Why Is Pluto No Longer A Planet?
As kids, we were taught about the solar system in schools. However, if you are from an older generation, you might have noticed that the solar system is considered to consist of eight planets now instead of nine.
The planet Pluto is no longer considered a planet, having been reclassified as a dwarf planet.
The possibility that a ninth planet could exist was initially suggested by Percival Lowell, whose theory stemmed from the behavior of Neptune and Uranus’ orbits. Lowell linked the fluctuations in the orbits to the gravitational pull of a possible planet and roughly calculated its position. Although the research did not yield success for long, it was once again pursued in 1929 by Lowell Observatory. With that, on the 18th of February 1930, Clyde Tombaugh discovered Pluto with the use of photographic plates and a blink microscope. Shortly following the discovery, Pluto had been announced to the public on March 13th of the same year.
Settling on a name for Pluto has its own interesting story. The name has been suggested by an eleven-year-old girl from England, Venetia Burney. Too entranced with mythology and astronomy, she proposed the name “Pluto” after the god of the underworld in Roman mythology by presumably comparing the planet Pluto, which has an estimated surface temperature below -200 °C, and the underworld.
Some astronomers questioned whether only Pluto actually affects the orbits of Uranus and Neptune considering its mass and eventually, researchers found out that not only Pluto’s mass but also that of its moon Charon had been causing the perturbations in the orbits. This was because Charon is nearly half the size of Pluto, creating what we call a double planet system.
The shift from considering Pluto a planet to a dwarf planet originally began with the understanding of Pluto’s mass, as it turned out to be lighter than researchers had expected. Thus, its gravitational pull was less than anticipated and not strong enough to cause perturbations by itself. Moreover, as astronomy has developed, astronomers have discovered other masses that were comparable to Pluto, such as Ceres and Makemake. With new findings, astronomers were encouraged to create additions to the rules of being a planet. In 2006, the definition of “planet” had been altered to consist of three conditions: the body has to be orbiting a star; the body has to have enough mass, thus gravity, to have a spherical shape; the body has to have enough mass to be gravitationally superior to other bodies in its orbit also widely known as “clearing the neighborhood”. Although Pluto fulfilled the first two conditions, it did not meet the third and was no longer considered a planet. Thus, a new category called “Dwarf planet” was established to precede similar conclusions in the future of the field of astronomy. The conditions set to be recognized as a dwarf planet included a body having to orbit the sun, having enough mass to have a hydrostatic equilibrium shape, failing to “clear the neighborhood”, and not being a satellite.
Therefore, as of 2006, Pluto was downgraded from its recognition as a planet to that of a dwarf planet due to the new criteria.
Work Cited
https://www.history.com/this-day-in-history/pluto-discovered
https://www.space.com/43-pluto-the-ninth-planet-that-was-a-dwarf.html
https://www.loc.gov/everyday-mysteries/item/why-is-pluto-no-longer-a-planet/
https://www.britannica.com/story/why-is-pluto-no-longer-a-planet
https://en.wikipedia.org/wiki/Pluto
https://esahubble.org/images/opo9014a/
