Twelve years ago, Pluto ceased to be considered a planet in the Solar System

Some believe that redefining the planet to the dwarf planet category was a triumph of scientific reasoning.

On August 24, 2006, a landmark decision made textbooks need to be rewritten. At that time, the International Astronomical Union (IAU) was hammering the definition of Pluto, what until then was the ninth planet of the Solar System was downgraded to a dwarf planet.

The decision did not happen that way overnight. These were years of intense debate, with valid arguments on both sides of the ring, and Pluto's relegation is controversial to this day. Some believe that redefining the planet to the dwarf planet category was a triumph of scientific reasoning, while others argue that the tiny world at the far reaches of the solar system is too special to be officialized as a planet.

The vote involved 424 astronomers, with Mike Brown, a Caltech researcher, officially announcing, Pluto is not a planet. There are officially eight planets in the Solar System.

Already Alan Stern, the mission leader New Horizons, the NASA said at the time: .. I'm ashamed of astronomy Less than 5 percent of the world's astronomers voted this definition 'stinks' for technical reasons.

According to the IAU, there are three main categories of objects in the Solar System:

• Planets: the eight great worlds from Mercury to Neptune,
• Dwarf planets: any circular object that is not a satellite, and has not "cleaned" the neighborhood around its orbit, and
• Small bodies: all other objects that orbit the Sun.

According to the new definition, the planet is the object that:

• It is spherical
• Orbits the Sun, but is not satellite from another planet
• Does not share its orbit with any other significant object

Thus, Pluto was eventually demoted to the category of the dwarf planet because, around it, there is a "sea" of other objects, since its gravity is not intense enough to attract them and thus clean their orbit. And like Pluto, there will be hundreds of dwarf planets, Brown said at the time - and indeed, several worlds were categorized as a dwarf planet after the IAU was redefined.