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rfmcdonaldSince the New Horizons flyby of Pluto, Charon and their system, I've been thinking a lot of dwarf planets.
I still agree with what I wrote in 2009 about the essential meaninglessness of the classification "planet". That in itself does not says anything about the classification of "planet" says very little about what that world is actually like. Are worlds like Europa and Titan and Enceladus less interesting because they happen to orbit larger bodies about the sun? Is Mercury more interesting? All these worlds are worlds.
I do think that there's no particular reason to classify Pluto as a planet, on account of its small mass and its failure to clear its orbit. Pluto is not like the rocky worlds of the inner solar system, not like the ice and gas giants of the outer solar system, and not even like most of the large moons inwards? It is a low-mass icy body, and quite frankly, if it is to be considered a planet, why not Ceres?.
To an extent, the identification of Pluto as a planet stems from the specific circumstances of Clyde Tombaugh's discovery of Pluto. Tombaugh was looking for Planet X, what he thought to be a body as massive as the Earth located outside of the orbit of Neptune. As Robert Coontz noted at Nature, even at the time there was some skepticism about the identification. The mystique carried through regardless, even as the mass of Pluto gradually shifted downwards.
What if Tombaugh never found Pluto in the 1930s? His discovery was highly contingent on, among other things, Percival Lowell's determination to remain involved in astronomy after the humiliation of the Martian canals. What if Pluto, brightest of the dim Kuiper Belt Objects, was found later, perhaps in the 1950s when images of other like dwarf planets--Eris, Haumea, Quaoar--were taken but not recognized by other astronomers? Might we have avoided the blind alley of Pluto as Planet X and instead come to an earlier realization of our solar system's nature, if Pluto was seen as but one of several large massive icy outer-system objects?
I still agree with what I wrote in 2009 about the essential meaninglessness of the classification "planet". That in itself does not says anything about the classification of "planet" says very little about what that world is actually like. Are worlds like Europa and Titan and Enceladus less interesting because they happen to orbit larger bodies about the sun? Is Mercury more interesting? All these worlds are worlds.
I do think that there's no particular reason to classify Pluto as a planet, on account of its small mass and its failure to clear its orbit. Pluto is not like the rocky worlds of the inner solar system, not like the ice and gas giants of the outer solar system, and not even like most of the large moons inwards? It is a low-mass icy body, and quite frankly, if it is to be considered a planet, why not Ceres?.
To an extent, the identification of Pluto as a planet stems from the specific circumstances of Clyde Tombaugh's discovery of Pluto. Tombaugh was looking for Planet X, what he thought to be a body as massive as the Earth located outside of the orbit of Neptune. As Robert Coontz noted at Nature, even at the time there was some skepticism about the identification. The mystique carried through regardless, even as the mass of Pluto gradually shifted downwards.
What if Tombaugh never found Pluto in the 1930s? His discovery was highly contingent on, among other things, Percival Lowell's determination to remain involved in astronomy after the humiliation of the Martian canals. What if Pluto, brightest of the dim Kuiper Belt Objects, was found later, perhaps in the 1950s when images of other like dwarf planets--Eris, Haumea, Quaoar--were taken but not recognized by other astronomers? Might we have avoided the blind alley of Pluto as Planet X and instead come to an earlier realization of our solar system's nature, if Pluto was seen as but one of several large massive icy outer-system objects?
