In the days and weeks ahead, nuclear experts will be hunting for airborne radioactive particles that could shed light onNorth Korea's assertion that it tested a hydrogen bomb, but drawing an independent conclusion could prove lengthy and difficult.
Seismic monitoring stations operated by governments around the world detected an earthquake on Wednesday morning that the U.S. Geological Survey measured at a magnitude of 5.1.
The location of the quake, near a known North Korean nuclear test site, and its seismic characteristics led experts to quickly conclude that North Korea had probably conducted a fourth nuclear test. Pyongyang then announced it had done so.
But it is the detection of airborne radioactive particles that will give clues as to the type of device that was set off and whether it was a hydrogen bomb, which is more powerful than an atomic bomb and would mark a technological advance for North Korea.
Another possibility is that it was not a nuclear device at all but a conventional high-yield explosive.
Following the North's last nuclear test, in 2013, it was 55 days before radioactive xenon gas was detected at a monitoring station in Japan, located about 1,000 km (600 miles) from the test site, which pointed to a nuclear blast by Pyongyang.