This novel was written on the basis of the best information available at the time concerning comets in general, and Halley’s Comet in particular. It was created in the awareness (and hope) that the successful 1986 Halley probes and International Halley Watch would vastly multiply our knowledge of these fascinating leftovers of creation. If some of this new information turns out to invalidate a few premises of our story, we hope at least that the reader will credit us with daring. We felt we had to tell this story now, to honor an interplanetary envoy whose visits are so well timed to once in a human span.

The authors would like to thank those experts who were of assistance, including Professors Mike Gaffey, John Lewis, John Cramer, Bert King, and Karl Johannson, as well as Dr. Ray Newburn of JPL and Dr. Eric Jones of Los Alamos Labs. Dr. Donald Yeomans of JPL and Dr. Neal Hulkower of TRW Inc. helped with orbital mechanics.

We would also like to thank Anita Everson, Joan Abbe, Richard Curtis, Sue Roberts, Dan Spadoni, Nancy Grace, William Lomax, Bonnie Graham, April Abrams and Diane Brizolara. Karen and Poul Anderson and Astrid and Greg Bear, were most gracious, also.

Dr. Louis D’Amario and Dr. Dennis Brynes of the Jet Propulsion Laboratory helped drive the plot with their wonderful calculations of planetary encounters. Each of them gets a dinner and a bottle.

And, as always, Lou Aronica of Bantam Books was understanding of the needs of authors laboring under “astronomical” deadlines.

We will be many things, in the future. But there will never cease to be a need for courage.

David Brin and Gregory Benford

September 1985