Theoretical Planets Are Starting To Stack Up In The Outer Solar System

You may remember that about a year and a half ago, I wrote about a theoretical ninth planet way out in the outer solar system. It's thought to be an ice giant, just like Uranus and Neptune, and to orbit hundreds of AU away. If anything, that theory has gained evidence over the past 17 months. This is not about that planet. This is about a new theoretical planet orbiting in the outer solar system. Yes, if it turns out that both these planets actually exist, we'll have ten planets.

Credit: Heather Roper/Lunar and Planetary Laboratory

So, what's the story with Planet Ten? Why do we need it? Simple, it all comes down to those pesky Kuiper Belt objects again. They're not behaving the way they should be, their orbits are not in alignment with the plane of the solar system. Something is moving them, and it isn't Planet Nine, which is too far away to have the observed effect. So now we have Planet Ten, thought to be much smaller than its theoretical sibling, weighing in somewhere between Earth and Mars and looking essentially like a giant Pluto. Also, Planet Ten orbits much closer to the sun than Planet Nine, to the tune of several dozen AU rather than several hundred. So actually, Planet Ten would be the ninth planet, and Planet Nine would be the tenth planet, and that's not going to be confusing at all.

I wouldn't worry too much about having to memorize two new planet names any time soon though. It's easier to find planets around other stars than to find them around our own at this point. These planets, if they do exist, will move incredibly slowly, and give off almost no light at all. As the article says, we'll see what happens when the Large Synoptic Survey Telescope is finished and starts searching for KPOs. Until then, there's still only eight planets.