Pluto was discovered in 1930, and was classified as a planet. In 2006, as most of us probably know, Pluto was reclassified as a dwarf planet.
A significant amount of the population, whether justified or not, are opposed to the removal of Pluto from the official list of planets, primarily out of nostalgia for one of the celestial bodies they’d known as a planet their entire lives. So what prompted this reclassification?
In March of 2005, Makemake was discovered. It, along with Eris (discovered in July 2005) and other Kuiper Belt objects, triggered the assembly of the International Astronomical Union. They had a decision to make- expand the current list of planets, or add another classification of celestial bodies. We know how that turned out.
As I was reading about this decision, it occurred to me that I knew very little about Makemake, the dwarf planet that (with Eris’s help) demoted Pluto.
Makemake is roughly two-thirds the size of Pluto. It is slightly dimmer than Pluto, but still bright enough to be the second brightest known object in the outer solar system. Its orbital path extends beyond the farthest reaches of Pluto’s path, yet Makemake orbits closer to the sun than fellow dwarf planet Eris. Despite these similarities to Pluto- size, brightness, orbit- Makemake surprisingly lacks a significant atmosphere (Pluto has one, so we would expect Makemake to have one as well). The dwarf planet’s reddish-brown color led to the conclusion that it has a layer of methane at the surface (remember, no atmosphere).
Another similarity to Pluto is that Makemake has a moon of its own, nicknamed MK 2. This moon wasn’t discovered until April 2015 when it was observed by Hubble’s Wide Field Camera 3.
I personally have quite enjoyed reading about this dwarf planet, and it make me think…If the IAU assembly had voted differently in 2006, we would have more planets (I believe the vote would have upped the number to 12). There would be a good chance we would learn about the would-be new planets nearly as much as we discuss the terrestrials and jovians. We might even devote future exploration missions to these Kuiper Belt objects. What else might be different today if the dwarf planets were just planets?
Cosmic Brownies 
I think it’s quite likely that Pluto will be recognized as a planet again soon. The definitions for a planet are quite ambiguous and will need to be ratified if the IAU wants to recognize more exoplanets as planets, as the IAU definition mandates that a planet “is in orbit around the Sun”, which doesn’t include exoplanets, and as a matter of fact, not even Earth has completely cleared its orbit, which is another planetary requirement. If these ambiguities are fixed, Pluto and other TNOs like Makemake will likely fit the new definitions!
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Hi Jack! I loved your blog post because it reminded me of a recent conversation I had over facetime with my parents. They always try (as best as they can) to be involved in my classes so they asked me about what we had learned in solar systems. They were a little bothered about when I mentioned that Pluto isn’t a planet anymore and I only had a few points of justification as to why that is (like how it hasn’t cleared its area of other objects). Your post has given me another point with more of a historical context. Also, Dan I think my parents would agree with you comment!
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I think that though keeping Pluto as one of the major planets along with these other dwarf planets would make Pluto-lovers very happy, the issue is more about important knowledge people gain and less about the formality of labels. I discovered when writing my blog post that we are still currently discovering more moons orbiting Saturn – 20 to be exact! If we still have so much that can be learned about giants such as Saturn, I think the dwarf planets can sit in the backround for a little while so we aren’t in too much over our heads.
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