. The added heat from soot could create a “leak,” allowing water vapor to rise into the stratosphere where it would warm things up further and contribute to other forms of ozone destruction, according to a 2024 working paper led by Tsigaridis.

. . . MUST COME DOWN

Scientists are continually improving data of spaceflight’s impact on the atmosphere. A 2023 study for the first time put a number on the amount of stratospheric aerosols already containing launch- or reentry-related particles, finding that it’s 10% and likely to grow with the industry.

They’re also tracking a wider variety of novel chemicals in the upper atmosphere that may not have been there before. Recently spotted elements include copper, lead and lithium there because of satellite vaporization and surpassing levels deposited by cosmic dust, according to that 2023 paper.

“No one expected lithium to be in there,” said Christopher Maloney, a research scientist at the University of Colorado Boulder.

The rising amount of aluminum material, though, is most concerning. The metal is one of the main materials used to make rockets and satellites, but the precise amount used isn’t known due to trade secrets and a lack of disclosure regulations. Estimates vary wildly, though the most common range is 35% to 45%.

Stratospheric aluminum combines with oxygen to make aluminum oxide, or alumina. That compound can enable ozone destruction through a series of chemical reactions.

Falling satellites in 2022 produced about 17 tons of alumina, a 30% increase over natural levels. Fully realized “mega-constellations” of 550-pound satellites, which might be 30% aluminum, could add 360 tons a year, likely enough to harm the ozone layer, according to a 2024 paper.

“We don’t know, really know, what the particles look like from reentry of alumina because we don’t have any experimental data for that,” Barker said. “How big those particles are will affect how quickly they fall down. And that affects their environmental impact.”

Maloney’s recent work has analyzed what might happen to thousands of metric tons of alumina in the stratosphere. The trouble is, there’s a lot of missing data, including the size of the aerosol particles, which are less than a millionth of a meter. It takes the stratosphere several years to clean itself as air descends at the poles.

Maloney called understanding alumina “one of the biggest challenges when it comes to looking in the middle and upper atmosphere.”

Beyond the particles, the heat generated from destroying satellites rearranges the atmosphere in a way that threatens ozone. Temperatures can reach up to 3,500F (1,925C), high enough to break up the nitrogen molecules that make up 80% of the atmosphere. The atoms recombine with oxygen into nitrogen dioxide, referred to as NOx. Under the right conditions, a molecule of NOx can destroy an ozone molecule before regenerating and moving on to “attack another ozone molecule,” said Laura Revell, an atmospheric scientist at the University of Canterbury, in Christchurch, New Zealand.

The exact role each of these processes plays in depleting ozone aloft is still being teased out, mostly in simulations. Scientists will get some much-needed clarity from the atmosphere soon: The European Space Agency plans to launch a mission in 2027 that would follow a satellite’s final descent into the atmosphere and sniff out what’s left in its wake.

Satellites generated $285 billion in 2023 — or more than 70% of all space-related revenue — according to the Satellite Industry Association. Business is expected to boom even further as launch costs fall and demand for services from imagery to wireless internet rises.

Along with SpaceX, companies and governments — from Canada-based firm Telesat Corp. to the European Union — are working to build constellations with thousands of satellites. Amazon’s Project Kuiper plans to launch more than 3,000.

The backlash to Musk’s embrace of President Donald Trump could also help rivals expand their reach.

“A lot of our customers say, ‘We want alternatives, we don’t want to be caught in a potential monopoly situation with a single supplier,’” said Eva Berneke, the CEO of Eutelsat, which operates one of the only other constellations besides Starlink that provide internet from low-Earth orbit.

Major satellite companies are aware of the growing body of research on the risks associated with reentries, though it’s not yet clear how regulation might evolve in response or how that could impact the industry or the costs of launches.

“​​I don’t think this data, this analysis is concrete, robust, or has been done enough to be definitive yet,” said Chris Jones, vice president of network operations at Iridium, a satellite communication services provider.

US regulations favor burning up satellites in the atmosphere. The Federal Communications Commission defines successful disposal for spacecraft in or passing through low-Earth orbit as atmospheric reentry no later than five years following the end of their mission.

There are alternatives, though, like sending defunct satellites into a so-called “graveyard orbit,” a high-altitude resting place away from operational space vehicles. Communications firm Globalstar previously relied on this approach but has since shifted to disposing of satellites in the atmosphere following the change in regulation.

“We participate in regulatory proceedings and ask ‘Are you sure that this is the best way to handle satellites at end of life?’” said Barbee Ponder, Globalstar General Counsel and Vice President of Regulatory Affairs. “And we’ve been told ‘If you want a license to operate, this is how you’ve got to proceed.’”

Another way to mitigate the environmental impacts is to swap out aluminum components. Iridium’s Jones says this is already happening as the industry transitions from large, heavily metal satellites like those built in the 1970s and 1980s to more cost-effective, smaller versions made increasingly out of carbon fiber, the stratospheric implications of which haven’t been tested yet.

But mainly, satellite companies are prioritizing the use of materials most likely to be incinerated rather than falling back to Earth.

Chunks of satellites that survive reentry have the potential to damage buildings and hurt people, a huge liability for companies. As the number of reentries increases, so too has debris reaching the surface. In the past year alone, high-profile incidents have seen space junk fall on a village in Kenya, a farm in Canada and a home in Florida.

“When we’re designing the satellites, we want to design them to be as demisable as possible,” Ponder said. “We try to minimize the use of certain metals such as titanium, which have the possibility of surviving reentry.”

Squeezing more life out of satellites can reduce reentries. It also offers another benefit to companies: It’s cheaper.

Telesat favors longer-lasting equipment that can reduce both the number of launches and the volume of expired satellites, said Michel Forest, chief technology officer at Telesat. “This is a strategy that is fully aligned with sustainability, but also to be frank, this is also to be cost-effective in terms of investment.”

Other ideas include Japan’s mostly wooden satellite concept and a system to collect satellites in space and reprocess their metal components into new ones. But reusing satellites hasn’t yet proven to be cost-effective, Jones of Iridium said.

“That’s very science fiction-y, but it’s what you have to start considering if you can’t bring them back through the atmosphere,” McDowell said.

Ultimately, however, companies seem to be in no rush to rethink their business model based on research to date. And neither do regulators.

“We don’t have to ultimately choose between deregulation and those responsibilities for space sustainability and the environment and so forth,” the FCC’s Space Bureau chief Jay Schwarz said in early April, when asked about the environmental impacts of satellite reentry at a conference in Colorado Springs.

In a 2022 report, the United States Government Accountability Office flagged that new regulations would likely need to be developed. The office concluded that satellite reentry emissions could change the temperature of the stratosphere and deplete the ozone layer, though it acknowledged more information was needed “to determine how significant these effects may be.”

According to McDowell, research isn’t yet definitive enough to prompt governments or regulators to act.

“It really hasn’t gotten to that point yet,” McDowell said. “The thing the government should be doing right now, in my opinion, is aggressively funding the research.”

While the satellites are unlikely to pose as big a risk to the ozone as refrigerants and spray cans in the 1980s, they’re “going to become more of a problem,” said Columbia’s Tsigaridis. “We should just not close our eyes now because it is small.”