It was recently suggested to me that Pluto was downgraded from a planet to an asteroid…is this true? Is there a cite for this?
There was discussion of it a few months back, but in the end, Pluto retained its planetary status. Try Space.com’s archives.
Zev Steinhardt
Here’s a good article written by our resident Bad Astronomer that explains it all (the issues, why it’s debated, interesting factoids and so on). Sums it all up nicely but the bottom line is that today Pluto is now classified a minor planet (distinguishing it from the major ones).
Oops…I misread the article. Pluto is still classified as just a planet. Some people are proposing separating planets into two categories (major and minor) but it seems that hasn’t been accepted yet.
Pluto’s a planet?!!! That’s great news! I remember when he was only Mickey Mouse’s dog! Gosh, maybe there’s hope for Snoopy, yet!
Thanks for the follow up Whack-a-mole. You had me questioning my memory for a moment.
Zev Steinhardt
Of course, one could argue that it’s not the ninth planet, it’s the fourteenth (after Mercury, Venus, Earth, Luna, Mars, Ceres, Pallas, Vesta, Hera, Jupiter, Saturn, Uranus, and Neptune). Or you could argue that it’s the eighth, if Jupiter is actually a brown dwarf, not a planet. The definition of “planet” is really somewhat arbitrary: Until a decade or so ago, the definition was “one of dem dar nine thangs orbiting the Sun”, but since we’ve started finding extrasolar planets, that definition doesn’t really work any more.
Isn’t there some debate that the asteroid belt is rudely forgotten, because it orbits the sun just as much as any planet does?
Or something?
You know it’s a planet because a planet is larger than an asteroid. And you know something is an asteroid because its larger than a meteorite. Does that help? 
What always gets me is how Astrology people believe that your life is affected by the planets, and yet they don’t freak out when a new planet is found that screws up the whole system.
I suppose that Pluto will remain the ninth planet (although it is smaller than mercury). . Pluto became the “eighth” planet on 1979 February 7 at 10:44 UT when it came to a distance from the Sun less than Neptune. Its status as the ninth planet will remain undisputed for the next 220 years when it will once again be approaching perihelion.
Dunmurry
Unless, of course an extremely large, currently undiscovered Trans Neptunian Object reaches its perihelion, and passes inside the extreme reaches of Pluto’s orbit while it is out there.
But, TNO’s are not going to be called planets, anymore, unless they are a whole lot bigger than Pluto, cause we made that mistake once, and got over it. Pluto wins on a grandfather exemption.
Tris