Then, how about Object Kowal? (It may have a different name now, but that is what it was called when it was discovered.) Brent --- Joe Bauman <bau@desnews.com> wrote:
To Chuck's definitions of planet I would add, for our solar system, "not a member of the Oort Cloud or the Kuiper Belt."
After Ben Bromley's talk at the SLAS meeting, we know that at least in the view of many astrophysicists, planets form through collisions of planetesimals. So it's important to distinguish a full-blown planet from these objects. Necessarily that involves somewhat arbitrary size distinctions. But we may be able to define the Oort Cloud and Kuiper Belt. If the discoverers of Sedna are right, Sedna is part of the Oort Cloud. I don't think Pluto is -- at least, it isn't anymore.
An important factor in deciding what's in the planet club and what's not is public perception. The fact that generations of school kids have learned "Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune and Pluto" should play a big role in the debate. We come off appearing arrogant if we insist, "No, everybody got it wrong! We have to take Pluto off the list!" -- especially if we do it without a compelling argument. After all, Pluto has been considered a planet for a long time, we celebrate Clyde Tombaugh's discovery, and it is not now part of a cloud of similar objects.
As Carl Sagan said, "Extraordinary claims require extraordinary evidence." In the is/isn't a planet debate, it's an extraordinary claim to say Pluto should be removed from the pantheon. It's also an extraordinary claim to add a planet.
Sedna really isn't big enough to meet the definition of planet in the public mind, I suspect. Undoubtedly, sister planetesimals will be discovered in the far reaches of the solar system. By requiring that a planet not be part of the Oort Cloud, we eliminate the extraordinary claim that Sedna should be counted as the tenth planet. And this allows Pluto to remain listed.
Just some thoughts. -- Joe
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