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?