Satellites burning up in our atmosphere may not be as harmless as first thought

• Spacecraft burning up in the atmosphere are leaving behind metal particles.
• Scientists are racing to understand if that affects the climate.
• One risk is that these particles may spark rainbow-colored clouds that damage the ozone layer.

Satellites and spacecraft burning up in our atmosphere are leaving metal particles in the stratosphere — and scientists are worried it could harm our planet.

About 10% of the particles floating around the stratosphere now come from the aerospace industry, and we don't know if this could impact the climate.

One risk is that these new particles could seed polar stratospheric clouds, which are spectacular rainbow-colored clouds that can damage the ozone layer, experts told Business Insider.

"This is a good demonstration of how important it is to have the basic research on the stratosphere," Daniel Murphy, a research scientist at the National Oceanic and Atmospheric Administration Chemical Science Lab, who led a survey of the particles, told BI.

"There is a whole phenomenon here that we didn't expect out and we don't fully understand the implications," he said.

Stratospheric particles can shape the ozone layer

Remember the ozone layer? If you were around in the 80s, that's likely the period you'd associated it with.

This crucial layer of the atmosphere, mostly contained in the stratosphere, protects us from ultraviolet radiation from the sun. It was frequently splashed across the headlines about 40 years ago when scientists raised the alarm about gaping holes growing over the poles made by chlorofluorocarbons (CFCs) rising up uncontrolled to the atmosphere.

The ozone holes are not making the news quite so often today. Thanks to the 1987 Montreal Protocol, a global agreement that set out a trajectory to phase out ozone-damaging gases, they have been steadily healing.

Still, they are not gone. In September 2023, the hole above the Antarctic grew to its sixth-biggest size ever observed before snapping back, likely because of the particles spewed by the Hunga Tonga underwater volcano eruption in 2022.

That's why it's important to keep an eye on particles in the stratosphere. These nanometer-sized flecks, which naturally come from meteors crashing into the planet, can dramatically change the stratosphere's chemistry.

Clouds don't usually tend to form in the stratosphere, because it's much drier than the troposphere, where most clouds are born.

By bringing in elements you wouldn't usually see in the sky, like metals, these particles can combine with the sulfuric acid naturally present in the stratosphere to create a chemical reaction that can suck up passing water vapor, creating an ice crystal.

That, in turn, can spark a chain reaction that creates rainbow-colored polar stratospheric clouds.

On their own, these stunning clouds are harmless, but they can be terrifying when mixed with human-made gases. The clouds' edges offer perfect conditions to turn damaging chlorines and bromides into their active, ozone-busting form.

Metal from satellites and spacecraft is vaporizing into the atmosphere

Murphy and his colleagues recently conducted a survey of the state of stratospheric particles over Alaska using a sensitive detector aboard NASA's WB-57 high-altitude research plane.

The findings, published in the peer-reviewed journal PNAS in October 2023, revealed that about 10% of the stratospheric sulfuric acid particles they picked up could not be explained by natural causes.

"We weren't really looking for spacecraft, but it became apparent in the data that there were elements that couldn't be coming from the meteors," Murphy told BI.

The particles contained "far too much aluminum, far too much lithium, far too much of a few other elements to be coming from meteors," he said.

Two elements found in the particles, niobium and hafnium, were particularly surprising, Murphy said.

These don't occur naturally, but have to be refined, the scientists said.

"The combination of aluminum and copper, plus niobium and hafnium, which are used in heat-resistant, high-performance alloys, pointed us to the aerospace industry," Murphy added.

Right now, we simply don't know what these new particles could do. But scientists are eager to figure it out.

"This is a new problem and we're just beginning to understand it," said Murphy.

They may be able to spark polar stratospheric clouds. If so, this could be a big problem in the short term, Martin Chipperfield, a professor of atmospheric sciences from the University of Leeds, UK, told BI.

"The timescale for the ozone hole to disappear is about 2060 based on current predictions because the chlorine is going down very, very slowly," said Chipperfield, who was not involved in the study.

"So that still gives plenty of scope in the short term, if we greatly increase the burnout of space debris over next couple of decades, for the ozone hole get worse before it gets better," he said.

These new particles could also migrate to the troposphere, where they might influence the formation of feathery cirrus clouds. Unlike other clouds, cirrus clouds retain heat in our atmosphere, which could worsen the climate crisis.

It's also possible that the particles could create a completely new phenomenon. Or they could do nothing at all.

Their composition is unique, so it's unclear what to expect. Murphy said scientists will have to do experiments in the lab to test this out.

"It's very important to understand it because the space industry is growing so rapidly," Murphy told BI.

"If there are impacts, you'd rather understand it now before it grows than after it's already grown a lot."

We're realizing how little we know

With launch costs going down, the number of satellites orbiting the planet is only expected to grow to over 50,000 by 2030, up from about 8,000 now. Many of these satellites are expected to have a short lifetime.

"If you multiply those numbers out, a satellite will be reentering the atmosphere on average about once an hour," said Murphy.

Within the next few decades, Murphy and his co-authors estimate aerospace debris could make up 50% of the particles in the stratosphere, which makes the need to understand what they do even more pressing.

Spacecraft decommissioning is only part of the equation, said Chipperfield.

"There's an increasing number of rocket launches for small satellites and tourism, which burn kerosene or other fuels that emissions in the atmosphere. Then some satellites and orbit have fuel like iodine that can come back to the atmosphere. And then the demise," he said.

"I think the whole life cycle of satellites is definitely one to watch, and this burn up is part of that," said Chipperfield.

Scientists are also seriously considering geoengineering the atmosphere to help shield our planet from the heat of the sun by sending billions of particles of sulfuric acid into the stratosphere.

For Murphy, this all goes to show just how little we know about how humans are affecting the stratosphere as more forays are reaching for the skies.

"That there was still a surprise in our understanding of the composition of particles in the stratosphere is relevant to conversations about adding more," said Murphy.