The Mad Moon

Stanley G. Weinbaum’s science fiction short story “The Mad Moon” first appeared in the December 1935 issue of Astounding Stories. It is the only tale he set on Io, and, like “A Martian Odyssey” and “Parasite Planet,” it focuses on the strange ecosystems of alien worlds.

Plot summary

In the 22nd century, protagonist Grant Calthorpe—a former sport-hunter now collecting ferva leaves for the Neilan Drug Company—lives near the Idiots’ Hills with a parcat named Oliver. To avoid stinging palms in the Ionan jungle, he bribes loonies with chocolate to gather the leaves for him. While suffering from the local “white fever” and its hallucinations, Calthorpe follows Oliver to Lee Neilan, the drug company owner’s daughter, who is also feverish.

Each mistakes the other for a vision until Calthorpe confirms her report of a newly built slinker settlement; he then rescues her from the slinkers. After restoring her health, he learns she crash-landed her aircraft against the Idiots’ Hills while trying to reach Herapolis. When slinkers undermine his shack, the pair flees into the Idiots’ Hills, hoping the thin atmosphere will stop their pursuers. In a narrow valley between two peaks, they discover a deserted city built by more-civilized earlier loonies.

When modern loonies oppose them, the slinkers form a dense mob, which Calthorpe destroys with a flame pistol. This attracts Lee’s father, Gustavus, who has been searching for her. In gratitude, Gustavus offers Calthorpe charge of a ferva plantation near Junopolis, and Lee proposes marriage.

Weinbaum's Io

In Weinbaum’s solar system, Jupiter radiates enough heat to make the Galilean moons Earthlike. Io, the innermost, has a tropical climate, so human settlements are at the poles: Junopolis in the north and Herapolis in the south.

The Idiots’ Hills extend partway around the equator, their peaks rising above Io’s dense but shallow atmosphere. Weinbaum did not know Io is tidally locked, so he shows Jupiter rising and setting in the story. Two intelligent races inhabit Io: loonies—humanoids with large balloonlike heads on long, slim necks and only moderate intelligence—and rodentine, warlike slinkers.