Astronomers have a long tradition of changing their minds. When Giuseppe Piazzi discovered Ceres on New Years Day in 1801, the stargazers decided it was the 7th planet as predicted by Bode's Law. Over the next few years, Pallas, Juno and Vesta were also assumed to be planets when discovered. But when the sighting of Astraea in 1845, and several more bodies almost immediately following, proved that there was a whole belt of objects between Mars and Jupiter, astronomers changed their mind and decided to demote the whole lot of them to a new category, Asteroids.
In 1930, Pluto was discovered. It was heralded as the long awaited 9th planet whose existence was predicted by many. We'll get back to Pluto in a bit.
In 1977, Charles Kowal discovered an object between the orbits of Saturn and Uranus, and the astronomers were so excited that news stories began appearing around the world with headlines like "Tenth Planet Discovered". After observing Object Kowal (soon named Chiron) for a number of months, the stargazers changed their mind and classified it as a Minor Planet. And in the mid-1980's, when overwhelming evidence arose that Chiron had a coma, they also classified it as a comet nucleus.
Jump ahead to the early 21st Century and we again find respected publications with headlines announcing the discovery of the Tenth Planet. First sited in 2003, and at first nicknamed Xena, this new 'planet' out past Pluto was thought to be larger than that body at first. For a brief moment astronomers and astrologers thought the solar system now counted ten actual planets.
But not for long. Accurate measurements of Pluto's Moon Charon surfaced in early 2006, proving that Pluto was much smaller than previously suspected, and Xena's size soon was shown to be a bit smaller as well. This did not sit well with astronomers!
There is an international organization of astronomers called the IAU that, among other things, sets various standards for astronomical classifications, and they decided that it was time to arrive at an official definition of the term Planet. Believe it or not, for centuries they had been using that word, derived from a Greek word that meant 'wandering star'. So now, with Pluto much smaller than expected, and with the possibility of a number of new bodies being discovered out beyond it, the decision was made to come up with a clear description of what was (and therefore, what was not) a Planet. In August 2006, at the IAU General Assembly (which consisted of only a small percentage of the world's astronomers, by the way), an intense and often heated debate began over this issue.
At the end, the IAU had come up with an 'official' definition, not only for 'PLANET', but had created a new category of bodies and call it 'DWARF PLANETS'. I'm going to reproduce that final resolution here:
Definition of a Planet in the Solar System
Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation "planets". The word "planet" originally described "wanderers" that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.
The IAU therefore resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way:
When the dust cleared, the world saw a lot of uproar over the vote, including some very vocal outcries from highly respected astronomers who didn't get a chance to take part in the vote. Astronomer Alan Stern, for example, started circulating a petition to overthrow the vote and rethink the whole thing! August 24, 2006 is a date that some people believe a great injustice was perpetrated.
- PLANET: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune
- DWARF PLANET: Pluto, "Xena" and Ceres
- SMALL SOLAR SYSTEM BODIES: Just about everything else - most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs),comets, and other small bodies.
So astronomers have changed their mind again! Pluto was demoted! "Xena" was demoted! And Ceres, which was a planet in 1801 and demoted to Asteroid a few decades later, was now promoted! In the mind of these astronomers, at least, these three bodies are on equal status.
Once "Xena" was no longer a planet, it's discoverer, Michael Brown, realized he couldn't name it Persephone like he had wanted to (because there was already a minor planet by that name), and was moved, because of all the discord her discovery stirred in astronomy, to name her after the goddess Eris, often viewed as the goddess of discord. I talk about Eris elsewhere on this site.
Anyway, the "Dwarf Planet" category may not last. The vote could be overturned, Pluto and Eris could one day again be planets. But I believe that these bodies were all grouped together for a very good reason: so we will look at these bodies as equal, and treat them all with the same level of importance. As astrologers we KNOW how potent Pluto is, in spite of the IAU's demotion. Well, if it is in the same league as Eris and Ceres, then we need to give them serious consideration as well.
I'd also like to toss in a personal theory here. A majority of astrologers view Pluto as being co-ruler of Scorpio. Many astrologers who have worked with Ceres (myself included) feel this body co-rules Virgo. And along with a number of other astrologers who have worked with Eris, I see much evidence that it has a major influence over the sign Libra. So these three bodies, linked together by the category Dwarf Planets, are at least partly influential over three signs that are consecutive in the Zodiac....Virgo, Libra and Scorpio. Perhaps we would not have noticed this if the bodies had not been clumped together.
And something else links these three bodies. As I mentioned, Michael originally wanted to name his body Persephone, and one of the most oft-told stories of Western mythology is that of the time Pluto stole Persephone away from her mother Ceres. This story has many levels, and has evolved over the centuries, but it is clearly a powerful story. If we look to the myths to give us additional depth in our understanding of the planets, it is clear these three are equal in their importance.