New way to track deadly space junk falling to Earth developed

By Stephen Beech

A way of accurately tracking potentially deadly space junk as it falls to Earth has been devised.

Seismometers usually used to detect earthquake activity can pinpoint sounds of space debris entering the atmosphere, say scientists.

Space debris - the thousands of pieces of human-made objects abandoned in Earth’s orbit - pose a potentially catastrophic threat to life when they enter the atmosphere at high speed.

To locate possible crash sites, scientists have devised a way to track falling debris using existing networks of earthquake-detecting seismometers.

They say the new tracking method, described in the journal Science, generates more detailed information in near real-time than authorities have today.

That information will help to quickly locate and retrieve the charred and sometimes toxic remains, according to the research team.

Study lead author Dr. Benjamin Fernando, of Johns Hopkins University, Baltimore, said: “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.

“This is a growing problem, and it’s going to keep getting worse.”

Dr. Fernando and colleague Dr. Constantinos Charalambous, a research fellow at Imperial College London, used seismometer data to reconstruct the path of debris from China’s Shenzhou-15 spacecraft after the orbital module entered the Earth’s atmosphere on April 2, 2024.

Measuring around 3.5 feet wide and weighing more than 1.5 tons, the module was large enough to potentially pose a threat to life.

Dr. Fernando said: "Space debris entering the Earth’s atmosphere moves faster than the speed of sound and, consequently, produces sonic booms, or shock waves, similar to those produced by fighter jets.

"As the debris streaks toward the Earth, vibrations from the shockwave trail behind, rumbling the ground and pinging seismometers along the way."

He says mapping out the activated seismometers allows researchers to follow the debris’ trajectory, determine which direction it’s moving, and estimate where it may have landed.

By analysing data from 127 seismometers in southern California, the research team calculated the path and speed of the module.

Cruising at Mach 25-30, the module streaked through the atmosphere traveling north-east over Santa Barbara and Las Vegas at around 10 times the speed of the fastest jet in the world.

The researchers used the intensity of the seismic readings to calculate the module’s altitude and pinpoint how it broke into fragments.

They then used trajectory, speed, and altitude calculations to estimate the module was traveling around 25 miles north of the trajectory predicted by U.S. Space Command based on measurements of its orbit.

Dr. Fernando said: "Engulfed in flames, falling debris sometimes produces toxic particulates that can linger in the atmosphere for hours and waft to new parts of the planet as weather patterns change.

"Knowing the trajectory of the debris will help organisations track where those particulates go and who might be at risk of exposure.

"Near-real time tracking will also help authorities quickly retrieve objects that make it to the ground."

He says rapid retrieval is especially important because debris can carry harmful substances.

Dr. Fernando said: “In 1996, debris from the Russian Mars 96 spacecraft fell out of orbit.

"People thought it burned up, and its radioactive power source landed intact in the ocean.

"People tried to track it at the time, but its location was never confirmed.

“More recently, a group of scientists found artificial plutonium in a glacier in Chile that they believe is evidence the power source burst open during the descent and contaminated the area.

"We’d benefit from having additional tracking tools, especially for those rare occasions when debris has radioactive material.”

Scientists had to previously rely on radar data to follow an object decaying in low Earth orbit and predict where it would enter the atmosphere.

But the researchers say re-entry predictions can be off by thousands of miles in the worst cases.

But seismic data can complement radar data by tracking an object after it enters the atmosphere, providing a measurement of the actual trajectory.

Dr. Fernando said: “If you want to help, it matters whether you figure out where it has fallen quickly - in 100 seconds rather than 100 days, for example."

He added: “It’s important that we develop as many methodologies for tracking and characterising space debris as possible.”