Astronomical Error of Science

And so we now have a new 'scientific' definition for the word planet... Pluto get's to be called a dwarf planet. So now there are just eight classical planets and a whole load of dwarf planets most yet to be named. That's fine. No honestly, I mean it, it really is fine.

What's not fine is the definition.

Here's the IAU's two resolutions that were voted on and approved last Thursday:

RESOLUTION 5A
The IAU therefore resolves that "planets" and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A "planet"¹ 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.

(2) A "dwarf 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) shape² , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects³ except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".

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¹The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
²An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
³These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

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IAU Resolution: Pluto

RESOLUTION 6A
The IAU further resolves:

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.

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It all seems ok until you read the words... " has not cleared the neighbourhood around its orbit". Scientific definitions are required to be clear, concise and objective in their statements. This to me seems not at all clear and certainly not objective. How does one interpret clearing the neighbourhood? Of what? To what extent?

I'm no astronomer and I'm no scientist. I'll admit that. But I am sure that the IAU have blundered with this defintion. Somehow, the IAU consider that the eight planets from Mercury to Uranus have all cleared the neighbourhood around their orbits. Presumably of other significant celestial objects. If they want to keep along the lines of "cleared the neighbourhood around it's orbit" then they must define this much more clearly because as it stands it is far too ambiguous.

I suppose this resolution will probably stay in place for a while. I should look on the bright side... not that Pluto has much of a bright side. Pluto has joined a new class of planets called dwarfs. He might feel more at home among friends more like himself. I look forward to getting to know the names of all his new classmates.

Here's an article from the Hindustan Times that makes a very valid point:

Which of these would you say is a dog: a German Shepherd or a Chihuahua? This is the kind of question put before delegates of the International Astronomical Union (IAU) General Assembly who powwowed in Prague over Pluto's planet-hood. No wonder hardly 300 of the 2,700 astronomers at the meet even bothered to vote for, or against, stripping the ninth rock from the Sun of its planetary status and making it a 'planet dwarf' instead.

The planets in our solar system have been traditionally divided into two main groups. The inner band of relatively small worlds - Mercury to Mars - is followed by a wide gap, where the 'minor planets' or asteroids move. Beyond this is the realm of the four giants - Jupiter, Saturn, Uranus and Neptune.

Pluto's 248-year journey around the Sun is unusual for two reasons. First, its narrow, elliptical orbit edges it closer to the Sun at times than Neptune. Second, if you imagine planetary orbits as discs and look at their edges, they will appear to lie close to each other. Pluto's disc, however, is different, being tilted at an angle of 17 degrees away from Earth's orbit.

This prompts some astronomers to suggest that Pluto is not a 'real' planet, and could even be a former moon of Neptune. With new telescope technologies enabling scientists to find more and more objects orbiting far from the Sun, some of which are similar to Pluto, the clamour for downgrading the planet has become louder.

Under the new IAU guidelines, a celestial object qualifies as a planet only if it orbits a star, without itself being a star, and is large enough for gravity to pull it into a roughly spherical shape. Besides, it must dominate its orbit, clearing away other objects. Pluto's detractors point to its highly elliptical orbit, which overlaps that of Neptune, to relegate it to a new category called 'dwarf planets'.

The problem is, this will obviously also affect Earth, Mars, Jupiter and Neptune, none of which has a clear orbital zone. Earth orbits with 10,000 near-Earth asteroids, while Jupiter's path is littered with over 100,000 'Trojan asteroids' (chunks of rubble left over from the solar system's formation more than four billion years ago).

As for Neptune, if it were to clear its zone, there would be no Pluto in the first place! Astronomers would've been better off wondering what Pluto is like, rather than what it is. For only by learning more about the outer planets can we get to know more about how the inner solar system was formed.