Query: Novels about ancient astronauts
Relevant documents:
Edison's Conquest of Mars
Fighters from Mars
Encounter with Tiber
The Sky People
In the Courts of the Crimson Kings
Semper Mars
Across a Billion Years
High Crystal
In the Time of Dinosaurs
Jesus on Mars
Half Asleep in Frog Pajamas
The Slitheen Excursion
Ice (Johnson novel)
Silicon Embrace