When internet-providing satellites — now being launched by the thousands — reach the end of their life, the byproducts of their fiery reentry into Earth’s atmosphere catalyze chemical reactions that destroy stratospheric ozone.

So while companies like SpaceX are launching thousands of small satellites into Low Earth Orbit (LEO) in the race to provide global internet coverage, this is creating a new problem. A new study published in the AGU journal Geophysical Research Letters suggests that in their attempt to connect the world, these satellites may also wreak havoc on the Earth’s ozone layer.

The Issue at Hand

When satellites reach the end of their operational life, they typically reenter Earth’s atmosphere and burn up. This process generates aluminum oxides, tiny particles that can catalyze (assist) chemical reactions. And these help to deplete the ozone layer, that important barrier that shields Earth from harmful ultraviolet (UV) radiation.

If you only have a few satellites, that’s not really a problem. But now, with more and more satellites in LEO, we could be in for a rude awakening. Just a handful of companies will be responsible for approximately 55,000 satellites, which could be enough to spell trouble for the ozone layer.

Of the 8,100 objects currently in LEO, 6,000 are Starlink satellites launched in the last few years. Demand for global internet coverage is driving a rapid ramp-up of launches of small communication satellite swarms. SpaceX is the frontrunner in this enterprise, with permission to launch another 12,000 Starlink satellites. And there are plans for as many as 42,000. Meanwhile, companies like Amazon are expected to launch another 3,000 to 13,000 satellites, and Chinese companies are expected to launch several tens of thousands.

The University of Southern California, Los Angeles study is the first to realistically estimate the extent of this long-lived pollution in the upper atmosphere. The research finds that aluminum oxides from reentering satellites have already increased eightfold between 2016 and 2022.

Environmental Impact

The researchers modeled the chemical reactions of satellite materials during reentry at molecular and atomic levels. They found that a typical 250-kilogram satellite can produce about 30 kilograms of aluminum oxide nanoparticles. The researchers estimated that by the time the currently planned satellite constellations are complete, 912 metric tons of aluminum will fall to Earth annually.

In 2022 alone, reentering satellites released 17 metric tons of aluminum oxide nanoparticles into the atmosphere. With the complete deployment of planned satellite constellations, this could increase to 360 metric tons per year — a staggering 646% increase over natural atmospheric levels.

Aluminum oxides don’t directly react with ozone but instead catalyze destructive reactions between ozone and chlorine. This leads to significant ozone depletion because aluminum oxides can continue these reactions for decades as they drift down through the stratosphere.

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

The study’s findings suggest that aluminum oxides produced by satellite reentry could delay the recovery of the ozone layer, which has been improving since the regulation of ozone-depleting substances under the 1987 Montreal Protocol. The ozone hole over Antarctica, expected to fully recover in about 50 years, might face new challenges due to the pollution from satellite reentry.

While previous studies have largely focused on pollutants from the launch phase, this research sheds light on satellites’ end-of-life environmental impacts. It underscores the need for the space industry to consider the full life cycle of satellites, including their disposal.

A Sustainable Alternative: The Wooden Satellite

In a bid to address the growing concerns of satellite pollution, Japan has come up with an innovative solution. Kyoto University and Sumitomo Forestry have developed the world’s first wooden satellite, set to launch on a SpaceX rocket from the Kennedy Space Center in September. This satellite, named LignoSat, represents a landmark step towards sustainable space technology.

Wood may seem unconventional for space technology, but it has several advantages. Unlike metal, wood does not leave harmful residues when it burns up upon reentry. Instead, it completely incinerates, reducing the risk of terrestrial pollution and debris. Additionally, wood is a sustainable resource and can withstand the harsh conditions of space without mass loss or decay.

Another significant benefit of wood is its transparency to many wavelengths, allowing for housing antennas within the frame. This eliminates the need for external antennas, simplifies satellite design, and reduces the risk of deployment failures.

The LignoSat project has been four years in the making. Several types of wood were tested, with magnolia wood ultimately chosen for its strength and durability. The satellite measures 10 cm (four inches) in all directions and will undergo rigorous testing at the International Space Station to ensure it can withstand the extreme temperature variations of space.

If successful, this could pave the way for more sustainable satellite designs, addressing the growing issue of space debris and pollution from reentering satellites.