By Staff Writer Jerri Clewis
Every year, a lesser-known holiday comes around to pay homage to an iconic planet. On February 18th, space fans everywhere celebrate Pluto for its many charms and heartwarming nature as the once-upon-a-time planet that received an unfortunate demotion.
Before 2006, there were nine planets. Schools had handy rhymes and mnemonic sentences to help teach young children all about the planets orbiting the sun.
One of them went “My Very Educated Mother Just Served Us Nine Pizzas.”
The last word symbolized Pluto, which used to gain sympathy and admiration in classrooms for its small size and distance from the Earth. However, in 2006, Pluto suddenly lost its title, which left our solar system with only eight known planets.
Pluto was discovered in 1930 by Clyde W. Tombaugh, with contributions from William H. Pickering, in Flagstaff, Arizona. The search for the planet began in 1906 when Percival Lowell became convinced that there was a ninth planet near Uranus. His team at Lowell Observatory worked to find the planet until he died in 1916.
In 1915, a year before Lowell’s death, his observatory actually captured two faint images of the planet, but the team didn’t recognize them for what they were. Over the years prior, other observatories made the same mistake. The earliest known happened in 1909 at Yerkes Observatory.
Although Lowell didn’t manage to discover Pluto, his team continued to lay the groundwork for the planet’s eventual discovery. One step involved building the 13” Lawrence Lowell Telescope specifically to find Lowell’s “Planet X.”
In 1930, Tombaugh later discovered the planet from glass negatives made by the telescope. His discovery made headlines, and people all over the world sent in suggestions of what to name the new planet. An eleven-year-old schoolgirl in Oxford, England proposed the name Pluto and was rewarded with five pounds as a reward.
The excitement over the small planet continued, and generations of students grew up learning about the planet and the others that orbit around our sun. That all changed in 2006 when the International Astronomical Union (IAU) discovered that Pluto didn’t meet the criteria for full-sized planets.
There are three criteria for a planet to meet:
- It is in orbit around the sun.
- It has sufficient mass to assume hydrostatic equilibrium, meaning a nearly round shape.
- It has “cleared the neighborhood” around its orbit.
Pluto meets all but one of these criteria. It orbits the sun, and it has a nearly round shape. The only thing it hasn’t done is “cleared the neighborhood” around its orbit, meaning the small planet hasn’t become gravitationally dominant.
That single missing criterion led to Pluto’s demotion to dwarf planet, removing it from the lists and textbooks that had taught children for decades about the ninth planet. Yet, Pluto continues to capture hearts all around the globe despite no longer being one of the major planets in our solar system.
Perhaps, one day, Pluto will clear its neighborhood and regain its title as a full-sized planet. Until then, space fans everywhere can continue to honor the dwarf planet every February 18th.