Astronauts intervene between rival Martian life-forms
Terrestrial travellers cross space in a transparent-walled ship, and the story's name for them gave French the word 'astronaute'. On Mars they find the peaceful but declining Tripèdes being pushed back by the Zoomorphes, a rival life-form that drains the vital energy of the creatures it touches. The humans take the natives' side and use their weapons against the Zoomorphes, and the narrator forms a love bond with a Tripède woman across species lines.