How Earthquake Detectors Track Space Junk

Thousands of pieces of abandoned spacecraft orbit Earth, and when gravity finally pulls them down, authorities rarely know exactly where they’ll land. Now researchers at Johns Hopkins University have demonstrated a clever solution. Surprisingly they have found using earthquake detecting seismometers they can track falling space debris in real time by listening for the sonic booms it produces. The technique successfully traced a Chinese spacecraft module as it streaked across California at Mach 25-30, revealing its actual trajectory lay 25 miles north of predictions, a significant improvement that could help authorities quickly locate potentially toxic debris and protect people from contamination.