Robert Silverberg 
Aliens from Space 

Originally published in 1958, under the pseudonym David Osborne.Dr. Jeffrey Brewster, assistant professor of psycho-sociology at Columbia University, had been six weeks old when the first crude satellites were flung into space back in 1957. During his childhood there had been Moon rockets and the space stations – then the joint American-Russian-manned expedition to the Moon in 1965, right after the collapse of the Soviet dictatorship. Mars and Venus had been reached as he grew up and a permanent base was established on the Moon in 1973. Now the day’s papers reported that an expedition was ready to leave for Callisto, moon of Jupiter. But Dr. Brewster had a class to make and he was late.That was when the telephone rang and Mari, his wife, said, "Long distance from Washington." The caller was Colonel Chasin of Unsecfor – United Nations Security Force, the global and international army that policed the world in these days of relative peace and harmony…