Arthur C. Clarke's popular 1972 novel Rendezvous with Rama, in which an asteroid collides with the earth on September 11, 2077, was a hit in more ways than one. In the book, the impact wipes out the Italian cities of Padua and Verona and plunges Venice into the sea. The coincidence of date with the terrorist attacks on the twin towers in New York helped revive interest in it.
To avoid similar disasters and detect earth-impact events ahead of time, the inhabitants of Clarke's fictional world created Project Safeguard. Someone at Nasa must have been reading that book, because 20 years later the space agency launched its own Project Safeguard to monitor the skies and assess risks.