Researchers have found a new way to track debris falling from space, using earthquake sensors to monitor the sonic booms created as objects re-enter Earth’s atmosphere. This is a crucial development, given that roughly three large pieces of space junk crash to Earth daily, but current tracking methods are often inaccurate, especially as objects descend below 200 kilometers in altitude where atmospheric interactions become chaotic.
The limitations of existing radar and optical tracking became glaringly apparent during an incident in November 2022 when Spain and France partially shut down airspace due to a predicted crash of a Chinese rocket piece, which ultimately landed in the Pacific Ocean. This shutdown cost millions and highlighted how little we know about where debris actually lands.
The new method, developed by teams at Johns Hopkins University and Imperial College London, leverages the dense network of existing seismic sensors—originally designed to detect earthquakes—to reconstruct the paths of re-entering objects. Unlike sparse radar coverage, seismic sensors are widespread and their data is publicly available. The research team successfully used this approach to analyze the trajectory of a 1.5-ton module from China’s Shenzhou 17 capsule in April 2024.
Their findings were startling: the module traveled approximately 40 kilometers north of the U.S. Space Command’s prediction, potentially scattering debris between Bakersfield, California, and Las Vegas, Nevada. While no surface impacts were confirmed, the possibility underscores the real-world risk to the 50 million people living in that zone.
The primary benefit of this method isn’t prediction; it’s verification. The seismic data can pinpoint impact locations with far greater accuracy than current systems, allowing for faster retrieval of potentially hazardous fragments. This is especially important given past incidents like the 1978 Soviet satellite breakup over Canada, where radioactive debris was never fully recovered.
The ability to verify reentry events also challenges claims made by companies like SpaceX, which state that its Starlink satellites fully burn up upon re-entry. Experts doubt this, suggesting that durable materials like fuel tanks and batteries likely survive. Seismic tracking offers a means to confirm these claims, helping assess the true risks posed by falling debris to people, aircraft, and the environment.
Researchers are already looking to expand the method by incorporating acoustic sensors, which can detect sonic booms from thousands of miles away. This would be particularly valuable for tracking re-entries over the ocean, where radar and seismic data are scarce. The goal isn’t necessarily to stop debris from falling, but to understand how it falls, and to locate any surviving fragments with speed and precision.
“A supersonic object will always outrun its own sonic boom,” study lead author Benjamin Fernando explains. “You’re always going to see it before you hear it… If it’s going to hit the ground, there is nothing we can do about that. But we can try to reduce the time it takes to find fragments from days or weeks down to minutes or hours.”
