Earth is (obviously) not the only planet; there are many both out there in real space and in the space described in speculative literature. And, in many ways, they’re as weird in reality as they are in science fiction. The first story we know of involving (or at least self-consciously involving) travel from earth to another world was The Man in the Moone, a 1638 novel by Francis Godwin, a bishop in the Church of England. Not too long after, in 1666, Margaret Cavendish wrote The Blazing World, the first sci-fi work acknowledged to have been written by a woman. In that story, explorers could reach another planet, a bizarre utopia, by means of interstitial, rather than interstellar travel. In other words, extra-dimensional travel occurred “between the spaces” of existing 3 dimensional objects. That’s rather quantum for the 17th century.

The number of science fiction stories about alien planets proliferated in the early 20th century with serial movies and TV, and later with teleplays, movies and eventually TV shows. Special interest bloggers have made many lists of best and worst weird planets, with some planets (like the Dune planet) appearing on both best and worst lists. One list of the “worst” in the sense of terrible to visit or live on includes LV-426 from the movie Aliens, “inhospitable, lifeless and deadly” (poor, nasty, brutish and short, even) at first glance, even before the xenomorph began attacking the reluctant workers at the nearby atmospheric processing plant. This same “worst” list includes Mustafar, the planet with the lava-saturated surface in Revenge of the Sith, and Planet Number Two in the film Pitch Black, which is characterized by continuous daylight. A list at Discovery with the “best” creatively conceived and written planets includes Stanislaw Lem’s Solaris — from the novel of the same name, eventually turned into one of the best science fiction movies ever made (1972 Soviet classic, not the mediocre 2002 American remake).

Some critics have detailed arguments for why particular fictional planets are good or bad. For example, a critique in Screen Rant argues that Ego, the Living Planet, from Guardians of the Galaxy 2, is particularly irritating because the character/planet makes no sense. Why does Ego stay where he is, when he could go anywhere in the infinite universe? Why does he take the form of a human when humans are weak and unimpressive? Why would he take Mantis as a ward when she’s so needy? These are questions creators and writers should ask themselves before we have to.

But if science fiction planets appear strange, wait till you learn about some of the actual planets that have been identified. Humanity’s ability to spot extrasolar planets and speculate descriptions of them has massively grown over the past several years, and we’ve accumulated a catalogue of actually existing weirdness. There’s Tres 2B, the “darkest planet” reflecting less than 1% of all light that hits it (because it has light-absorbent gasses!) while emitting massive amounts of internal heat. And there’s 55 Cancri e, a third of which is made of solid diamond. And don’t forget GJ 1214b, a planet covered entirely with water, with a small gravity-compressed ice core. Any of these would be just as wild to visit as fictional planets, and just as ripe for speculative scenarios about rival colonies, mining outposts, or the conferral of planetary consciousness.
Ultimately, “science fiction is no more written for scientists than ghost stories are written for ghosts,” author Brian Aldiss once wrote. Elsewhere, Aldiss has written that science fiction is the search for a definition of humanity. The existence of so many unique worlds both problematizes and redefines humanity.