Thousands of satellites are deployed in “mega-constellations” to meet the growing need for internet services worldwide, with many more planned for launch soon. However, these compact satellites have short service lives and are known to emit pollutants that can damage the ozone layer when they break up on re-entry. A recent study published in Geophysical Research Letters has for the first time quantified the extent of this contamination. Credit: SpaceX/public domain
When internet-providing satellites—now launched by the thousands—reach the end of their useful lives, the remnants of their burn-up in Earth’s atmosphere will begin chemical reactions that destroy stratospheric ozone.
When aging satellites re-enter Earth’s atmosphere and break up, they release tiny particles of aluminum oxide that eat away at Earth’s ozone layer. A recent study revealed that the presence of these particles increased eightfold from 2016 to 2022 and is expected to continue to increase with the increasing number of satellites in low Earth orbit.
The 1987 Montreal Protocol successfully regulated ozone-depleting CFCs to protect the ozone layer, shrinking the ozone hole over Antarctica with recovery expected over the next fifty years. However, an unexpected increase in aluminum oxides could disrupt the progress made in ozone restoration in the coming decades.
Of the 8,100 objects in low Earth orbit, 6,000 are Starlink satellites launched in the past few years. The demand for global Internet coverage is leading to a rapid increase in the launch of small communications satellite swarms. SpaceX is the leader in this venture, with 12,000 more Starlink satellites authorized to launch 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, the study authors said.
Internet satellites in low Earth orbit are short-lived, about five years. Companies must then launch replacement satellites to maintain Internet service, perpetuating a cycle of planned obsolescence and unplanned pollution.
Aluminum oxides cause chemical reactions that destroy stratospheric ozone, which protects the Earth from harmful ultraviolet radiation. The oxides do not chemically react with ozone molecules, instead causing destructive reactions between ozone and chlorine that destroy the ozone layer. Because aluminum oxides are not consumed by these chemical reactions, they can continue to destroy ozone molecule by molecule for decades as they drift down through the stratosphere.
Yet little attention has yet been paid to the pollutants produced when satellites fall into the upper atmosphere and burn up. Earlier studies of satellite pollution largely focused on the consequences of launching a launch vehicle into space, such as the release of rocket fuel. The new study, conducted 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-lasting pollution in the upper atmosphere, the authors said.
“It’s only in recent years that people have started to think that 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 look at what the significance of these facts might be.”
The study was published in the open access journal AGU Geophysical Research Letterswhich publishes high-impact reports in short format with immediate implications spanning all Earth and space sciences.
A dormant threat
Because it is virtually impossible to collect data from a burning spacecraft, previous studies have used analyzes of micrometeoroids to assess potential contamination. But micrometeoroids contain very little aluminum, the metal that makes up 15% to 40% of the mass of most satellites, so these estimates don’t apply well to new “swarm” satellites.
To get a more accurate picture of satellite re-entry contamination, the researchers modeled the chemical composition and bonds in the satellites’ materials as they interacted at the molecular and atomic level. The results gave the researchers insight into how the material changes with different energy inputs.
In 2022, satellite re-entry increased aluminum in the atmosphere by 29.5% over natural levels, the researchers found. Modeling showed that a typical 250-kilogram (550-pound) satellite, with 30% of its mass being aluminum, would generate about 30 kilograms (66 pounds) of aluminum oxide nanoparticles (1-100 nanometers in size) during its re-dipping. Most of these particles are created in the mesosphere, 50-85 kilometers (30-50 miles) above the Earth’s surface.
The team then calculated that, based on particle size, it would take up to 30 years for the aluminum oxides to descend to stratospheric heights, where 90% of Earth’s ozone is found.
The researchers estimated that by the time the currently planned satellite constellations are complete, 912 metric tons of aluminum (1,005 US tons) will fall to Earth each year. This would release about 360 metric tons (397 US tons) of aluminum oxides annually into the atmosphere, a 646% increase over natural levels.
Reference: “Potential ozone depletion from satellite extinction during atmospheric re-entry in the mega-constellation era” by Jose P. Ferreira, Ziyu Huang, Ken-ichi Nomura, and Joseph Wang, 11 Jun 2024, Geophysical Research Letters.
DOI: 10.1029/2024GL109280
This work was funded by NASA.
