To Be or Not To Be A Planet: The Pluto Dilemma
Why are we hearing about Pluto’s planetary status again in 2022?
“To be or not to be a planet” seems to be the eternal debate for tiny little Pluto, the much-beloved, former ninth planet of our Solar System.
As a STEM educator and communicator who often focuses on astronomy specifically, Pluto was always one of the top ten questions to come up.
And I get it. Pluto’s official designation as a dwarf planet came out in 2006, when I was in middle school. It was confusing for teachers, parents, kids, the general public.
Why was Pluto “demoted”? How could something like a planetary classification be reversed? Had Pluto done something wrong? Now we have to change our handy dandy mnemonic for remembering the names and order of the planets!
And now, you may have seen news about how scientists and researchers want Pluto to be classified as a planet again. So what is going on? Is Pluto a planet or not and why can’t even the scientists agree?
Well to do that we have to go back a bit. Let’s dive into Pluto’s origin story because Pluto has had a complicated story from the beginning.
Pluto’s Backstory
Pluto was only discovered in 1930. Why so late? Well, because it is very small and very far away.
Pluto is 1/6 the size of Earth. Or to put it in simpler, it’s only approximately half as wide as the United States. If you drove from one coast to Middle America, you would have traveled the same distance as traveling across Pluto.
It is also, on average, 3.6 billion miles away from the Sun, or 39 times further away from the Sun than we are here on Earth.
Being both small and far away makes it doubly hard to locate in the night sky.
Since Neptune’s discovery in 1846, astronomers had hypothesized about a planet even further out. Irregularities in Uranus’s orbit hinted at something else with a strong enough gravitational field to affect the path of the seventh planet. Astronomers began searching for the mysterious “Planet X.”
Percival Lowell published his ideas on this theoretical planet in 1903, though again, he was not the first. He searched for years in his time outside of his official duties. Despite publishing estimated locations in 1915, he died the next year, unable to see his research completed.
His dream was continued eleven years after his death at his own observatory when his nephew, as part of the Board, restarted the search, securing funds for a new 13-inch telescope and the hiring of observatory assistant Clyde Tombaugh. On Tuesday, February 18, 1930, Tombaugh finally found proof of “Planet X” in the expected location.
But even so, Pluto was “never more than a speck on the emulsion of the glass photographic plates used for imaging the sky in that era” according to the Lowell Observatory. The technology of the time was limited in what it could do to study something so far away and tiny.
It was accepted into the International Astronomical Union (IAU) as a planet. We can thank an 11-year-old girl by the name of Venetia Burney of Oxford, England for giving “Planet X” the name Pluto. She suggested the name of the Roman god of the underworld to her grandfather, who passed it along to the Lowell Observatory, who accepted it as the official name of the new planet. The name also had the benefit of having Percival Lowell’s initials as the first two letters, making it the perfect choice.
So what happened?
Well, as we uncovered more and more data on Pluto over the years, decades, more questions came up. Questions in science aren’t a bad thing, in fact, they are how scientific discoveries are made.
Pluto was odd. The struggle in locating it was just the beginning.
Pluto’s orbit was very different than the other planets. Every other planet had a fairly circular orbit around the Sun and along basically the same plane (meaning the orbits essentially line up almost like rings around the Sun). This is also why they seem to line up in the night sky in a band. We don’t find any of the other planets drastically farther up or down in the sky from each other.
But Pluto’s orbit was elliptical (oval-shaped as opposed to circular), and at a severe tilt compared to the other planets. In fact, Pluto’s orbit is so wonky that at times, it can be closer to the Sun than Neptune.
We also determined that Pluto was much too small to be causing the effects we had seen on Uranus’s orbit, which began a renewed search for “Planet X,” a larger planet way in the Kuiper Belt that would be big enough to have a gravitational effect (we still have yet to locate Planet X officially).
But then, something big happened. We found lots and lots of other objects similar to Pluto out there in the Kuiper Belt (an icy asteroid belt past Neptune) with Pluto. If we classified Pluto as a planet, then all of these “Trans-Neptunian Objects” (TNOs) count as planets as well. Hundreds and hundreds of them.
Again, Pluto had always been a little different, so scientists began looking at how to classify and define a planet and if Pluto and all the other TNOs could fit into the same definition. They looked at all the other planets and compared them to each other as well as to other objects in the solar system. This research created the definition or “rules” for an object to be a planet:
- The object had to be spherical
- The object had to orbit the Sun (i.e. not orbiting another body such as the Moon orbiting Earth)
- The object had to have enough of a gravitational impact that it either pulled everything in (creating moons and causing smaller debris to fall into the planet as meteors/ meteorites) or pushed it away, creating a clear path for the orbit
Pluto was spherical and did orbit the Sun, but it consistently went into the Kuiper Belt and was being bombarded by asteroids and other material in there. Clearly, it did not fit the third requirement. And neither did the other Kuiper Belt objects. This ultimately led to the IAU’s decision to re-classify Pluto as a dwarf planet in 2006, along with the other objects in the Kuiper Belt.
