How many planets are in our solar system? It seems like that should be a very simple question to answer and, for most of our lives, the answer was simple: There were nine planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
But, after the Hubble Space Telescope's launch in 1990 and the construction of ever-larger telescopes on Earth in the 1990s, the floodgates opened and dozens of potential new planets were discovered. New planets must earn their stamp of approval from the world body of astronomers, the International Astronomical Union.
The flood of potential new planet discoveries caused the IAU to stop and say "Whoa! Do we really want that many planets in our solar system?"
What followed was a knock-down drag-out between the astronomers of the world over the official definition of a planet, something that had never been written in permanent ink.
During a historic meeting of the IAU in August, the number of planets in our solar system went from nine to 12 to 8 - all in one week! When the smoke cleared, there were eight planets left orbiting the sun. And Pluto had been cut from the herd. Astronomers invented a whole new class of objects in our solar system called dwarf planets. Pluto, Ceres and Eris became the charter members of this new Dwarf Planet Club.
But not everyone in astronomy-land was happy with this decision. Only 4 percent of the world's astronomers voted on the new definition for a planet. Many folks, including astronomers and non-astronomers, believe that all astronomers should be polled for a decision of this magnitude. Now, petitions are circulating for a recall vote. Many teachers and astronomers have decided to ignore the IAU's poorly thought-out definition of planet and stick with the old one. The last word in this heated debate has definitely not yet been uttered.
This leaves our solar system in a sort of astronomical limbo. New comets, asteroids, moons, KBOs and potential planets continue to be discovered every month. Today's third-graders are learning about a very different solar system than their parents learned about.
Want to know more about our new solar system? If so, join me and the Colorado Mountain College SKY Club for a special public program, "The New Solar System," on Wednesday. You'll be asked to choose sides and sit on either the "Pluto is a planet" side of the room or the "Pluto is not a planet" side of the room. Feel free to switch sides at any time during the program as the facts are laid out on the table. After the program, you can take a peep through one of our telescopes, weather permitting. Hope to see you there!