North Korea’s latest underground nuclear weapons test Tuesday sends several messages to the international community, most of them unwelcome. For starters, this was the country’s third nuclear weapons demonstration and the first since Kim Jong-un took over in December 2011, indicating that Kim Jong-il’s successor has adopted his father’s confrontational approach to foreign relations.

In addition, the detonation—about 380 kilometers northeast of Pyongyang—touched off a seismic event measuring between magnitude 4.9 and 5.2, which corresponds to a weapon with an estimated explosive yield of six or seven kilotons, according to South Korea’s Defense Ministry, as reported by the Associated Press. The explosion surpasses the yield of North Korea’s 2009 nuclear test (estimated to have been between two and six kilotons) and a one-kiloton test in 2006.

Despite several United Nations Security Council resolutions to prevent North Korea from testing nuclear explosions or missiles, the country in December launched a rocket that put the country’s first satellite into orbit. This followed a failed rocket launch in April 2012. The takeaway is that the North is developing not just a nuclear warhead but the means to deliver it great distances as well.

For its part, North Korea accuses South Korea, backed by the U.S., of stepping up the “development and deployment of ballistic missiles with a firing range of 800 kilometers, capable of striking the entire region of the DPRK [Democratic People’s Republic of Korea, aka the North] as well as the deployment of Aegis destroyer's ship-to-ground cruise missile with a firing range of 500 kilometers and a long-range air-to-ground missile for fighters,” according to the Korea News Service. Aegis is a combat system developed by Lockheed Martin and deployed by South Korea’s navy on some of its ships.

Scientific American touched base with Frank von Hippel, a professor at Princeton University's Woodrow Wilson School of Public and International Affairs and co-founder of the school's Program on Science and Global Security, about this latest turn of events in North Korea’s quest to become a nuclear power.

[An edited transcript of the interview follows.]

What does North Korea’s latest nuclear test (including the seismic activity that gave it away) tell us about their nuclear capabilities and objectives? For example, could we tell from a distance whether North Korea has switched from plutonium to uranium as a source of fuel for it weapons?
That we will only be able to tell if gaseous fission products leak out of the mountain and are picked up by U.S. and South Korean aircraft off shore or by land stations.

As dismal as this may seem, are these tests the best way for the rest of world to determine what North Korea is capable of, and how far it’s willing to go?
I think that they are trying to communicate that they have a ballistic missile–deliverable nuclear warhead with a Hiroshima-scale yield. That seems increasingly plausible.

What message is North Korea sending to South Korea, the U.S., China and other countries concerned about its deployment of nuclear weapons?
What they appear to want is respect and outside economic help that does not undermine the regime.

What repercussions can North Korea expect following this latest incident, and what more can be done to deter future tests?
I don't know. I used to think that a deal was possible that would persuade them to give up their nuclear weapon option but, now that they have it, it appears that they want to keep it and have the rest of the world accept that.

What does North Korea stand to gain by becoming a "nuclear power" and enduring additional sanctions imposed by the U.S. and other countries?
I don't think that they have much to gain beyond having a deterrent [against any attack]. But the fear is that they will export nuclear-weapons materials or technology, so we can't ignore them either.

(For a more in-depth discussion of North Korea’s nuclear ambitions with von Hippel, a former assistant director for national security in the White House Office of Science and Technology during the Clinton administration, see our December 20, 2011, Ask the Experts, “North Korea’s Nukes: Does the Death of Kim Jong-il Mean Trouble for the U.S.?”)