article Fall 2016

Fact or Impulsive Assumption? The Planet Nine Hypothesis

By Chris Hanko

One quality that the human race possesses that contributes so much to our technological progress is our constant desire to learn and to be curious about nearly everything. This innate curiosity has once again revealed something spectacular. On January 20th, 2016, an article was published in The Astronomical Journal about the mysterious existence of another planet in our solar system, “Planet Nine.” Although this theory is still in hypothetical stages, astronomers may be able to have physical evidence in the very near future. Get ready to change the way you think about our solar system.

The Planet Nine theory was first revealed by the ambiguity of certain elliptical orbits of objects in the far reaches of our solar system. A collection of asteroids, comets, and small ice bodies known as the Kuiper Belt has been observed to endure a distortion in orbits due to the gravitational pull of a large object, thought to be a planet beyond Neptune. Dr. Jim Lattis, director of the UW-Madison Space Place and faculty associate in the Astronomy department states, “After tracking their orbits with telescopes and cameras, a pattern emerges that all the orbits have an orientation that could not happen by chance.” This means that there is something out there creating this disturbance, and now it is up to astronomers to find out what it is.

So, let’s get into the possible physical characteristics of this so-called “Planet Nine.” Theorists believe that Planet Nine originated in the center of our solar system and was then ejected to the far reaches of the Kuiper Belt, 10 times farther from the Sun than Neptune. “The Planet, if existent, would roughly have a mass similar to Uranus and Neptune, about 10 times that of Earth’s,” Dr. Lattis hypothesizes. Based on computer simulation, Planet Nine was also calculated to be about 600 astronomical units (5.6 billion miles) away from the center of our solar system. This distance means that Planet Nine would take anywhere from 100,000 to 200,000 years to make a full revolution around the Sun. Although no composition tests have been completed, the theoretical planet is presumed to contain Hydrogen and Helium and to be a gas giant, similar to the compositions of Uranus and Neptune.

Despite these calculations, we need to keep in mind that this planet has yet to be seen by anyone, or any telescope for that matter. So what happens if this theory is completely bogus and there is not actually a “Planet Nine”? Since we are seeing an early prediction based on modeling and simulation rather than physical evidence, we cannot say with certainty that this planet exists. The alternative could be that a very large brown dwarf, a sub-star object that is too small to sustain the reactions that occur in the cores of conventional stars, passed through our solar system and changed the orbits in the Kuiper belt. This phenomenon would be very hard to detect given how dim brown dwarfs are; they emit almost no visible light and can only be identified using use infrared technology, which is very imprecise. However, the chances of Planet Nine existing are extremely high based on professional predictions.

At this point you’re probably wondering, “What about the original 9th Planet, Pluto?” In 2005, Dr. Mike Brown, a planetary astronomer from Princeton University has identified another object that he believed to be a planet in the Kuiper belt, called Eris. Eris is roughly the size of Pluto and shares many physical characteristics. However, Eris was defined as a dwarf planet, and this began a series of discoveries of multiple other common dwarf planets in our solar system. These findings eventually discredited Pluto as an actual planet in our solar system. However, the entire discussion isn’t really that consequential. “The word ‘planet’ is only a common word, not a scientific word; it’s like questioning if Plymouth Rock is a boulder or a rock,” Dr. Lattis says. Pluto should not be our main focus anymore, as Planet Nine is the main phenomenon that needs to be identified.

While astronomers can’t agree on whether or not Planet Nine exists, they can agree that it should be easily spotted with large telescopes like the Subaru Telescope located in Hawaii. This telescope can be used to find more distant and dimmer objects in our solar system than most telescopes can’t detect. A couple of months of scanning the sky in the region where the new planet is predicted to be just might provide direct observational evidence of its existence. Whatever happens next will surely keep the world curious, and we will be in the passenger seat to witness something amazing.

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