Possible Ninth Planet in the Solar System: See the Evidence!

If you are a space fan, you have already heard the news -  on January 20, Caltech announced that astronomers Mike Brown and Konstantin Batygin have found evidence supporting the existence of a ninth planet in our Solar System, much bigger than Earth, and much farther away. What you may not have heard is that we can show you the evidence in the Dome Planetarium! 

This artistic rendering shows the distant view from Planet Nine back towards the sun.
Credit: Caltech/R. Hurt (IPAC)

Mike Brown is a planet finder (or maybe dwarf planet finder). He has been scouring the Kuiper Belt for years, looking for objects Pluto-sized or larger. He and colleagues discovered Eris, Quaoar, Haumea, and Makemake, all now called dwarf planets. He also discovered other Pluto-sized objects in the Kuiper Belt, including Sedna, Orcus, and about 30 other objects that do not have names. He and a colleague, Konstantin Batygin, believe there is a planet in the Kuiper Belt that is much larger than Earth. 

Using mathematical modeling, Brown and Batygin predict that the ninth planet has a mass about 10 times that of Earth, and orbits the Sun about 20 times farther away than Neptune. It would take the planet 10,000 to 20,000 Earth years to complete one orbit. 

Now, this planet is not confirmed yet. We won't be able to know for sure if it is there until we find it with telescopes. However, the evidence used to predict its existence is very strong. It is the same sort of math that was used to predict the orbit of Neptune.

Orbits of known objects were analyzed to predict the existence of a massive object orbiting the Sun. Image Credit: Find Planet Nine 

The idea that something distant and massive was lurking in our Solar System began with the discovery of Sedna by Brown and Chad Trujillo in 2004. Sedna has a very elliptical orbit, and a very long one, taking about 11,400 years to complete an orbit. Sedna's long orbit is unusual.  When it was discovered one of the possible explanations for the odd orbit was a massive object interacting with it. A few years later, Trujillo and astronomer Scott Sheppard wrote a paper describing other Kuiper Belt objects (KBO) that had perihelia (closest approach to the Sun) matching Sedna's. They proposed that an object with mass about twice that of Earth could be influencing these KBOs, but couldn't get the data to work out perfectly. Mike Brown spoke about this idea at his lecture at the Adler Planetarium last March, which we simulcast here in the Dome. He and Batygin began running simulations to try to figure out where such an object would be if it existed, and what it would be like. At first, they had limited success. Their models consistently suggested that there would be objects in the Kuiper Belt with orbits perpendicular to the plane of the Solar System.  

Brown and Batygin's model predicting Planet Nine. Image Credit

While Brown and Batygin were working on their theoretical models, another group of astronomers, Rodney Gomes and colleagues, wrote a paper describing a separate set of objects they believed were also being influenced by a distant object. These objects turned out to have orbits roughly perpendicular to the plane of the Solar System. When Brown and Batygin learned about these objects, their theory suddenly seemed very plausible, even probable. Their model ties together three mysteries of the Kuiper Belt, with the explanation being a yet-discovered, massive planet orbiting far from the Sun!  Brown and Batygin have released the probable orbit of Planet Nine in hopes that it will be discovered in the next few years. They are blogging about their search at findplanetnine.com 

A modified Plan Nine From Outer Space poster. Image Credit

If you would like to learn more, or see the orbits I described above in context, visit the Dome Planetarium at the Peoria Riverfront Museum. Every day that we are open one of our planetarium educators gives a live tour of the Solar System at 3:00 using the beautiful and powerful Uniview software. We can fly anywhere in the known Universe with Uniview, and just recently added the orbits of the Kuiper Belt objects that predict the existence of Planet Nine, and the probable orbit of the mystery planet. We'll also go to any of the other planets in the Solar System the audience suggests - you get to be the captain of our planetarium spaceship! Come visit - we love teaching about the latest news from space. You can find our schedule here. Follow us on Facebook and Twitter for daily updates!