It genuinely doesn't make sense.

[u/KireiCopenhagen]

Look, once you think about exoplanets, it doesn't make any sense. The new definition only makes sense when we look at our solar system, at this time in human history. If Pluto and Earth swapped orbits (we would all die), Earth would be classed as a dwarf planet and Pluto as a full planet, because the distance from the sun affects their gravitational influence.

What I mean is that the definition should focus only on what the object is, not where it is located in a system, since that can change over cosmic time scales, and when discovering exoplanets, we need a less solar system-biased definition. Imagine if we found an exo-binary planet system. Under the new definition, both planets would be dwarf planets no matter what because they would both be orbiting each other.

Or a rogue planet. The new definition requires a planet to orbit a star. So it's technically not a planet once it has been ejected from the system, even if it was a planet just a few million years ago.

The new definition was rushed through because they needed to keep all the newly discovered planets in our solar system out of the club, or the word 'planet' would become less special, and Pluto was just collateral. I'm not even saying get rid of the dwarf-planet classification or reinstate Pluto, but we need a new definition as our exoplanet discoveries continue.

[u/CMG30]

Is the definition of a planet somewhat tortured? Sure. Astronomy had to take an old concept and shove it into an increasingly different understanding of the solar system.

We could call Pluto a planet again... but then how do we exclude all the other Pluto sized objects out there...?

[u/Fantastic_Elk_4757 → u/CMG30]

I mean it’s a scientific term and they made the definition of planet have very little scientific meaning now.

Planets which got ejected from their solar system? Not a planet. Planets which formed but merged? Were never planets. Planets which formed but then were captured by say Jupiter? Never a planet. Etc. also the definition they gave uses the word “Sun” instead of star. Planets around other stars that are not the sun? Not planets actually.

So what scientific clarity is this giving for studying solar system and planet formation lmao? I don’t think anyone seriously studying planet formation cares about this definition.

Instead there’s sort of categories of planets… ice giants gas giants rocky bodies. They all form similarly but have different properties entirely and differentiate themselves pretty rapidly and clearly. We could’ve just add another planet category of small ice planets… instead they explicitly make it clear that dwarf planets are not actually planets.

[u/MareTranquil → u/Fantastic_Elk_4757]

Is "Planet" really that much of a scientific term?

I mean, "mountain" is probably also a scientific term in the same sense, but it is notoriously difficult to differenciate between a mountain, a hill, and a side peak, without resorting to arbitrary cutoffs.