If Pluto isn't a planet, What is it?

Question

I think this is a scheme by the publishers of Astronomy and Science textbooks as a means to sell more textbooks.

Answer 1

According to the International Astronomical Union, Pluto is no more a classical planet but a "dwarf planet". This is mainly because the center of masses of Pluto and Caronte, its moon, is outside of the Pluto sphere.

I think it has been an unfair decision whith respect to USA people, for Pluto was the only planet discovered by US astronomers. But sometimes science needs to be hard, in order to clarify concepts.

Pluto is no more a planet, but a 'dwarf planet', as stated by a recent astronomers agreement (Praga IAU meeting, august 2006) to precisely define the terms of solar system bodies, now that a lot of are known and will be known thank to probes, telescopes, etc. Here down are the specs:

RESOLUTION 5A
The IAU therefore resolves that planets and other bodies in our Solar System, except satellites,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".

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.

RESOLUTION 5B
Insert the word "classical" before the word "planet" in Resolution 5A, Section (1), and footnote 1. Thus reading:

(1) A classical "planet"1 is a celestial body . . .

and
1The eight classical planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Answer 2

The definition of planet was changed to avoid adding tens of celestial bodieslarger than Pluto, such as the signficantly larger Eris just beyond Pluto, to our list of planets.

Instead these objects, including Pluto, are now designated the classification dwarf planet. It is not a conspiracy or agenda.

Answer 3

Well, I think it's unfair to down grade Pluto to a 'planetoid' but it is about the size of our moon. Part of the reason it was changed is it's orbit is so elliptical it sometimes is closer to the sun than Neptune.

Answer 4

It's still a planet in my definitions! Long live Clyde Tombaugh!

Answer 5

If that is their scheme (and I highly doubt that) then I hope they succeed. More science textbooks are what is needed now and less Creationist claptrap bs books.

Answer 6

i think they are calling it a dwarf planet . so when yer kid does his science project u just saved $0.45 on one less styrofoam ball

Answer 7

That is the silliest proposition I have seen on here for a fair while.

Answer 8

wasplanet