This image was taken Jan. 30 by astronauts aboard the International Space Station. North Korea is the large dark patch in the middle. The only significant light is from its capital, Pyongyang. The next photo adds reference points. NASA.gov hide caption

itoggle caption NASA.gov

South Korean Park Yang-gon (left) and his North Korean brother Park Yang Soo get emotional as they meet Thursday during the Separated Family Reunion Meeting at Diamond Mountain resort in North Korea. Park Hae-soo/AP hide caption

itoggle caption Park Hae-soo/AP

A North Korean KN-08 intercontinental ballistic missile rolls past in a military parade in Pyongyang in July to mark the 60th anniversary of the Korean War armistice. A team of U.S. researchers recently found the buildings where the North Korean military is believed to be assembling the launchers. David Guttenfelder/AP hide caption

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In this handout image provided by the South Korean Unification Ministry, Kim Kyou-Hyun (right) the head of South Korea's high-level delegation, shakes hands with his North Korean counterpart Won Tong-Yon before their meeting Wednesday in Panmunjom, South Korea. /Getty Images hide caption

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Wang Yu-chi, head of Taiwan's Mainland Affairs Council, left, shakes hands with Zhang Zhijun, director of China's Taiwan Affairs Office, before their meeting in Nanjing, China, on Tuesday. Alexander F. Yuan/AP hide caption

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Dennis Rodman in December, during one of his previous visits to North Korea. David Guttenfelder/AP hide caption

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People watch a TV news program showing North Korean leader Kim Jong Un, right, and Kim's uncle, Jang Song Thaek, circled in red, at the Seoul Railway Station in South Korea on Dec. 3. Ahn Young-joon/AP hide caption

itoggle caption Ahn Young-joon/AP

Before their split: North Korean leader Kim Jong Un, right, and his uncle, Jang Song Thaek, in February 2012. Earlier this month, Jang was executed. Kyodo/Landov hide caption

itoggle caption Kyodo/Landov