Space junk falling out of orbit and crashing toward Earth is a growing threat. Old satellites and spacecraft parts reenter our planet’s atmosphere more than three times a day, reports BritPanorama.
When these objects burn through the atmosphere, they can release harmful substances. If they reach Earth’s surface, they pose risks of environmental contamination and potential collisions with buildings, infrastructure, or people.
However, tracking falling debris to mitigate its impact is complicated. Space junk can deorbit suddenly while traveling at speeds up to 18,000 miles per hour. Current monitoring methods that utilize radar and optical tracking struggle to accurately predict landing locations, particularly when debris breaks up during reentry. This shortage of precise location data often delays or prevents recovery efforts for toxic space residue.
Researchers from Johns Hopkins University and Imperial College London have developed a new technique to improve detection of space junk during reentry. Their approach employs seismometers—typically used to detect earthquakes—to identify the sonic booms generated by falling debris as it tumbles through the atmosphere.
The approach is grounded in the principle of detecting shock waves, similar to those produced by natural meteoroids or supersonic aircraft, which debris generates as it descends.
“We’ve known for a long time that space debris reentering the atmosphere produces sonic booms, exactly the same way as natural meteoroids or supersonic aircraft produce sonic booms,” said Benjamin Fernando, a postdoctoral research fellow at Johns Hopkins, who studies seismic activity on various planetary bodies.
Fernando, who co-authored a paper on the method, noted that during a NASA mission called InSight, similar techniques were explored by using meteoroids as seismic sources. The InSight lander, which landed on Mars in 2018, has recorded over 1,300 marsquakes caused by meteoroid impacts. This capability allowed scientists to “hear” the shock waves from meteoroids entering Mars’ atmosphere and pinpoint impact locations.
Applying these techniques to monitor space debris on Earth represents a significant advancement. Yet, Fernando acknowledged that space debris behaves differently from natural meteoroids, as it typically enters the atmosphere at shallower angles and can break apart more unpredictably, which results in increased risks.
A different prediction
The researchers tested their method using the uncontrolled reentry of China’s Shenzhou-15 spacecraft, a 2022 mission to the Tiangong space station. The spacecraft re-entered Earth’s atmosphere in April 2024 over California.
As the spacecraft burned up, it created sonic booms that registered on seismometers, which detected vibrations that did not resemble earthquakes. The study analyzed data from 125 instruments, with the intensity of these readings used to reconstruct the trajectory of the object in the atmosphere.
Compared with a projection by the US Space Force using radar data, the sonic booms method indicated the path was 25 miles (40 kilometers) further south. “There are no debris fragments that have been recovered,” Fernando stated, “so all we can say is that we see something that is different from the Space Force prediction.”
Further validation of the method is essential. “Our end goal is to produce a tool that we can integrate into a civil monitoring pipeline,” Fernando remarked. This tool could use open-source data to help locate falling objects, especially in urban areas like California or London, to support recovery operations.
The rapid detection of sonic booms would enable tracking of falling debris within moments of reentry, aiding in the identification of contamination sites. However, accurately estimating impact locations would take additional time to factor in elements such as wind conditions.
Fernando highlighted the historical significance of falling debris incidents, such as the 1978 reentry of the Soviet satellite Kosmos 954, which dispersed radioactive material over northern Canada, much of which remains unrecovered. He also referenced the early 2025 explosion of a SpaceX Starship rocket that scattered debris and heavy metals across marine environments and residential areas.
“Another thing that we’re becoming more aware of is that all of these reentries are beginning to change the composition of the atmosphere,” he added, stressing the serious implications of toxic chemicals potentially released during reentry.
An exciting new development
Hugh Lewis, a professor of astronautics at the University of Birmingham, emphasized that leveraging an existing network of seismic sensors makes the new approach “scalable, low-cost, and exciting.” He noted that this method aids understanding of the reentry process, which has historically been difficult to observe due to radar limitations.
Moriba Jah, a professor at the University of Texas at Austin, described this use of seismic networks as a demonstration of how “serendipitous” data can yield valuable insights into chaotic reentry events.
While the new method marks progress, Jah cautioned that reliance on strong shockwaves for detection may limit effectiveness, as smaller or disintegrating objects might not generate detectable signals. Furthermore, distinguishing reentry signals from those of other sources, such as aircraft or natural phenomena, presents a challenge. However, with careful validation alongside traditional tracking methods, this technique could serve as a complementary tool.
Davide Guzzetti, an associate professor of aerospace engineering, highlighted the importance of improved information gathering on reentering objects. This not only aids recovery efforts but can enhance our understanding of how space activities influence life on Earth.
“What I find especially fascinating is that these measurements may also provide insight into the fragmentation dynamics occurring during re-entry,” Guzzetti noted, suggesting potential for citizen-science projects that harness community involvement in debris tracking through sonic boom detection.
As the conversation around space debris evolves, scientific innovation is necessary to safeguard both the global environment and public safety.
