New satellite images of the nuclear test site in North Korea shows an uptick in activity for the first time since the country's third nuclear test on February 12, stirring fears that a fourth test is imminent. The US-Korea Institute at Johns Hopkins University spotted the renewed activity on February 15 and just told the world about it on Wednesday. According to the AFP, however, the think tank "cautioned that there was not enough evidence to assert that a new test was in the works." It's certainly not evidence that a fourth test isn't in the works, either. In fact, it seems sort of imminent based on what we know about the North Korea's ambitions and the country's recent conversations with China. Three days ago, Pyongyang reportedly told Beijing that it's prepared for a fourth and even fifth nuclear test.

Who knows what the North Koreans are doing at that nuclear site. Maybe they're just cleaning up after the last test. Five kiloton nuclear bombs do make a heck of a mess, after all. Or maybe they're just stoking the fires of fear that the last test lit. Or maybe they are preparing for a fourth test. Wait, are we even sure that they did a third nuclear test? It's really hard to tell, because North Korea's gotten really really good at keeping its nuclear activities under a tight lid. Around the same time that the US-Korea Institute reported on the increased activity at the Punggye-ri site, news emerged that spy planes failed to discover nuclear-related particles that usually float up in the air after a blast.

This doesn't mean that there was not a nuclear explosion in North Korea last week — seismic activity and the opinions of pretty much every global expert on the subject indicates that there was. However, the North Koreans have done a very good job of concealing exactly what kind of nuclear bomb it was they detonated. Again, the 4.9-magnitude earthquake that followed the blast indicates that it was about five megatons in size, slightly smaller than the bomb the US dropped on Hiroshima. It's unclear if the fissile material was plutonium, as it was in the first two tests, or enriched uranium. If it's the latter, there could be trouble, since experts say that North Korea has the capacity to make almost unlimited quantities of the stuff.

The really scary thing is that we may never know. The nuclear facility is a labyrinth of tunnels that's filled with blockades — presumably to keep the capitalists out and the evidence in. "We need to remember that this is deep in the mountains [where] they tested that are formed of heavy rocks, not out in flat, exposed area," a South Korean official with knowledge of North Korea's test told Reuters. "We may not find anything." But hey, if there is a fourth blast, at least we'll feel it.