Solar System in fiction close to the Sun and its surface was exposed to extremes of temperature. The asteroids were too tiny and airless. By the early 20th century, prospects for life in the Solar System focused on Venus, the larger moons of Jupiter and Saturn, and especially Mars. With the onset of the Space Age, planetary probes cast increasing doubt on the likelihood of extraterrestrial life in the Solar System, at least life of any magnitude greater than organisms such as bacteria. By the mid-1960s, it was firmly established that life could have no foothold on the hostile surfaces of Mercury or Venus,
Planet Stories is the folk-tale, the hero-tale of our particular niche in history". Also arguing in support of "Planet Stories", science fiction critic John Clute has commented that "the content was far more sophisticated than the covers". Bradbury's work for "Planet Stories" included two of the stories that he later incorporated into "The Martian Chronicles", including "The Million Year Picnic"; only one other story in the series had appeared before this. He also collaborated on a story with Brackett, "Lorelei of the Red Mist", based on an idea of hers, which appeared in the Summer of 1946. His stories for "Planet" demonstrate