As space junk increasingly reenters Earth’s atmosphere, scientists are turning to infrasound—low-frequency sound waves—to track these objects and predict their impact zones, enhancing planetary defense and public safety.
Key Points at a Glance
- Approximately 50 tons of space debris fall to Earth annually, posing risks to populated areas.
- Infrasound sensors detect low-frequency sounds from meteoroids and reentering space junk.
- Trajectory angle affects the accuracy of infrasound-based tracking methods.
- Research presented at EGU25 highlights the need for improved tracking of space debris.
With humanity’s ambitions reaching ever further into orbit, a silent problem is accumulating above our heads: space debris. Broken satellites, spent rocket stages, and fragmented components from past missions now orbit Earth in ever-growing numbers. While many pieces remain in orbit for years, gravity and atmospheric drag inevitably pull some of them back down. Around 50 tons of this debris reenters our atmosphere every year, and although most burns up, an increasing number of fragments survive and fall to Earth—sometimes near populated areas.
Tracking these falling objects has long been a challenge. Unlike meteoroids, which arrive from space at predictable speeds and trajectories, space junk often tumbles irregularly and reenters unpredictably. This unpredictability presents a real concern for public safety. That’s why scientists are now turning to an unexpected tool: sound.
More precisely, infrasound—sound waves below the range of human hearing—is proving to be a game changer in monitoring objects as they plunge through the atmosphere. These waves, generated by explosive events like meteoroid airbursts or space debris reentry, can travel thousands of kilometers through the air, reaching specially designed sensors far from the original source.
At the recent European Geosciences Union (EGU) General Assembly 2025, Dr. Elizabeth Silber of Sandia National Laboratories presented her team’s work on using infrasound to monitor and reconstruct the trajectories of reentering space objects. Her study used data collected from the Comprehensive Nuclear-Test-Ban Treaty Organization’s global network of infrasound stations—originally designed to detect nuclear detonations.
Silber’s analysis focused on how the angle of entry affects the accuracy of infrasound detection. Objects entering Earth’s atmosphere at steep angles—more than 60 degrees—generate cleaner, more distinct infrasound signatures. These signatures can be traced with greater confidence, enabling scientists to reconstruct the object’s path and predict impact locations with improved precision.
In contrast, shallow entries—those arriving at angles less than 30 degrees—pose a much bigger challenge. They create more diffuse infrasound signals, influenced by atmospheric drag and turbulence. The result is a more complex acoustic footprint, which can confuse detection algorithms and reduce tracking accuracy.
Despite these difficulties, the value of infrasound-based monitoring is clear. It offers an independent, physics-based method of verifying reentry events, especially in regions lacking radar or optical tracking capabilities. Moreover, it complements existing space situational awareness systems, offering an added layer of global coverage.
Beyond safety, this capability also serves diplomatic and scientific goals. In the case of unknown reentry events, especially those with visible fireballs or sonic booms, infrasound can help distinguish between natural meteoroids and human-made debris. This clarity can be critical in avoiding confusion or alarm, especially in sensitive geopolitical contexts.
The ability to accurately track space debris also has ramifications for legal responsibility and liability. International space law assigns responsibility for damage caused by space objects to the launching state. Being able to determine exactly where and when an object reenters—and whether it causes damage on the ground—could play a critical role in future disputes and claims.
Looking ahead, Silber and her colleagues emphasize the need for more integrated approaches. They suggest combining infrasound data with satellite observations, ground-based radar, and atmospheric modeling to build a comprehensive early warning system. Such a system could issue alerts when large debris objects are expected to reenter near populated areas, allowing for timely evacuations or mitigation measures.
Infrasound is also gaining ground as a tool for monitoring other atmospheric phenomena. From volcanic eruptions to supersonic aircraft and large explosions, its applications are diverse. But in the context of orbital debris, it may become one of the most vital methods in our toolkit.
With space traffic growing rapidly—thanks to mega-constellations of satellites, commercial space launches, and increasing exploration missions—the likelihood of hazardous reentries will only rise. By listening to the low rumbles from the sky, scientists hope to better predict when and where space junk will return to Earth—and how to protect people when it does.
Source: European Geosciences Union
