Zeitblick / Das Online-Magazin der HillAc - September/Oktober 2006 - Nr. 19

Was ist ein Planet?

Hier die vollständige Definition der IAU im Originalwortlaut, beschlossen auf der IAU- Jahrestagung am 24. August 2006 in Prag:

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) shape 2], (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

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


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

2] An IAU process will be established to assign borderline objects into either dwarf planet and other categories.

3] These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.


Nach Feststellung der IAU gehört Pluto seit dem 24. August 2006 also nicht mehr zu den Planeten.

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.

Die Abstimmungen fanden zwischen 15 und 16 Uhr (Ortszeit) statt.

Zwergplanet? Hat Pluto doch eigentlich etwas mit Masse zu tun. Eins ist sicher, Pluto und Charon werden uns in ihrer Symbolik weiterhin beschäftigen. Zwerge könne sehr mächtig sein.

Lennard Wilko