In 2006, astronomers around the world decided to make the definition of a planet clear. They came up with different criteria to determine whether solid astral bodies were planets or just another piece of larger than average space debris. After these criteria were brainstormed, it was determined that Pluto did not make the cut.
It was always different from the other planets. Firstly, it is tiny, with a diameter of only 2,900 kilometers (or about 1800 miles). This is only 1/6th the size of Earth – smaller than our moon! Secondly, unlike any other planets, it is composed of almost purely nitrogen ice, with no true rock or gas within its surface. Thirdly, its orbit is highly irregular. It is very elliptical (much more so than the other planets) with an incline of a staggering 17⁰ when compared to the orbits of other planets (see the diagram below).
Now, when Pluto was evaluated, these irregularities caused many questions to arise within the astronomers studying it. If Pluto formed alongside the other planets, why are some of its key characteristics so incongruous with the rest of our solar system? Is it due to the distance it is from the Sun and the reduce gravitational pull that come with it? Perhaps, perhaps not. This statement is assuming that Pluto formed alongside our planets at all. If it did not, where did it come from? Perhaps it was a gigantic comet or asteroid pulled in permanently by the Sun’s gravitational pull.
Many other celestial bodies exist in our solar system that could be defined as dwarf planets. In fact, it is estimated, there might be around 200 such planetoids floating around in the Kuiper Belt, and even some within the much closer asteroid belt. Some of the main dwarf planets besides Pluto are Eris, Haumea, Makemake, and Ceres.
Newly discovered astral bodies are found all the time. Most, especially today with satellite imagery becoming clearer and more powerful, are discovered beyond Neptune and sometimes even Pluto. Many of them are larger than Pluto, which, if not for the dwarf planet classification, would add potentially dozens of new planets to our solar system.
Pairing such small bodies with sometimes exponentially bigger planets like Jupiter and Saturn is illogical at best. The only way to change this potential mix-up was the change the way planets are defined. Or rather, tighten the current definition up. So, in 2006, the International Astronomical Union dethroned Pluto from its status as a planet and dubbed it, along with several other astral bodies, dwarf planets.
Let’s Recap:
To make things nice and clear, a dwarf planet is generally defined in terms of four parameters. They are as follows:
- A body that orbits the Sun
- Has pulled itself into a round shape
- Is not a satellite of another body (like a moon)
- Has not cleared the rest of its neighborhood of celestial debris with its gravitational force
Pluto History:
Pluto was discovered in 1930. Due to its distance from the Sun, it remained undiscovered for thousands of years. Its existence was first theorized by Percival Lowell (1855-1916) an American astronomer who did not live to see Pluto’s discovery. He proposed that minute wobbles in the orbits of Uranus and Neptune suggested the presence of another celestial body of considerable size. In other words, a planet.
Using Lowell’s calculations, Clyde W. Tombaugh discovered Pluto on February 18, 1930. He did so using the new, powerful technique of photographic plates combined with a blink microscope. It was named Pluto, who was the Roman god of the underworld, due to its estimated surface temperature of -360 degrees Fahrenheit.
Pluto in Culture:
Pluto’s presence has made itself known in pop culture over the years.