Where is Planet X?
For decades, scientists have noticed that the gravitational pull Pluto experiences from the sun just doesn’t make sense. Right beyond the Kuiper Belt past Pluto, scientists discovered a sudden sharp decline in the number of space rocks floating around our solar system. They called it the Kuiper Cliff.
The most common explanation that we have for Pluto’s orbit and the Kuiper Cliff is a 10th (or 9th, if you want to be technical) planet. It’s been theorized for ages, even to the point that it’s become a part of pop culture. Unfortunately, no planet has ever been discovered that far out.
So, where is the extra planet? Why haven’t we found it yet? And moreover, if Planet X doesn’t exist, why does the Kuiper Cliff exist?