Alien planets are a staple of science fiction, the canvas on which authors and directors paint the wildest things their imagination can come up with.
An ice planet? Holy shit. This is even better than your idea for a desert planet!
But because the solar system is full of seven boring uninhabitable planets and one that's getting there quickly, modern science fiction has generally looked to other stars in the galaxy for their stories to take place in. But that wasn't always the case, and once we go back a few decades, to a time when our knowledge of the solar system was based mainly on squinting really hard at the sky, all sorts of crazy adventures took place on improbable planets believed to exist right here in our own solar system.
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Or rather, less "crazy adventures" and more "unsettling adventures with strongly racist overtones."
No, not that Vulcan from the Star Trek universe, which is supposedly orbiting a star next door to ours. No, this Vulcan refers to the planet that was theorized to be orbiting the sun somewhere inside Mercury's orbit, in the star's so-called Toasty Belt.
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Some of the things I'm going to mention in this article are lies, so heads up.
This wasn't as dumb an idea as it might seem, and it was based on the fact that Mercury had a crazy ass orbit that didn't make any sense to anyone. Uranus, one of the cold bags of farts in the outer solar system, had been found to have irregularities in its own orbit, and someone worked out that this was because something big and heavy was pulling it around out there. A short search later, we found another cold bag of farts in the outer solar system, which would soon be known as Neptune.
Seconds later, a great wave smashed into the Cracked offices.
The same theory was applied to Mercury's confusing orbit, ending in speculation that there was a planet called Vulcan somewhere nearby. Inevitably a number of science fiction stories were set on its sweaty surface, many of which seemed to focus on the idea that Vulcan was hollow, like this story from the superbly named Captain Future (later turned into a 1970s anime).
Which made the odd decision to portray him as the human pilot of a spacecraft made entirely out of sideburns.
But as you've probably guessed, no one, massive sideburns or not, ever did lay eyes on Vulcan, and by the start of the 20th century we'd figured out that Mercury's strange orbit was caused by the very fabric of space being all stretched to hell around there.
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Like a sweater you took off by pulling down around your torso.
The asteroid belt between Mars and Jupiter really looks like it should have another planet there, and indeed there have been a few back-of-the-envelope-level calculations that insist that a planet should be there, and the fact that there isn't is actually pretty irritating.
Like its absence messes up the whole feng shui of the solar system.
And the fact that there's a whole bunch of rocks there instead of a planet is very suggestive that a planet might have once been there, which a few people took to calling Phaeton. In Greek mythology, Phaeton was the son of Helios and, as is so often the case with teens in Greek mythology, became a cautionary tale, in this case about driving his dad's solar chariot so poorly that Zeus destroyed him.
Which makes him kind of the Armageddon to Icarus' Deep Impact.
This idea of a destroyed planet is like catnip to a certain type of mind that doesn't get out much, and several stories have been written premised on the fact that at one point there indeed was a planet there that had simply been destroyed somehow. Sometimes it was destroyed by a collision with another planet, sometimes its inhabitants blew it up themselves. Perhaps the most famous work to mention it is Robert Heinlein's classic novel Stranger in a Strange Land, where it's ominously suggested that the Martians blew it up just because they didn't like the looks of the people who lived there.
"OHHHH! YOUR FACE!"
We're now pretty sure that there was never really a chance of that, that no planet ever could have formed between Mars and Jupiter. Jupiter's tidal influences are too strong for anything there to coalesce, bad news for anyone hoping to pen further lighthearted tales of planet-scale genocide.
"Also, your dog kept leaving space-turds on our space-lawn."