Scientists have developed a method to monitor space debris reentering Earth's atmosphere using existing earthquake sensors. By detecting sonic booms from the debris, the technique provides precise tracking of its path and potential landing sites. This approach was tested on debris from China's Shenzhou-15 spacecraft.
Thousands of human-made objects orbit Earth, and as space debris falls back, it poses risks to people on the ground. A new study shows that networks of seismometers, originally designed to detect earthquakes, can track these reentries by capturing the shock waves they produce.
Lead author Benjamin Fernando, a postdoctoral research fellow at Johns Hopkins University who studies earthquakes on Earth, Mars, and other planets, highlighted the urgency. "Re-entries are happening more frequently. Last year, we had multiple satellites entering our atmosphere each day, and we don't have independent verification of where they entered, whether they broke up into pieces, if they burned up in the atmosphere, or if they made it to the ground," he said. "This is a growing problem, and it's going to keep getting worse."
The research, published on January 22 in the journal Science, tested the method on the reentry of the orbital module from China's Shenzhou-15 spacecraft on April 2, 2024. This object, about 3.5 feet wide and weighing more than 1.5 tons, was large enough to potentially endanger people.
Using data from 127 seismometers across southern California, Fernando and coauthor Constantinos Charalambous from Imperial College London calculated the module's speed at roughly Mach 25-30—about ten times the speed of the fastest jet aircraft. It moved northeast over Santa Barbara and Las Vegas, traveling 25 miles north of the path predicted by U.S. Space Command.
The seismic signals revealed the module's altitude and breakup point, aiding in understanding toxic particle dispersal from burning debris. Accurate tracking enables quicker recovery of hazardous materials, as seen in the 1996 Russian Mars 96 incident where a radioactive power source contaminated an area in Chile.
"In 1996, debris from the Russian Mars 96 spacecraft fell out of orbit... We'd benefit from having additional tracking tools, especially for those rare occasions when debris has radioactive material," Fernando noted.
This seismic approach complements radar-based predictions, which can be off by thousands of miles, by providing near real-time data on actual paths after atmospheric entry. "It's important that we develop as many methodologies for tracking and characterizing space debris as possible," Fernando emphasized.