Thousands of satellites are due to burn up in the atmosphere every year – damaging the ozone layer and changing the climate

The world’s first artificial satellite, the Soviet Union’s Sputnik 1, was launched in October 1957. Just three months later, it fell out of orbit. As Sputnik hit the upper atmosphere at incredible speed, the friction would have caused it to heat up and almost entirely burn off. Some small remnants of the satellite would have remained in the upper atmosphere, like smoke and ash after a fire: humankind’s first space debris.

Seven decades on, scientists like us are only just beginning to piece together how this space debris might be damaging the ozone layer, the climate and even human health. We still don’t know how much of this debris the atmosphere can sustain before it causes significant environmental harm.

Today, the number of objects in orbit has surged to over 28,000. More than 11,000 of these are active satellites, with most belonging to commercial “mega-constellations”: groups of satellites that work together to deliver internet access. Examples include Starlink, operated by Elon Musk’s SpaceX, Amazon’s Kuiper or China’s Guowang.

Operators follow a 25-year rule: at this point, a satellite’s mission is deemed to have ended and it is lowered into the atmosphere where gravity and friction kicks in. While this helps clear space, it results in thousands of satellites burning up in the atmosphere each year.

A new problem

Until recently, the high-altitude destruction of satellites was not a concern. The amount of spacecraft debris was relatively small compared to debris from naturally occurring meteorites.

But by 2030, the global satellite population is expected to exceed 60,000, and thousands of spacecraft will be re-entering the atmosphere and burning up each year. With each satellite weighing as much as a small car, it all adds up. We are conducting research on the problem, and our early estimates are that around 3,500 tonnes of aerosols will be added to the atmosphere each year by 2033.

Aerosols are tiny particles suspended in the air. They can play an important role in Earth’s climate, either cooling or warming it depending on their type and colour. Light-coloured particles generally reflect incoming sunlight and cause cooling, while darker particles, usually containing soot, absorb sunlight and make the atmosphere warmer.

Some of these aerosols are particularly worrying. In 2023, US scientists discovered particles containing various metals, including aluminium and lithium, in the stratosphere. These particles originated from spacecraft and debris such as the disposable rocket boosters attached to them. When spacecraft burn up during re-entry, they release chemicals such as metal oxides and nitrogen oxides.

The full composition of these emissions remains unclear. But key pollutants found in satellite debris are known to affect the atmosphere’s thermal balance, potentially driving global climate change.

Aluminium oxide, for instance, could actually help cool the Earth by reflecting away sunlight. In fact, some geoengineering scientists have proposed injecting tiny particles of it into the stratosphere to keep global warming in check.

It’s way too early to say exactly how much cooling this will cause. And we don’t know how messing with Earth’s energy balance like this might trigger unintended consequences including extreme weather.

But we do know how the process works. And we know the amount of aluminium oxides from satellite re-entries is now approaching levels produced by meteorites – and will soon far exceed it. At a bare minimum, this is something we must track closely.

Reopening the ozone hole?

Aluminium oxide and other pollutants also act as catalysts in the breakdown of the ozone layer, a section of the stratosphere that shields the Earth from the Sun’s radiation.

In the 1970s and 1980s, the ozone layer was devastated by a group of chemicals known as CFCs that were widely used in fridges, spray cans and cleaning products. The 1987 Montreal protocol phased out CFCs and other ozone-depleting substances, and led to significant progress in reversing the damage.

According to the World Economic Forum, the economic benefits of protecting the ozone layer add up to around US$2.2 trillion (£1.7 trillion) in total. To take one example, a thinner ozone layer increases exposure to harmful ultra-violet (UV) radiation, leading to a higher incidence of skin cancer and cataracts.

The re-entry of satellites and space debris therefore may not only affect the Earth’s atmosphere but also pose serious risks to global climate and public health. More critically, unlike ground-based pollutants, pollutants from old spacecraft can persist in the upper atmosphere for decades or centuries, remaining undetected until their effects on ozone concentrations become evident.

New solutions required

History provides us with valuable lessons, allowing us to learn from past mistakes. Despite the success of the Montreal protocol, the ozone layer is not expected to fully recover until 2066, meaning it will take an 80-year effort to restore what was harmed in just a few decades.

The disaster of 21st-century climate change was set in motion when humankind began burning fossil fuels on a global scale in the mid-19th century. We are still working to resolve this problem by reducing carbon emissions. We must not add further environmental damage through satellite debris accumulating at the edge of Earth’s atmosphere.

There’s no simple solution, however. If we want the benefits of worldwide networks of satellites then we really do have to let them burn off in the atmosphere. It’s the only cost-effective disposal method at present.

For now, the space industry’s contribution to ozone depletion and climate change is relatively small. But, as space activity continues to grow exponentially, we cannot afford to overlook the consequences of satellite debris.

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Minkwan Kim receives funding from the UK Space Agency (UK Space Agency Contract No: UKSAG23A_00100), which is entitled as "Beyond the Burning: Researching and Implementing Policy Solutions for Sustainable Debris Ablation"

Ian Williams receives funding from EPSRC and AHRC.