The effects of satellite reentry into the atmosphere go far beyond the visual spectacle we see in the sky—that glowing trail that resembles a meteor. Behind the beauty lies a rarely discussed physical and environmental process. What really happens to these objects as they burn up in the atmosphere? Do they vanish completely, or do they leave an invisible trace in the air? In this article, we’ll explore what goes on behind the scenes of this phenomenon and reflect on its often-overlooked consequences for Earth.
What Is a Satellite Reentry?
When an artificial satellite or part of a rocket completes its mission in space, it must take one final step: returning to Earth. This return is known as atmospheric reentry and can be either controlled or uncontrolled.
A controlled reentry happens when space agencies plan the object’s fall, usually directing it to a remote region of the ocean known as Point Nemo—the most isolated spot on the planet. On the other hand, uncontrolled reentry occurs when there’s no more command over the object, and it follows a natural descent path, influenced by factors such as gravity, atmospheric drag, and Earth’s rotation.
In both cases, the phenomenon is visually striking: the object enters the atmosphere at speeds exceeding 25,000 km/h, creating friction with the air and intense heat, enough to cause its fragmentation and partial or complete incineration. From the ground, this appears as a luminous trail streaking across the sky—often mistaken for a meteor.
Recently, in May 2025, one such reentry was widely recorded in Brazil: the second stage of a Falcon 9 rocket from SpaceX, originally launched in 2014. The object passed over regions like the Federal District, Goiás, Bahia, and Minas Gerais, drawing attention for the beauty of the trail it left in the sky. However, few realized that this beauty conceals the effects of satellite reentry into the atmosphere—and that’s exactly what the rest of this article aims to explore.
What Happens to a Satellite During Reentry?
During reentry, the satellite is subjected to extreme conditions. Contact with the atmosphere at high speed causes intense heating due to friction and compression of air molecules. Temperatures can exceed 3,000°C, causing materials to melt, vaporize, or fragment.
The most common satellite components—aluminum, titanium, lithium, plastics, ceramics, and electronic circuits—transform into gases, metallic vapors, or aerosols. In many cases, no recognizable parts remain. But that doesn’t mean the object has ceased to exist. It has merely changed form.
Most small satellites are fully disintegrated before reaching the ground. However, larger objects or those with more resistant parts, like titanium fuel tanks, can survive reentry and fall into remote areas of Earth or the ocean.
Do Satellites Truly Disappear? The Entropy Perspective
The idea that a satellite “disappears” in the atmosphere is physically inaccurate. After all, according to the second law of thermodynamics, energy and matter are not lost; they simply transform, increasing the system’s entropy.
In practice, this means the satellite doesn’t vanish: it becomes heat, gases, metallic vapors, and microscopic particles. These residues, in turn, spread through the atmosphere and, in some cases, remain suspended for weeks or even years, depending on their altitude and composition.
In other words, the object that amazed observers by falling like an “artificial comet” is still with us. It’s just now invisible and dispersed.
Satellite Reentry into the Atmosphere and Its Effects: Gases and Metals in the Air
Recent research has shown that frequent satellite reentries are releasing significant amounts of metals into the upper atmosphere. Additionally, a study published in Geophysical Research Letters showed a nearly 30% increase in aluminum concentration in certain atmospheric layers—directly linked to reentries.
These materials include:
Aluminum oxides: from structural components and panels
Lithium and copper vapors: from batteries and circuits
Burned plastic residues: which can produce volatile organic compounds
Despite their wide dispersion, these elements have the potential to interfere with atmospheric processes such as cloud formation, radiation propagation, and even ozone chemistry. While there’s still no scientific consensus on the long-term impacts, the warning signs are already there.
A Growing Concern: The Megaconstellation Era
With the race to launch satellite megaconstellations like Starlink (SpaceX) and OneWeb, tens of thousands of satellites are expected to enter orbit in the coming years. At the end of each operational cycle, these structures must reenter the atmosphere.
If today we already worry about a few thousand objects, what can we expect when that number multiplies by ten? Even if each individual reentry releases only small amounts of materials, the cumulative effect could become globally significant.
Some scientists compare it to what happened with microplastics in the oceans: initially seen as negligible, they’re now found everywhere—even inside our bodies.
Are We Polluting the Sky Without Realizing It?
The image of a satellite burning across the sky can be mesmerizing. However, behind the spectacle lies a transformation process that is far from neutral. What today looks like a streak of light may become, in the future, part of a global environmental debate.
Understanding what happens to these objects is the first step toward rethinking how we want to occupy space. Space exploration doesn’t need to repeat the mistakes of industrial history. But for that, we must look up with the same level of responsibility we demand from what happens around us.
Sources and Referenced Studies
- Geophysical Research Letters. Satellite reentries increase aluminum in the atmosphere
- University of Southampton. Environmental impact of deorbited satellites
- European Space Agency (ESA). Workshop on Atmospheric Re-entries
- PEER.org. Satellite-generated atmospheric pollution to skyrocket
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