In 2006, Pluto was downgraded from full planetary status to dwarf planet. This decision was met with an enormous amount of controversy. Recently, however, scientists at the Harvard-Smithsonian Center for Astrophysics have argued for the return of Pluto as the ninth planet.
Experts began questioning Pluto’s planetary status after the discovery of Eris, an object found in the Kuiper Belt beyond Neptune’s orbit. Eris was so similar in size to Pluto that many considered it as a possible 10th planet. After much public interest and debate, the International Astronomical Union (IAU) decided that a definition for the word planet must be made.
“There was no real need for a definition of planet before this,” said Richard Binzel, a member of the Planet Definition Committee and Pluto specialist at the Massachusetts Institute of Technology. “It was more like, ‘You know a dog when you see one.’ You know a planet when you see one.”
Consequently, in 2006, scientists established the criterion to define true planets. According to their definition, a planet must orbit the sun, have mass great enough that its own gravity pulls it into a round or nearly round shape, and have cleared debris from the neighborhood of its orbit. While Pluto orbits the sun like any other planet, it is much smaller and is unable to clear objects out of its path. Thus, scientists ultimately dropped Pluto from the list of the official planets.
Since this discussion, the number of planets in our solar system varies—depending on who is asked. According to some astronomers, however, our solar system contains 13 planets, five dwarf planets, and the eight major planets. As far back as the early 19th century, astronomers have believed that asteroids Ceres, Pallas, Vesta, and Juno were planets too, making the total of planets in our solar system a dozen.
Despite the creation of a planet definition, reports suggest that scientists may promote Pluto to full planetary status once again. While Pluto fans are rejoicing at the news of its return, it’s still too early to celebrate. Remember: the fate of Pluto rests in the hands of the IAU, which contains over 11,000 scientists all over the world. These scientists will have the final say on whether a Pluto is officially a planet or just an orbiting ball of ice and rock.
[Sources: NASA; USA Today]