Douglas Spencer (dougs) wrote,
Douglas Spencer

Question for proper astronomers

The new definition of "planet" is as follows:
    A "planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
Both the BBC and CNN say that Pluto was disqualified because it crosses Neptune's orbit -- and therefore that Pluto hasn't "cleared the neighbourhood around its orbit".

Surely (leaving aside questions of eccentricity) Neptune crosses Pluto's orbit and therefore hasn't cleared it's neighbourhood? Why isn't Neptune disqualified as a planet?

I suspect that Pluto has been disqualified as a planet because of its relationship with Charon, and not because of its relationship to Neptune. I've said as much in a thread here, and I've suggested that the BBC and CNN, staffed by journalists instead of astronomers, may have misreported the facts.

I'm not an astronomer, I'm a mathematician. There are some proper astronomers on my friends list. Is anyone able to offer some clarification?

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