DARPA accidentally detects SpaceX Falcon 9 rocket reentry by listening to Earth's atmosphere

Researchers with the U.S. military's Defense Advanced Research Projects Agency (DARPA) have successfully used Earth's atmosphere as a sensor to detect a distant disturbance.DARPA's AtmoSense program aims to study how sound waves or electromagnetic frequencies travel through Earth's atmosphere, and to find ways to use these waves as a "global sensor" to detect and pinpoint disturbances such as earthquakes or volcanic eruptions.But researchers with the AtmoSense program found that, when studying waves created by controlled explosions in New Mexico, they were also able to detect atmospheric disturbances created by a Space Falcon 9 rocket reentry. "The phenomenon is highly repeatable," said Michael Nayak, AtmoSense program manager, in a DARPA statement. "We discovered an unplanned new technique for identifying objects entering the earth's atmosphere."Nayak explained that the technique works by measuring flows of electrons in the atmosphere, comparing them to water streaming from a hose."Th...