As CS Lewis points out in
Perelandra, we imagine two distinct categories of non-human intelligences:
"scientific," e.g., Martians;
"supernatural," e.g., ghosts.
We are shocked when Lewis, who, in this text, is not only author but also narrator, informs us that, on Mars, his friend Ransom had met beings that were
both extraterrestrial and supernatural - like Martian
ghosts!
Poul Anderson presents:
several races of
Martians, who are kept well within the watertight compartment of hard sf;
supernatural beings in several works of fantasy.
In particular,
The Broken Sword incorporates not only every national pantheon but also every species of folkloric sprite. Lewis rightly says that ETs and spirits are usually kept apart. Usually but not always - check out Heinlein's and Bradbury's Old Ones of Mars and Aldiss' Helliconian hereafter. See
here.
Anderson approaches a rapprochement between fantasy and sf in his inter-universal inn, the Old Phoenix. Nicholas van Rijn does business with a Martian in "Margin of Profit" and also rubs shoulders with characters from works of fantasy in the Old Phoenix in "House Rule."
Superheroes fiction, a composite genre, unites fantasy and sf on an equal footing. Morpheus (definitely supernatural) meets the last Martian (definitely scientific) who sees Morpheus in a non-human form and addresses him thus:
"Lord L'Zoril, I greet you humbly: may you guard us in the darkness and on the pathway between waking hours, and protect us in dreams from the flame of your wrath."
-Neil Gaiman,
The Sandman: Preludes And Nocturnes (New York, 1995), p. 146.
This race of Martians, not created by Gaiman but hailing, of course, from a dry planet, reacts to fire much as Krptonians react to Kryptonite.
I feel privileged to be able to navigate between these many worlds of the imagination.