This short story is set entirely on the emperor's personal flagship/palace, which is a monumental ship full of courtiers and all the panoply of the ruler of the solar system.
He keeps a single member of a subject people as something of a court jester; this is apparently a sad representative of the benighted people of the northern hemisphere, most of whom were killed in a nuclear war that saw the balance of power shift to the southern hemisphere.
As they travel through space the captain informs them that there is an unknown object on radar. The emperor is curious and the northerner convinces the emperor's people this might actually be an artifact from outside the solar system, so something truly alien.
The emperor now must have this object, so an effort is duly made to bring it aboard. As the object nears, the captain observes that it has streaks on it as though it had made re-entry even though it is now deep in space. The captain is disturbed by this, but can't find a plausible excuse not to bring it on board.
The captain goes to the emperor to report that it is being brought onboard. At the same moment he sees the glee in the northern's face he realizes that not all weapons used in the global nuclear war were aimed down.
The time frame I believe I read this is early 1990s; could have been an anthology or a magazine. Perhaps one of the There Will Be War anthologies?