If you've seen or read 'Watchmen,' do you remember the crater on Mars with the smiley? Well, that's not just the writer's imagination. It's a real crater on Mars, known as the Galle Crater.
When Alan Moore was writing 'Watchmen,' he was using the smiley as a motif/recurring symbol in the graphic novel, and when he found out about the Galle Crater, he thought it was too good a coincidence. He set some of the plot on Mars because of this, thinking that people would think it's too farfetched for a crater to be shaped like a smiley.
Here it is on Wikipedia.
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