![Gamma-ray burst [GRB]. Credit: Cruz Dewilde/ NASA SWIFT.](https://nasaspacenews.com/wp-content/uploads/2025/05/gamma-ray-burst-credit-nasa-swift-cruz-dewilde-1-75x75.jpg)
Every year, Earth is bombarded by thousands of tons of space debris and natural meteoroids. Some of these fragments burn up harmlessly in the atmosphere, but others pose real threats to satellites, aircraft, and even life on the ground. The silent approach of space junk and meteoroids—traveling at tens of thousands of kilometers per hour—demands sophisticated tracking systems to predict their behavior. One unlikely but powerful tool has recently taken center stage: infrasound.
What Is Infrasound and Why Does It Matter?
Infrasound is sound that travels at frequencies below 20 Hz, too low to be heard by human ears. Yet this silent sound can travel thousands of kilometers through the atmosphere without losing strength. Nature uses infrasound to communicate powerful events: volcanic eruptions, earthquakes, and massive meteoroid explosions high in the sky.
Infrasound sensors—deployed around the globe by organizations like the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO)—are designed to pick up these sounds. Though originally created to detect nuclear blasts, these sensors are also perfect for capturing the rumbles of bolides—bright fireballs caused by large meteoroids breaking apart during atmospheric entry.
Because these sensors are constantly listening, scientists have years of data to work with, and it turns out we’ve been hearing space junk fall for decades—we just didn’t always know how to interpret the signals.
Tracking Space Junk and Meteoroids Using Sound
The moment an object enters Earth’s atmosphere, it starts interacting violently with air molecules. These interactions produce shock waves, and when a large enough object burns up, it creates a massive explosion—called a bolide—that can release the energy of several tons of TNT.
Elizabeth Silber’s research shows that these events generate long trails of infrasound as they streak across the sky. Unlike a single point explosion, a meteoroid’s path produces sound continuously—like a stretched-out sonic boom. This realization is crucial for understanding how to detect and locate these objects accurately.
Silber used global infrasound data to model how entry angles affect the signal. Her findings revealed that when objects enter the atmosphere at steep angles (greater than 60°), tracking them using infrasound is highly accurate. But when they come in more horizontally, or at shallow angles, the data becomes much harder to interpret.
Trajectory Matters: The Hidden Variable in Sound Detection
This trajectory issue is no small detail. When a meteoroid or piece of space junk enters at a low angle, it travels further through the atmosphere, generating sound along its path for a longer period. As a result, different infrasound stations may detect the event from different points along its trail, leading to confusion about its true origin and path.
Silber explained this by comparing a bolide to “a sonic boom stretched across the sky.” The sound isn’t from a single explosion—it’s a moving wave, and this movement creates complexity in how it’s interpreted.
Her work highlights a vital adjustment: when analyzing infrasound from meteoroids or debris, scientists must account for entry angle. Without this, predictions about where the object will land—or even where it came from—can be significantly off.
The Stakes Are Higher Than You Think
Why does any of this matter? Because space is getting crowded—and dangerous. Since the 1960s, satellites, rocket stages, tools dropped by astronauts, and defunct probes have filled Earth’s orbit with over 100 million pieces of debris, many of them too small to track but still large enough to cause serious damage.
Some of this debris eventually re-enters the atmosphere. Most burns up, but roughly 50 tons of space junk make it to Earth’s surface every year. Add that to natural meteoroids—some of which can explode with the power of small nuclear bombs—and the risk becomes clear.
Having reliable methods for detecting and tracking these events is critical for planetary defense, air traffic safety, and satellite protection. Infrasound can provide early alerts for incoming objects, giving space agencies and civil defense organizations time to act.
The CTBTO Network: A Global Listening System
One of the most powerful assets in this area is the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), which operates a global infrasound network designed to detect unauthorized nuclear tests. These same sensors also pick up data from meteoroids and re-entering space junk.
Silber leveraged this global system for her study, analyzing real-world bolide data to evaluate how well entry angle predictions matched actual signal behavior. The results confirmed that accurate detection is possible—but only if geometry is factored in.
In other words, to get the most out of infrasound detection, scientists must consider both what they hear and where it’s coming from—literally triangulating space events by tracking sonic ripples around the planet.
Combining Infrasound with Other Technologies
Infrasound is powerful, but it’s even better when combined with other tools. Optical telescopes, radar systems, satellite imaging, and infrared sensors all play roles in space object detection. But infrasound adds a unique advantage: it works day and night, through clouds and over long distances.
Combining these datasets can give a fuller picture. For example, if a satellite sees a bright flash and infrasound sensors hear the boom seconds later, we can correlate the visuals with the acoustic data to reconstruct the event. This is especially valuable in remote or oceanic areas where radar coverage is limited.
A New Frontier for Planetary Defense
What Silber’s work makes clear is that we’re entering a new age of space safety. Our planet is under constant threat—not from aliens, but from its own debris field and the cosmic rocks that zip by unannounced. Tracking these with greater precision helps mitigate disaster.
Already, agencies like NASA, ESA, and the United Nations Office for Outer Space Affairs (UNOOSA) are pushing for international collaboration on space junk monitoring. Incorporating infrasound data into global tracking systems could become a cornerstone of planetary defense in the 21st century.
Conclusion: The Future Sounds Promising
The universe may be silent in space, but the sky above Earth hums with signals—most of which we can’t hear. Thanks to scientists like Elizabeth Silber, we’re learning to listen in new ways. By tuning into infrasound, we can detect, trace, and prepare for space events that would otherwise go unnoticed until impact.
Reference:
Elizabeth Silber, Reducing uncertainties in bolide and space debris detection: The role of entry geometry in infrasound analysis (2025). DOI: 10.5194/egusphere-egu25-4030
