Satellite ‘megaconstellations’ could jeopardize recovery from ozone hole

When old satellites fall into Earth’s atmosphere and burn up, they leave behind tiny particles of aluminum oxide that eat away at Earth’s protective ozone layer. A new study finds that these oxides increased 8-fold between 2016 and 2022 and will continue to accumulate as the number of satellites in low Earth orbit skyrockets.

The study is published in the journal Geophysical research letters.

The 1987 Montreal Protocol successfully regulated ozone-damaging CFCs to protect the ozone layer, thereby reducing the ozone hole over Antarctica, with recovery expected by fifty years. But the unforeseen growth of aluminum oxides could cause ozone’s success to be suspended in the decades to come.

Among the 8,100 objects in low Earth orbit, 6,000 are Starlink satellites launched in recent years. The demand for global Internet coverage is driving a rapid acceleration in launches of small swarms of communications satellites. SpaceX is the leader in this endeavor, with permission to launch an additional 12,000 Starlink satellites and up to 42,000 planned. Amazon and other companies around the world are also planning constellations ranging from 3,000 to 13,000 satellites, according to the study authors.

Internet satellites in low Earth orbit have a short lifespan, about five years. Companies must then launch replacement satellites to maintain Internet service, continuing a cycle of planned obsolescence and unplanned pollution.

Aluminum oxides trigger chemical reactions that destroy stratospheric ozone, which protects the Earth from harmful UV rays. The oxides do not react chemically with ozone molecules, but trigger destructive reactions between ozone and chlorine that deplete the ozone layer. Because aluminum oxides are not consumed by these chemical reactions, they can continue to destroy molecule after molecule of ozone for decades as they drift through the stratosphere.

Yet little attention has been paid to the pollutants formed when satellites fall into the upper atmosphere and burn up. Previous studies of satellite pollution have largely focused on the consequences of propelling a launch vehicle into space, such as the release of rocket fuel. The new study, by a research team at the University of Southern California’s Viterbi School of Engineering, is the first realistic estimate of the extent of this long-lived pollution in the upper atmosphere, the researchers said. authors.

“It’s only in recent years that people have started to think this might become a problem,” said Joseph Wang, an astronautics researcher at the University of Southern California and corresponding author of the new study. “We were one of the first teams to examine what the implications of these facts might be.”

Sleeping threat

Because it is effectively impossible to collect data on a burning spacecraft, previous studies have used micrometeoroid analyzes to estimate potential pollution. But micrometeoroids contain very little aluminum, the metal that makes up 15 to 40 percent of the mass of most satellites, so these estimates do not apply well to new “swarm” satellites.

To get a more accurate picture of the pollution resulting from satellite re-entry, the researchers modeled the chemical composition and bonds within satellite materials as they interact at the molecular and atomic levels. The results allowed the researchers to understand how the material changes with different energy inputs.

By 2022, satellite re-entry increased the amount of aluminum in the atmosphere by 29.5% above natural levels, the researchers found. Modeling has shown that a typical 250 kilogram (550 pound) satellite, with 30% of its mass made up of aluminum, will generate about 30 kilograms (66 pounds) of aluminum oxide nanoparticles (size 1 to 100 nanometers) during its re-entry dive. Most of these particles are created in the mesosphere, between 50 and 85 kilometers (30 to 50 miles) above the Earth’s surface.

The team then calculated that, depending on particle size, it would take up to 30 years for aluminum oxides to drift to stratospheric altitudes, where 90% of Earth’s ozone is found.

The researchers estimated that by the time the currently planned satellite constellations are completed, each year, 912 tons of aluminum (1,005 US tons) will fall to Earth. This will release approximately 360 metric tons (397 US tons) of aluminum oxides per year into the atmosphere, a 646% increase over natural levels.