Planetary Systems

"Hiding Place."

"I imagine their world, though of nearly Jovian mass, is so close to its sun that the hydrogen was boiled off, leaving a clear field for evolution similar to Earth's." (p. 596)

World-building in a single sentence. Generalizing from a single instance, I used to think that every planetary system would have small planets in close orbits and gas giants further out but I gather that some other systems do have large planets near their suns.

In Robert Heinlein's Methuselah's Children and Time For The Stars, an exploratory spaceship has to approach another star to detect any planets that it might have and it might not have any. Sf has to reflect increased knowledge not only of the Solar System but also of other systems.

The Howard Families find an Earth-like planet of the Sol-like G2 star, ZD9817:

"Not only was it Earthlike but the rest of the system duplicated roughly the pattern of the Solar System - small terrestrial planets near this sun, large Jovian planets farther out. Cosmologists had never been able to account for the Solar System; they had alternated between theories of origin that had failed to stand up and 'sound' mathematico-physical 'proofs' that such a system could never have originated in the first place. Yet here was another enough like it to suggest that its paradoxes were not unique, might even be common."

-Robert Heinlein, Methuselah's Children (London, 1966), PART TWO, Chapter One, p. 123.

Future histories occupy not only alternative histories but also alternative cosmologies.