By: Alex Zapien
How should we define the solar system? Most people would point to and agree with the Merriam Webster definition: “the Sun together with the groups of celestial bodies that are held by its attraction and revolve around it”(1). For decades, people have been accustomed to the familiar names of the Sun and the nine planets that revolve around it. Thus, when the National Aeronautics and Space Administration (NASA) announced Pluto’s demotion to a dwarf planet in 2006, there was “plenty of wistful nostalgia” among the general public (2). Pluto’s demotion surprisingly revealed how the supposedly accepted definitions of a “planet” and our home solar system were not quite fixed. Once again, astronomers may need to reconsider the structure and definition of our home system: a possible ninth planet, far beyond Pluto, has been discovered.
Researchers at the California Institute of Technology have found evidence of a giant mass in the Kuiper Belt, a region of the solar system beyond the orbit of Neptune that contains many asteroids and bodies of ice more than 30 astronomical units (4.5 billion kilometers/2.8 billion miles) away from the Sun. The giant mass is 20 times farther from the Sun than Neptune and has a mass 10 times that of the Earth’s—enough to classify it as a planet.3 The supposed planet has been nicknamed by its leading discoverers, Drs Konstantin Batygin and Mike Brown, as “Planet Nine” but it is also commonly referred to as “Planet X”(3). Planet X was theorized through mathematical modeling and computer simulation but has not been observed directly. Research first began in 2015, and the news was announced in January 2016 (4). The announcement does not mean that there is officially a new planet in the solar system. Its actual existence is still being debated; however, there is serious evidence being considered.
Before Planet X’s discovery and before research officially began, one of Dr. Brown’s former postdoctoral fellows had published a paper in late 2014 suggesting that a small planet was the cause of obscure orbital features in several distant objects in the Kuiper Belt.5 Dr. Brown took this idea, and, with the help of Dr. Batygan and a few other researchers, led 1.5-year-long collaboration. Using orbital geometry, the researchers theorized the existence of an enormous planet whose gravitational pull was greatly affecting the elliptical orbits of other objects, like icy asteroids in the Kuiper Belt. The planet’s theorized existence could help explain interesting astronomical events. Indeed, in one simulation, the planet caused a set of Kuiper Belt objects (KBOs) to orbit tangentially along! (5)
Drs Batygin and Brown continue to “refine their simulations and learn more about the planet’s orbit” in hopes that research teams would be able to directly pinpoint and observe it (5). While there is currently no estimate as to when or if the planet will be found, Dr. Brown, notorious for helping cause Pluto’s dwarf-hood, remains optimistic: those upset by Pluto’s demotion can now be “thrilled to know there is a real planet to be found” such that we can “make the solar system have nine planets once again” (5). Excitement for the future has now replaced nostalgia. Despite another redefinition of our solar system, we will certainly be able to rest easy, knowing that we have a better idea of what our “home” is.
 Merriam-Webster. http://www.merriam-webster.com/dictionary/solar%20system (accessed Feb. 19, 2016).
 Grace, Francie. CBS News. http://www.cbsnews.com/news/pluto-demoted-no-longer-a-planet/ (accessed Feb. 19, 2016).
 NASA. http://solarsystem.nasa.gov/planets/planetx/indepth (accessed Feb. 19, 2016). “Hypothetical ‘Planet X:’ in Depth.”
 NASA. http://solarsystem.nasa.gov/news/2016/01/21/caltech-researchers-find-evidence-of-a-real-ninth-planet (accessed Feb, 19. 2016). “Caltech Researchers Find Evidence of a Real Ninth Planet.”
 Fesenmaier, Kimm. CalTech. https://www.caltech.edu/news/caltech-researchers-find-evidence-real-ninth-planet-49523 (accessed Feb, 19. 2016). “Caltech Researchers Find Evidence of a Real Ninth Planet.”