What was the primary nature of the classification system for planets before the 2006 IAU meeting?

Answer

Observational classification

Prior to the formalization efforts leading up to 2006, the system used by astronomers to classify major solar system bodies functioned primarily as an observational classification. This meant that acceptance into the planetary group was largely granted based on visual appearance and behavior when viewed through telescopes. An object was typically accepted if it clearly orbited the Sun and appeared distinct and sizable compared to background stars. There was a notable absence of strict, agreed-upon technical parameters regarding an object's orbital neighborhood or detailed internal structure. The status was granted based on how well it mirrored the general characteristics of the already accepted major orbiters, making the process more descriptive and reliant on precedent rather than rigorous, quantitative physical laws governing orbital mechanics.

What was the primary nature of the classification system for planets before the 2006 IAU meeting?

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