The novella in Clarke's version of the asteroid collision theme began with a short story of the same name commissioned by Time magazine for a special edition — Beyond the Year 2000: Time Volume 140, Number 27 (Fall 1992), which he subsequently expanded to book length. Not dealing with asteroid threats, but raising the concept of humans being influenced by aliens from far beyond the solar system is the Rama tetralogy: Rendezvous with Rama (1973), Rama II (1989), The Garden of Rama (1991) and Rama Revealed (1994) (the latter three coauthored with Gentry Lee).