"The Callistan Menace" first appeared in the April 1940 issue of Astonishing Stories and was reprinted in the 1972 collection The Early Asimov. It was the second story written by Asimov, and the oldest story of his still in existence.
Asimov came up with the idea for astory, which he called "Stowaway", after his first meeting with John W. Campbell on 21 June 1938.
When his story, "Cosmic Corkscrew," was rejected by Campbell on the 23rd, Asimov started writing "Stowaway". He finished the first draft on the 28th, and the final draft on 10 July. He submitted "Stowaway" to Campbell in person during another visit on the 18th. Suspecting that Campbell would reject it, Asimov spent the subway ride home coming up with the plot for a third story, "Marooned Off Vesta".
Campbell did indeed reject "Stowaway". On 3 August Asimov submitted the story to Thrilling Wonder Stories.
When Thrilling Wonder rejected it, Asimov mailed it to Amazing Stories in Chicago, which also rejected it.
In the summer of 1939, following the sale of some later stories, Asimov revised "Stowaway", retitled it "Magnetic Death", and again submitted it to both Thrilling Wonder and Amazing, and again it was rejected.
Later that year, Asimov's friend Frederik Pohl became editor of two new magazines, Astonishing Stories and Super Science Stories. He accepted "Magnetic Death" on 16 November 1939, and it at last appeared in the April 1940 issue of Astonishing under the title "The Callistan Menace". (Asimov once described Pohl as "an inveterate title-changer".)
The scoutship Ceres has been assigned to explore the Jovian moon Callisto, outermost of the four Galilean moons. Seven previous ships had landed there over a 25-year period, and never been heard from again. Two crewmen discover a stowaway in the supply room, a thirteen-year-old boy named Stanley Fields (after Asimov's brother Stanley). The crew adopts the stowaway as a mascot, even fixing him up with an antiquated rubber space suit.
When the Ceres lands on Callisto, the crew find a previous scoutship, the Phobos, still intact. An inspection of the Phobos reveals it to be covered with dried slime, and the skeletal bodies of its crew are discovered inside.
Soon, the Callistan menace begins to threaten the Phobos.