<p>The IAU website has this <a href="https://www.iau.org/news/pressreleases/detail/iau0601/" rel="nofollow noreferrer">draft definition of &quot;planet&quot; and &quot;plutons&quot;</a> page, published on 16 August 2006 in Prague. It says (emphasis mine):</p>
<blockquote>
<p>The world's astronomers, under the auspices of the International
Astronomical Union (IAU), have concluded two years of work defining
the difference between &quot;planets&quot; and the smaller &quot;solar system bodies&quot;
such as comets and asteroids. If the definition is approved by the
astronomers gathered 14-25 August 2006 at the IAU General Assembly in
Prague, our Solar System will include 12 planets, with more to come:
eight classical planets that dominate the system, three planets in a
new and growing category of &quot;plutons&quot; - Pluto-like objects - and
Ceres. <em>Pluto remains a planet and is the prototype for the new
category of &quot;plutons.&quot;</em></p>
</blockquote>
<p>The proposed 12 planets Solar System looked like this (credit: The International Astronomical Union/Martin Kornmesser):</p>
<p><a href="https://i.sstatic.net/73N7P.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/73N7P.jpg" alt="enter image description here" /></a></p>
<p>The <a href="https://www.iau.org/news/pressreleases/detail/iau0603/" rel="nofollow noreferrer">final press release</a>, published on 24 August 2006, says:</p>
<blockquote>
<p>The IAU members gathered at the 2006 General Assembly agreed that a
&quot;planet&quot; is defined as 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.</p>
<p>This means that the Solar System consists of eight &quot;planets&quot; Mercury,
Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new
distinct class of objects called &quot;dwarf planets&quot; was also decided. It
was agreed that &quot;planets&quot; and &quot;dwarf planets&quot; are two distinct classes
of objects. The first members of the &quot;dwarf planet&quot; category are
Ceres, Pluto and 2003 UB313 (temporary name).</p>
</blockquote>
<p>Which looked like this (credit: The International Astronomical Union/Martin Kornmesser):</p>
<p><a href="https://i.sstatic.net/dJxDT.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/dJxDT.jpg" alt="enter image description here" /></a></p>
<p>So in 8 days, the IAU switched from a 12 planets system, with a planet subcategory called &quot;plutons&quot;, to a 8 planets system, with an dwarf planet category distinct from the planet category. How did that happen? It's probably something only a General Assembly attendant who witnessed the discussion would know. It must have been quite a debate!</p>

CC BY-SA 4.0
2020-11-26T08:34:44.907Z
2020-11-26T08:34:44.907Z
Jean-Marie Prival
<p><a href="https://www.iau.org/public/themes/pluto/" rel="nofollow noreferrer">This article from the IAU</a> states</p>
<blockquote>
<p>The first draft proposal for the definition of a planet was debated vigorously by astronomers at the 2006 IAU General Assembly in Prague and a new version slowly took shape. This new version was more acceptable to the majority</p>
</blockquote>
<p>What were the other proposals for the definition of a planet? What was changed between the first draft and the final version that was voted on?</p>

<history><pluto><definition>
What other definitions for a planet were proposed?
usernumber
# What other definitions for a planet were proposed?

(Asked by: username_0 on 2020-11-26)

[This article from the IAU](https://www.iau.org/public/themes/pluto/) states

> The first draft proposal for the definition of a planet was debated vigorously by astronomers at the 2006 IAU General Assembly in Prague and a new version slowly took shape. This new version was more acceptable to the majority

What were the other proposals for the definition of a planet? What was changed between the first draft and the final version that was voted on?

**Tags:** history, pluto, definition

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## 1 answers

### Answer by username_1 on 2020-11-26. Score: 4 | Accepted answer

The IAU website has this [draft definition of "planet" and "plutons"](https://www.iau.org/news/pressreleases/detail/iau0601/) page, published on 16 August 2006 in Prague. It says (emphasis mine):

> The world's astronomers, under the auspices of the International
> Astronomical Union (IAU), have concluded two years of work defining
> the difference between "planets" and the smaller "solar system bodies"
> such as comets and asteroids. If the definition is approved by the
> astronomers gathered 14-25 August 2006 at the IAU General Assembly in
> Prague, our Solar System will include 12 planets, with more to come:
> eight classical planets that dominate the system, three planets in a
> new and growing category of "plutons" - Pluto-like objects - and
> Ceres. *Pluto remains a planet and is the prototype for the new
> category of "plutons."*

The proposed 12 planets Solar System looked like this (credit: The International Astronomical Union/Martin Kornmesser):

[![enter image description here](https://i.sstatic.net/73N7P.jpg)](https://i.sstatic.net/73N7P.jpg)

The [final press release](https://www.iau.org/news/pressreleases/detail/iau0603/), published on 24 August 2006, says:

> The IAU members gathered at the 2006 General Assembly agreed that a
> "planet" is defined as 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.
>
> This means that the Solar System consists of eight "planets" Mercury,
> Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new
> distinct class of objects called "dwarf planets" was also decided. It
> was agreed that "planets" and "dwarf planets" are two distinct classes
> of objects. The first members of the "dwarf planet" category are
> Ceres, Pluto and 2003 UB313 (temporary name).

Which looked like this (credit: The International Astronomical Union/Martin Kornmesser):

[![enter image description here](https://i.sstatic.net/dJxDT.jpg)](https://i.sstatic.net/dJxDT.jpg)

So in 8 days, the IAU switched from a 12 planets system, with a planet subcategory called "plutons", to a 8 planets system, with an dwarf planet category distinct from the planet category. How did that happen? It's probably something only a General Assembly attendant who witnessed the discussion would know. It must have been quite a debate!


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