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Dwarf planets are not planets?

The surprising turnaround and degradation of Pluto and the other “dwarfs” by the IAU (criterion 3 for a planet) has sparked a dispute between experts and laypeople since 2006. There are good reasons to question the degradation.

Overview of the known dwarf planets
ImageOverview of currently known dwarf planets

1. The environment of planets

Current simulations show that the orbits of the planets in the solar system interfere with each other and change significantly over the course of millions of years. The clearing of an orbit is never complete, but a temporary phase in a dynamic and chaotic evolution of the orbits in the solar system. Therefore, the current state is a snapshot and makes no real sense as a definition criterion: "In principle, neither the shape or position of the orbit - nor the neighborhood should play a role in the planet definition", says planetarium director Prof. Thomas Kraupe. “After all, when describing the concept of a car, no consideration is given to whether the vehicle is off-road or on a paved road. Pluto is basically an off-road vehicle in the solar system. "

Mountains and ice rinks on Pluto
ImageMountains and ice areas on Pluto (c) NASA

2. The planetary diversity of Pluto

When the New Horizons spacecraft flew by in 2015, Pluto did not prove to be a simple, dead object near the eternal darkness, but astonished the researchers with a fascinating variety of landscapes that parallel our earth: glaciers, signs of volcanic activity and previous oceans, as well as complex organic compounds. Like most of the other planets, pluto also has several moons.

ImageSome exoplanets in comparison to Earth (c) NASA's Goddard Space Flight Center

3. The other planetary systems

The 2006 IAU planet definition is only applicable to our solar system - but does not apply to planets orbiting other stars (so-called exoplanets). This basically makes it scientifically useless - even pointless, especially since celestial bodies have long been called exo “planets”, which have much more unusual orbits compared to Pluto. Incidentally, it has so far not been possible to prove whether any exoplanet has “cleared” its orbit.

Dwarf planet Makemake
Imageillustration of the dwarf planet Makemake (c) IAU, M. Kornmesser (ESA / Hubble)

4. The insufficient involvement of planetary researchers

The planet definition of the IAU was approved without sufficient involvement of planetary researchers or planetologists. Although they - and not so much the astronomers - are responsible for the detailed geophysical/chemical analysis of the planetary bodies and their surroundings. IAU cL decision was not a scientific process. This is also evident in practical application, because the IAU definition does not play a role in practically any scientific work in planetary research and is not used in any scientific publication.

The Jagged Shores of Pluto's Highlands
ImageThe Jagged Shores of Pluto's Highlands (c) NASA

5. The scientific illusion of the definition

While young people in schools and the public have had to deal with understanding and learning the definition of the IAU since then, it is neither applied nor found access in the scientific publications in the field of planetary research. The general public is thus only given the appearance of an important scientific statement of significance. In truth, it is neither understandable nor scientifically meaningful to use.