Jonathan Swift wrote a classic book called Gulliver’s Travels that borders on science fiction. It was written before ‘science fiction’ was what you called such books. In this book he wrote about two moons circling Mars. His descriptions of their size and orbital distance weren’t perfect but surprisingly accurate. He did this one hundred years before they were described by astronomers.
Phobos, on of Mars’ two moons
Phobos is roughly the diameter of San Francisco.