The Mad Moon - Weinbaum's Io

Weinbaum's Io

In Weinbaum's Solar System, Jupiter radiates enough heat to create Earthlike environments on the Galilean moons. Io, the innermost Galilean satellite, has a tropical climate, so that the two human settlements are located at the poles, Junopolis in the north and Herapolis in the south. Extending partway around the equator are the Idiots' Hills, whose peaks extend beyond Io's dense but shallow atmosphere. (Weinbaum apparently didn't realize that Io is tidally locked, since he has Jupiter rise and set during the course of the story.)

There are two intelligent races native to Io: first are the loonies, a humanoid race of only moderate intelligence with large balloonlike heads at the end of long, slim necks; second are the slinkers, small and ratlike with nasty tempers. (Members of the Harrison Expedition to Mars ran across a slinker in the ruins of a Martian city in the story "Valley of Dreams".) Another Ionan life-form is the parcat, a cat-sized animal with a single hind leg and the ability to mimic sounds, including snippets of human conversation. Ionan flora includes ferva leaves, which are used by pharmaceutical companies on Earth to create medicinal alkaloids; bleeding-grass, which oozes red sap; and stinging palms, whose barbs can cause infection among humans if not treated.