This did not go over well with the general public which had grown to love its ninth planet over the 76 years. In the almost twenty years since this decision, there have been many calls from the public to reverse the decision.
The Debate and My Thoughts
There has also been scientific debate on this decision, with some still proclaiming that Pluto is a planet to them or even saying that the definition needs to be tweaked again to correctly classify everything in detail.
In the final week of 2021 and into early 2022, news broke as a group of researchers say the IAU’s 2006 decision was too hasty and we should go back to the 16th-century definition of a planet, which was “any geologically active bodies in space.”
Speaking of the impact of dropping Pluto and the other Kuiper Belt objects, Paul Byrne of North Carolina State University said the following.
“That led to the IAU — and therefore the public — adopting the “astrological” concept that Earth and the other planets were few and special, instead of a better classification that would have greatly increased the number of planets.” — NBC News
This would add many more, easily 150, objects in space to the “planet” umbrella, including geologically active moons like Europa, Enceladus, and Titan.
However, it would also disregard others. There’s currently no way to tell if exoplanets (planets that orbit stars other than our own) are geologically active.
These scientists are calling Pluto and these other Kuiper Belt objects in their research papers “planets” and are calling on the IAU to rectify its previous decision.
I do not believe that the dwarf planet classification promotes “astrological” interpretations of the Solar System that promote undue emphasis and importance on planets as Byrne suggests. It simply categorizes the objects in the Solar system in similar groups that are more easily understood by researchers and the public. Yes, the public bemoans the loss of Pluto in the planet category, but Pluto doesn’t fit into that category.
I even saw an article quoting these scientists describing the IAU’s 2006 definition as revisionist, which I find ironic. Changing it back to a 16th-century definition would be revisionist, canceling out knowledge that has been gained over the centuries.
But the most telling quote to me, as a STEM educator was the following:
“There was such interest from the New Horizons flyby [of Pluto],” said Byrne, who was not involved in the study. “But every time I gave a talk and I put up a picture of Pluto, the first question was not about the planet’s geology, but why was it demoted? That’s what stuck with people, and that’s a real shame.” — NBC News
While this is one quote from one scientist and not their main argument, this irks me. People are asking questions because they are interested and want to understand. Maybe they never heard the reason, just that it wasn’t a planet anymore. Questions are even the basis of science, but this researcher at least seems annoyed by getting this same question every time and having to answer it.
If you work in educational institutions, you know that you will get asked at least one of the top 10 hot-button questions for that given topic. Pluto’s status was just one of them when I worked at a science center and planetarium and whenever I did space programs with other organizations.
But the story itself is actually fascinating. It shows the scientific process and how we learn more and adapt our current understanding of the world as we understand more. There’s nothing wrong with Pluto. Pluto is a fascinating astronomical body and one worthy of study as are the other dwarf planets.
As an educator, I understand why they chose to create the new classification of “dwarf planet.” If we group all of these as planets, how do we teach the planets to the general public? To elementary school students? Astronomy is barely discussed as it is at that level. And it’s easy to learn about the eight planets. Yes, they could learn that there are over 150 planets and the order of the “classical” ones, but I understand the IAU’s hesitation in asking the general public and education systems to do that.
And again, Pluto is weird. It doesn’t fit the general paradigm that we had seen and continue to see of classical planets. And that’s fine. We can, should, and do still study them as fascinating objects in our Solar System. It’s just a different term on the classification system.
Our solar system is not unique. We are finding more exoplanets every day, more and more evidence that there is nothing at all special about us and that’s what makes us and the universe beautiful.
Our understanding of the world and universe has drastically changed since 1930, much less the 16th century and yet we should use 16th-century definitions? Our science should reflect the best understanding of the universe and the progress of science.
I don’t claim to understand all the details of each of these astronomical bodies as well as the scientists who research them for a living. I don’t think the current definition or wording is perfect, but what is?
All I know is that when I explain why Pluto isn’t a planet anymore, people get it. They may not love it, but they get it. Even kids. This should be an example of how science communication and education need to change. Not a rallying cry to undo a 2006 revision in favor of going back to a definition that was proven to not work and seemingly, for some at least, to deter questions they don’t want to discuss again in their lectures.
We can argue about the arbitrariness of classification systems and the word choice we use to describe those classifications, but these systems help us, all of us not just scientists, better understand the Solar System and the universe.
And I think it’s hasty to try to undo this system when it’s barely had a chance to take hold based on the number of people who are against the idea just because it’s different than what they grew up learning. There are so many things that have been reversed since we were in school, but Pluto seems to be the one that people try to revolt against.
I think the story of Pluto should be shared as a testament to science and humanity’s pursuit of science and knowledge. It should be used as a chance to explore science and its meandering ways over the years. We can use it as an opening for discussion, not a point of dissension.
What are your thoughts? Feel free to comment below and start a discussion on this amazing and much-loved body in our Solar System: Pluto.
Resources/ Works Cited:
