Not Final!

Not Final is a science fiction short story by Isaac Asimov, originally published in the October 1941 issue of Astounding Science Fiction, and included in the 1972 collection The Early Asimov. It is a prequel to "Victory Unintentional", although not a robot story, and one of the few stories by Asimov to postulate non-human intelligences in the Solar system.

Earth colonists on Ganymede, the largest satellite of Jupiter, have discovered the existence of intelligent life on the planet's surface. They manage to establish communication with the Jovians by means of a "radio-click" code, and exchange scientific information. When the Jovians realise that the Humans are not like them, they break off communication with a threat to leave the surface and attack what they see as inferior beings. Scientists on Ganymede discover that the Jovians can only leave the surface if they utilise force-field technology, and experimentally determine that said technology cannot be made practical - therefore the Jovians will be unable to threaten them.