As the number of space launches soars, so does the threat from falling space junk. Now, earthquake technology is getting a new gig: tracking dangerous debris as it comes crashing back to Earth. In a study published this week in Science, researchers from Johns Hopkins University and Imperial College London demonstrated that networks of seismometers—the same ones that listen for earthquakes—can also detect the sonic booms produced by plummeting spacecraft.
The test case? China’s 3,300-pound Shenzhou-15 orbital module, which reentered the atmosphere over Southern California on April 2, 2024. The module, abandoned since it separated from a crew capsule returning three Chinese astronauts from the Tiangong space station in 2023, generated powerful sonic booms as it tore through the sky at supersonic speeds.
By analyzing data from more than 120 seismometers, scientists mapped the debris’ path with surprising accuracy. The sensors picked up the shockwaves—vibrations in the ground that, while similar to earthquake tremors, had a telltale signature. The result? The mapped trajectory landed nearly 20 miles (30 kilometers) farther south than radar had predicted, with some sources putting the difference at 25 miles (40 kilometers). For recovery teams, that’s a major advantage, especially if the debris contains hazardous material.
Sonic Booms Offer New Eyes on the Sky
The method isn’t just about pinpointing where debris lands. Within minutes or even seconds, these seismic readings can reveal the speed, direction, and fragmentation of an incoming object. In remote regions—like the South Pacific, where nuclear blast monitoring stations are already set up—similar techniques could further sharpen our ability to track and recover space junk.
But, as promising as this sounds, it’s not a silver bullet. The approach works best for large, fast-moving objects that break up low enough to send strong shockwaves into the ground. “Many reentering objects are too small or disintegrate too high in the atmosphere to produce signals like this at all,” noted one outside expert, cautioning that the system won’t catch most debris and isn’t a standalone solution.
Still, with more launches—and more junk—expected in coming years, treating sonic boom tracking as a “big data” problem could be a smart move. Researchers envision leveraging existing seismic networks on the U.S. West Coast and building new ones in global hotspots. It’s a striking example of how tools built for earthquakes might help us dodge a very different kind of disaster from above.
