The Fight for the Ninth Planet

Alan Boyle in Wired Science:

If there’s still someone out there who thinks science and politics never mix, the story behind the Battle of Prague should change your mind.

Some have cast the debate that took place in the Czech capital during the summer of 2006 as a battle against American scientists who wanted to keep the only planet discovered by an American on an unreasonably high pedestal. On the other side of the argument, there are those who suspect that the rest of the world wanted to see Pluto demoted to punish America for its unpopular foreign policy.

But we’re not talking about that kind of politics. We’re not even talking about a battle between the fans and foes of Pluto per se. Instead of thinking in terms of Republicans versus Democrats, or Plutophiles versus Plutoclasts, you have to think in terms of planetary conservatives versus liberals — or, more accurately, dynamicists versus geophysicists. The skirmishes over the definition of planethood that took place in Prague weren’t so much about poor little Pluto, but about two different ways of seeing the solar system.

One way focuses on the dynamics of a planetary system: How are things moving around, and how do those things affect one another? If a celestial body doesn’t have much of a gravitational effect on other bodies, that object is hard to detect and hard to track. If lots of celestial bodies are in similar orbits, they all tend to blur together.

Pluto may be the solar system’s brightest object beyond Neptune, as seen from Earth. It may account for as much as 7 percent of the entire mass of the Kuiper Belt, a ring-shaped region that covers more real estate than the space inside Neptune’s orbit. But because there are lots of other objects in the Kuiper Belt, dynamicists see a crowded celestial neighborhood in which Pluto doesn’t stand out…

[continues in Wired Science]


Majestic is gadfly emeritus.

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1 Comment on "The Fight for the Ninth Planet"

  1. The 4 percent of the IAU who voted on the controversial demotion resolution violated the IAU’s own bylaws by introducing a resolution on the General Assembly floor before first vetting it by the appropriate committee as required. Most attendees had already left the two-week conference assuming the initial resolution would be on the table; many have said in retrospect that had they known one small group would hijack the vote and put in a different resolution at the last minute, they would not have left early. The IAU has only made things worse by refusing to re-open this issue in spite of requests from many professional astronomers. A definition cannot just take into account where an object is; it also must encompass what that object is. This issue can be resolved by simply amending the term “dwarf planet” to indicate a subclass of planet that is a planet due to being in hydrostatic equilibrium but of the dwarf subcategory because it does not gravitationally dominate its orbit. If the IAU refuses to clean up their mess; other scientists will do this on their own.

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