‘Megaconstellations’ of satellites could endanger ozone hole recovery

Satellites burning up in the atmosphere are leaving behind particles of aluminium oxide that are damaging the ozone layer, a situation predicted to worsen as more low-Earth-orbit satellites launch.

Illustration of multiple satellites in orbit
Illustration of multiple satellites in orbit - AdobeStock

The 1987 Montreal Protocol successfully regulated ozone-damaging chlorofluorocarbons (CFCs) to protect the ozone layer, shrinking the ozone hole over Antarctica with recovery then expected in the next fifty years.

However, new research from the University of Southern California Viterbi School of Engineering has shown that these oxides have increased eight-fold between 2016 and 2022 and will continue to accumulate as the number of low-Earth-orbit (LEO) satellites increase, jeopardising the ozone layer in decades to come.

The researchers outlined that, of the 8,100 objects in LEO, 6,000 are Starlink satellites launched in the last few years, and that the demand for global internet coverage is driving a rapid ramp up of launches of small communication satellite swarms.

SpaceX is the front runner in this enterprise, with permission to launch another 12,000 Starlink satellites and as many as 42,000 planned. Amazon and other companies around the globe are also planning constellations ranging from 3,000 to 13,000 satellites, the authors of the study added.

As internet satellites only have an operational lifespan of around five years, companies have to launch replacement satellites to maintain internet service, which continues a cycle of planned obsolescence and unplanned pollution, the researchers said.

Aluminium oxides trigger chemical reactions that destroy stratospheric ozone, which protects Earth from UV radiation. The oxides do not react chemically with ozone molecules, instead triggering destructive reactions between ozone and chlorine that deplete the ozone layer.

The researchers said that because aluminium oxides are not consumed by these chemical reactions, they can continue to destroy molecule after molecule of ozone for decades as they drift down through the stratosphere.

“Only in recent years have people started to think this might become a problem,” Joseph Wang, a researcher in astronautics at the University of Southern California and corresponding author of the study, said in a statement. “We were one of the first teams to look at what the implication of these facts might be.”

As it is effectively impossible to collect data from burning spacecraft, previous studies used analyses of micrometeoroids to estimate potential pollution. However, the researchers said that micrometeoroids contain very little aluminium, the metal that makes up 15 – 40 per cent of the mass of most satellites, so these estimates did not apply well to new ‘swarm’ satellites.

Instead, the researchers modelled the chemical composition of and bonds within satellites’ materials as they interact at molecular and atomic levels. The results gave the researchers an understanding of how the material changes with different energy inputs.

The study, funded by NASA, found that in 2022, re-entering satellites increased aluminium in the atmosphere by 29.5 per cent over natural levels.

The modelling showed that a typical 250kg satellite with 30 per cent of its mass being aluminium will generate about 30kg of aluminium oxide nanoparticles (1-100nm in size) during re-entry. Most of these particles are created in the mesosphere, 50-85km (30-50 miles) above Earth’s surface.

The team then calculated that, based on particle size, it would take up to 30 years for the aluminium oxides to drift down to stratospheric altitudes, where 90 per cent of Earth’s ozone is located.

The researchers estimated that by the time the currently planned satellite constellations are complete, every year, 912 metric tons of aluminium will fall to Earth. That will release around 360 metric tons of aluminium oxides per year to the atmosphere, an increase of 646 per cent over natural levels.

The study, published in the open-access AGU journal Geophysical Research Letters, can be read in full here.