I remember back in elementary school when another student made a science fair project and I noticed a few errors in it. One was that the solar system had eight planets. I mean, how outdated a source must that student have been using? Even if I hadn’t been an astronomy buff at that early age, I probably still could have told them that there were nine planets in the solar system.

Five extra-terrestrial planets have been known about since ancient times, since they are visible to the naked eye and can be observed changing position relative to stars (“planet” comes from the Greek word for “wanderer”). While people had inklings that they were not just points of light or some other mysterious forms of matter, it was not until Galileo that it was generally recognized that planets are worlds, like (or not quite like) our own. The original six planets did not grow in number until 1781, when William Herschel discovered Uranus (no jokes please, despite there being no real good way to pronounce that planet’s name in English). Interestingly, Uranus was first observed as early as 1690, but was not recognized for what it was, and even Herschel initially thought it was a comet. Later, he tried to name it “George’s Planet,” for the British monarch, but was overruled by the international community, which then began to set the commonly accepted rules for naming new planets.

Another celestial body was discovered between Mars and Jupiter in 1801, but was later considered not to be a planet because it was one of many objects that would later be classified as “asteroids.” That first asteroid found in 1801 was Ceres. More on that in a bit.

After that, it was a game of gravity: Uranus’ orbit was slightly off from what calculations said it should be, and so we started getting inferred planets–the idea was that the gravity of a then-unknown planet was affecting Uranus’ orbit. This led to the discovery of Neptune in 1846–although Neptune, like Uranus, was observed long before. In fact, the first confirmed sighting of Neptune was by Galileo in 1612.

Neptune’s observed orbit, however, seemed to also be unexpected, leading to another search for a planet that might be affecting the new discovery. That led to Pluto, but not immediately. It took almost a century to find the ninth planet, partly because Pluto, in fact, was not disturbing Neptune’s orbit. In fact, Neptune’s orbit was just fine–the astronomers had made a mistake in calculating the planet’s mass. But the error led to the search that finally ended in 1930, when Clyde Tombaugh, following the work of Percival Lowell, discovered Pluto. The name was actually suggested by an 11-year-old girl named Venetia Phair (which is also a cool name), and was accepted not only because it fit the rules of planetary nomenclature, but because the first two letters (now making up the planet’s sign) were evocative of Percival Lowell’s name.

But Pluto would start arguments among astronomers which would lead all the way to today’s news: is Pluto really a planet? When it’s size (smallest of the nine planets, even smaller than the Earth’s moon) and orbit (highly eccentric and well off the orbital plane of the rest of the planets) were determined, the differences between Pluto and the rest of the solar system cause many to believe that Pluto was not a planet, but some “captured” object, unworthy of planetary status. That’s where the debate remained until now.

For the past two years, astronomers have been debating the classification for what constitutes a planet, and many believed that Pluto would be demoted. Well, the results seem to be in, and though it won’t be official for another week, it seems that not only will Pluto remain a planet, but that three other objects will be added–and maps of the solar system will have to be re-written. Mind you, that’s not due to any new discoveries, only an artificial construct of vocabulary. The new definition is:

A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.

In other words, it has to be round and orbiting the sun. Kinda inclusive, don’t you think? It could lead to a whole bunch of new objects out there joining the planet club, despite being kinda dinky. Maybe they should set an arbitrary size limit as well–“you must be this tall to join the solar system.” But for God’s sake, leave Pluto in!

Pluto will indeed remain a planet, and another object, now only named 2003 UB313 (the discoverer wants to call it “Xena,” but the convention of scientists is leaning towards “Persephone”). But there are two surprises: first, Ceres will become a planet. Though part of the asteroid belt, it is big enough, and, I guess, round enough to be considered a planet. The other surprise: Charon, which until now has been recognized as one of Pluto’s moons (it has three in total). Charon will join Pluto as a planet, in a new category called “Plutons,” which describes any Kuiper Belt-like objects (beyond Neptunian orbit) that have been or may be found. Charon and Pluto may become more like co-planets rather than planet and satellite; both orbit each other presenting the same face all the time.

There are a lot of other large spherical objects out there that could in theory join the club, so stay tuned. As for me, the biggest adjustment will be fitting in “Ceres” between Mars and Jupiter–it just seems so strange, kind of like getting used to the idea that Jupiter has 63 moons. I grew up with 12; 63 just isn’t right. And I guess that’s the whole point for some people.