Hard And Soft SF

Poul Anderson wrote fantasy and hard sf which are opposites: the supernatural and magic versus science and technology. CS Lewis and Ray Bradbury wrote fantasy and soft sf which are less contradictory. Their versions of Mars are humanly habitable although it was known when they wrote that the real Mars was not. Hard sf writers keep up to date with the science:

"You may feel that Mars itself is changing as you read through the book. Right you are... If the space probes keep redesigning our planets, what can we do but write new stories?"

-Larry Niven, Tales of Known Space (New York, 1975), Introduction, p. xii.

"...our knowledge of the cosmos is changing all the time. My universe is beginning to look hopelessly obsolete. For instance, in a Flandry tale I gave Betelgeuse planets, on some of which were life; in another, I gave Jupiter solid land masses. Both these assumptions were reasonable when I was composing, but are so no longer."

-Poul Anderson, SFWA Bulletin, Fall 1979, p. 13.

Such considerations bothered neither Lewis nor Bradbury. In Bradbury's The Martian Chronicles, a man thickens the thin air of Mars simply by planting many Terrestrial trees in Martian soil during colonization! To do this, we must get permission from someone referred to only as the Co-ordinator. This caught my attention because of the prominent role played by several figures called Coordinators in Anderson's Psychotechnic History. But Anderson's and Bradbury's sf are two different genres.