Scientists warn of emissions risks amid rising boom for satellites

Scientists are raising growing alarms about a lesser-known consequence of the rapidly expanding space industry: atmospheric pollution caused by rocket launches and by satellites and rocket stages burning up during reentry. With hundreds of satellites launched every year and tens of thousands more planned, orbital activity has accelerated dramatically. 

SpaceX remains the undisputed leader, with its Starlink mega-constellation now exceeding 9,000 satellites. But the space economy extends well beyond the United States, encompassing military, scientific, and commercial missions launched by Europe, China, Russia, India, Israel, Japan, and South Korea. In 2025, the global number of orbital launches reached 300 for the first time, and experts say the total is likely to continue climbing.

Until recently, much of the scientific concern around this surge focused on risks such as orbital debris interfering with astronomical observations, collisions in space, or fragments falling back to Earth. Now, researchers are increasingly focused on two additional threats: emissions produced during rocket launches and the pollutants released when satellites and rocket stages burn up on reentry.

“Both of these processes are producing pollutants that are being injected into just about every layer of the atmosphere,” said Eloise Marais, an atmospheric scientist at University College London who tracks emissions from launches and reentries, as cited by the Yale School of Environment.

Commercial satellite systems such as Starlink are designed with relatively short operational lifespans—typically around five years—after which satellites are deliberately deorbited and replaced. This creates a continuous cycle of launch, deployment, deorbit, and destruction. Scientists warn that this cycle effectively turns Earth’s upper atmosphere into a disposal site for space hardware.

As Jonathan MacDowell, a scientist at Harvard University and the Smithsonian who has tracked space launches for decades, put it: “We are now in this regime where we are doing something new to the atmosphere that hasn’t been done before.” He and other researchers stress that the cumulative effects of frequent launches and reentries remain poorly understood, leaving uncertainty about potential consequences for weather, climate, and human health.

Particular concern surrounds what happens when satellites and rocket stages burn up during reentry. The space industry often lacks precise knowledge of the full material composition of the equipment that disintegrates in the atmosphere. However, scientists using high-altitude air sampling have identified a wide range of vaporized elements in the mesosphere during deorbits.

A recent study published in the Proceedings of the National Academy of Sciences (PNAS) found that these materials “condense into aerosol particles that descend into the stratosphere.” The particles contained aluminum, silicon, copper, lead, lithium, and rarer elements such as niobium.

As the Yale article warns, the presence of aluminum is especially troubling. Its combustion forms aluminum oxide nanoparticles, which scientists say could damage the ozone layer and undermine decades of progress made since the phase-out of chlorofluorocarbons.

A study in Geophysical Research Letters estimated that the ablation of a single 250 kilograms satellite could generate around 30 kilograms of aluminum oxide nanoparticles. Newer Starlink satellites are significantly heavier—about 810 kilograms—raising concerns about even greater pollution. These particles may remain suspended in the atmosphere for decades.

Researchers now believe the impact of satellite reentries may exceed that of natural meteoroids, which also burn up in the atmosphere.

“You might have more mass from the meteoroids,” said Aaron Boley, an astronomer at the University of British Columbia, but “these satellites can still have a huge effect because they’re so vastly different [in composition].”

According to the article, launch emissions present another challenge. While carbon dioxide emissions from rockets remain small compared with those from commercial aviation, scientists say rocket plumes injected directly into the stratosphere during liftoff may have outsized effects on ozone depletion. Most rockets currently use RP-1, a highly refined kerosene burned with liquid oxygen. This process releases black carbon particles that absorb solar radiation.

A modelling study led by Christopher Maloney of the University of Colorado found that, under projected industry growth, black carbon emissions could raise stratospheric temperatures by up to 1.5 degrees Celsius, leading to significant ozone losses in the Northern Hemisphere.

Some researchers warn that unchecked space pollution could become the atmospheric equivalent of plastic waste in the oceans. Others argue there is still time to mitigate the risks, noting that the commercial space sector is relatively young and that regulatory and technological solutions could still be developed before irreversible damage occurs.

By Nazrin Sadigova