Jason E. Andersen

Last week I dove down a rabbit hole of stellar research from the comfort of my couch. What I didn’t say, was that the rabbit hole extended so deeply that the fun facts I learned would span two weeks. For those of you that are tired of space stuff, and want me to get back to plants and butterflies, just wait patiently.

Bonus Fun Fact: Scientists believe that there is an undiscovered ninth planet orbiting the far reaches of our solar system. Researchers have dubbed it Planet Nine or, more mysteriously, Planet X. While it is purely hypothetical, evidence suggests that Planet Nine is somewhere around the size of Neptune and orbits the sun at a distance of 500 to 1,000 Astronomical Units (AU). If you consider that the most distant object we’ve observed in the solar system (so far) orbits at 132 AU, you can see why Planet Nine is yet to be discovered, if it exists at all.

But why would they think that an unknown planet exists in the first place? How could they know such things? Because of gravity and mass, friends. And, of course, math.

Imagine that you lock hands with another person, facing them, and you start to spin around each other in some sort of nauseating dance. If you are the bigger person, you won’t move very much by comparison, while a smaller person may spin around wildly or even leave the ground. The mass of one person will offset the mass of the other and thus they will spin around each other.

The solar system works in the same way, just on a much bigger scale. The mass of all the planets and stellar bodies spin around the Sun, with each exerting gravity on one another. This balancing act causes a wobble in the position of the Sun and planets as their mass offsets the mass of all the other things, much like our nauseated dancers.

Scientists can account for the mass of all solar objects and predict the wobble that should be observed. That’s where Planet Nine comes in. There is a wobble in the solar system that shouldn’t be there, given the mass of the known bodies. The best explanation for the unexpected wobble is that there is some massive body, far out in the solar system, yet to be discovered.