Researchers have unveiled an innovative methodology for monitoring the uncontrolled atmospheric descent of orbital detritus.
As these fragments pierce the atmosphere, they generate acoustic shocks, commonly known as sonic booms, which can be intercepted by terrestrial instrumentation primarily designed for geological surveillance—specifically, seismometers calibrated to detect the subterranean tremors of our geologically active planet.
This concept has moved beyond theoretical postulation; a collaborative effort by Johns Hopkins University planetary scientist Benjamin Fernando and Imperial College London engineer Constantinos Charalambous involved validating their hypothesis during the 2024 atmospheric reentry of the Shenzhou-15 orbital module.
The data acquired from seismic monitoring stations provided highly accurate measurements, delineating not only the reentry event itself but also its velocity, altitudinal strata, dimensions, angle of descent, and the precise moment of its disintegration during its fall.
“The observation of sequential, amplified disintegration offers profound insights into the mechanics of debris fragmentation. This has clear ramifications for enhancing our awareness of the space environment and for mitigating the hazards posed by orbital debris,” the investigators stated in their publication.
The proliferation of space junk represents a growing global concern. An April 2025 assessment by the European Space Agency indicates that approximately 1.2 million pieces of potentially hazardous orbital debris are currently present in Earth’s orbit, a figure projected to escalate as more satellites approach the conclusion of their service lives.
A non-operational spacecraft of this nature becomes impervious to communication or control. Should such an object collide with other debris or experience orbital decay sufficient for atmospheric reentry, humanity’s capacity is limited to observation.
However, Fernando and Charalambous posit that our observational capabilities are significantly more refined than previously assumed. Comprehending the trajectory, altitude, velocity, and fragmentation patterns of an object during atmospheric reentry can substantially improve our understanding of reentry dynamics and predict the likely impact zones.
A sonic boom is an acoustic phenomenon that occurs when an object traverses a medium at a velocity exceeding the local speed of sound. The term can be somewhat misleading, as it refers not to a single, distinct impulse but rather to a continuous wake or shock wave. This wave is formed by the compression of outward-propagating pressure waves into a conical shape trailing the high-speed object.
Objects entering Earth’s atmosphere from space frequently attain velocities that surpass the speed of sound, reaching supersonic and even hypersonic speeds. As they descend through the atmosphere, they generate a conical expanse of acoustic energy, perceived by observers in their path as a boom.
Seismic sensors are engineered for the detection of acoustic signals originating from deep within the Earth’s crust. Nonetheless, the researchers hypothesized that these sophisticated instruments could also be employed to track the acoustic Mach cone generated by descending space debris.
On April 2, 2024, the decommissioned Shenzhou-15 orbital module underwent atmospheric reentry over the southern California region. Measuring 2.2 meters (7.2 feet) and weighing 1.5 metric tons,its substantial size and mass presented a potential hazard to both aviation and terrestrial infrastructure, rendering it an ideal subject for this novel tracking methodology.
Accessing data from the publicly available Southern California Seismic Network and Nevada Seismic Network, the researchers sought evidence of the module’s passage. They identified signatures consistent with the reverberation of the Mach cone impacting the Earth’s surface, enabling them to reconstruct the object’s terminal flight path and disintegration.
According to the seismic analysis, the module was traveling at an estimated velocity of Mach 25 to 30, a finding that aligns with its pre-entry orbital parameters, which indicated a velocity of approximately 7.8 kilometers (4.8 miles) per second.
Furthermore, the investigators observed that while the initial phase of descent produced a singular, substantial sonic boom, this eventually resolved into a complex sequence of multiple, diminished sonic events. This observation is consistent with eyewitness accounts detailing the object’s fragmentation.
Although the module ultimately disintegrated harmlessly within the atmosphere, these findings definitively demonstrate that the characteristics of an atmospheric reentry trajectory can be accurately and precisely monitored by seismic networks. For objects that may not fully combust, this technique could potentially aid in identifying the most probable impact zone.
“Given that these objects inevitably reenter the atmosphere at supersonic velocities, should the largest fragments reach the ground, their impact will precede the detection of their associated sonic booms,” the researchers explained. “However, leveraging seismoacoustic methods for detection and tracking facilitates a more rapid and precise terrestrial localization of debris than would otherwise be attainable.”
An additional consideration involves the dispersal of potentially hazardous aerosol-sized particulates released during an object’s combustion and fragmentation. A thorough understanding of these failure processes could enable scientists to develop more accurate models for predicting the dispersion patterns and locations of these particulate clouds.
At present, uncontrolled reentries remain inherently unpredictable. While intervention may not be feasible, this new research illuminates a practical avenue for utilizing readily available tools to observe and comprehend the dynamics of such events.
