ON THIS DAY- On this day in 1964, Nikita Khrushchev unexpectedly stepped down as leader of the Soviet Union. Five years earlier, a final conference on the Antarctic Treaty convened in Washington, D.C., and, after six weeks of negotiations, the treaty was signed by 12 countries, preserving the continent for free scientific study. More recently, China became only the third country in history to launch a manned spaceflight, the Shenzhou 5, which was piloted by Yang Liwei, orbited Earth 14 times during the 21-hour flight. Born on this day in 1844 was German philosopher Friedrich Wilhelm Nietzsche and, in 1914, the fabled archetype of the seductive female spy, Mata Hari, was executed for espionage by a French firing squad at Vincennes outside of Paris.