When does a hill become a mountain?
There been quite a bit of press lately (e.g., WaPo, La Times) of the International Astronomical Union (IAU's) deliberation on what, exactly qualifies as a planet. The IAU is a group of astronomers and planetary scientists who meet periodically to decide, among other things, what acceptable names are for various planetary features and what is or is not a planet. Of recent controversy has been the discovery of several large icy bodies discovered in distant orbits beyond Nepute, which is the outermost of the gas giants. Turns out there is probably lots of trans-Neputian icy objects out there, so the question is are these planets?
The IAU seems to be leaning toward a broad as definition of a planet as possible. Is it round? Objects larger than ~480 km in diameter are pulled into a round shape by gravitational forces. And does it orbit a star, rather than other planet? Several large moons of Saturn and Jupiter, for example, are larger than the planet Mercury but do not qualify as planets. The LA Times headline summed it up best: "Round and Orbity? Must be a planet."
To me, this debate is like arguing when a hill becomes a mountain. There's no exact definition because it depends on context. What would be called a large hill if located next to larger mountains might be deemed a mountain if it were located on an isolated plain. I think this issue strikes a nerve because we like to think of the heavens as constant. The stars appear night after night (clouds permitting), and so it is disquiting to have people say there are nine planets one day, eight the next (some want to nix Pluto), and twelve the day after that (several trans-Neptunian objects with sexy names like 2003 UB313 may qualify as planets under the new definition).
Personally, I think we should a) leave the number of planets at nine or b) demote Pluto and make it eight. It turns out that Ceres, the largest asteroid, was originally designated a planet when discovered in 1801, only to be later demoted as a multitude of other asteroids were discovered. Pluto was discovered in 1930 by American astronomer Clyde Tombaugh, so American astronomers may be a bit more hesitant to demote Pluto. Here's the best take on the subject by the now defunct "Brunching Shuttlecocks," presented as a conversation between Pluto (B) and Brunching Shuttlecocks (BS):
The IAU seems to be leaning toward a broad as definition of a planet as possible. Is it round? Objects larger than ~480 km in diameter are pulled into a round shape by gravitational forces. And does it orbit a star, rather than other planet? Several large moons of Saturn and Jupiter, for example, are larger than the planet Mercury but do not qualify as planets. The LA Times headline summed it up best: "Round and Orbity? Must be a planet."
To me, this debate is like arguing when a hill becomes a mountain. There's no exact definition because it depends on context. What would be called a large hill if located next to larger mountains might be deemed a mountain if it were located on an isolated plain. I think this issue strikes a nerve because we like to think of the heavens as constant. The stars appear night after night (clouds permitting), and so it is disquiting to have people say there are nine planets one day, eight the next (some want to nix Pluto), and twelve the day after that (several trans-Neptunian objects with sexy names like 2003 UB313 may qualify as planets under the new definition).
Personally, I think we should a) leave the number of planets at nine or b) demote Pluto and make it eight. It turns out that Ceres, the largest asteroid, was originally designated a planet when discovered in 1801, only to be later demoted as a multitude of other asteroids were discovered. Pluto was discovered in 1930 by American astronomer Clyde Tombaugh, so American astronomers may be a bit more hesitant to demote Pluto. Here's the best take on the subject by the now defunct "Brunching Shuttlecocks," presented as a conversation between Pluto (B) and Brunching Shuttlecocks (BS):
BS: There are some on Earth who think you ought to be classified as a Kuiper Belt Object.
P: Me, a damn KBO? Blow me! Your Mom's a KBO!
BS: Well, you would go from being the smallest planet to the largest KBO. Any joy in the big fish / small pond theory?
P: I'm a planet. Read me lips. Pla-net. You got a problem with that?
BS: I was just making a point.
P: I've got a point to make. Bite me.
BS: So you're content being known as the smallest planet in the solar system?
P: As a planet, I get my props. When was the last time a bunch of 3rd graders stood in a line and recited the names of the 10,000+ KBOs?
posted by Bradley Thomson at 8:32 AM
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