Even in fiction there are rules, and in SF even more.

For example, before we sent space probes to Mars and Venus, people wrote SF novels imagining various things there — canals, civilizations, you name it.

After the pictures came back you could still write such a novel, but it would be a different animal, deliberately ignoring the new knowledge, and people would find it to be breaking the rules. Doesn’t mean you can’t write it, but you’ll get less respect unless you can impress people with your dramatic purpose even more than usual.