> because one thing we all agree is a planet is planet Earth!

I find this interview very interesting, because around a decade prior, Stern himself proposed 'clear the neighbourhood'[1] as a finer-grained rule for planet classification involving the dynamics of the planetary body in question. That is, planets that could clear their neighbourhoods are überplanets; otherwise unterplanets. In fact, near the end of that paper he proposes not two, but five classifications of planets: subdwarf, dwarf, subgiant, giant, and supergiant.

Now, Stern's broader argument in that interview is that we should not take into account the dynamical behaviour of planets. I disagree, especially since dynamics determine the static future state of any given object. Take chthonian planets—former gas giants whose gaseous envelopes have been stripped away by the primary. Do we insist that they are still gas giants? No, we even came up with a name for the transitory period when these planets are losing their gas envelopes.

Personally, I think Stern was being a little more animated to drum up support for and shine a beacon on New Horizons, a then-ongoing mission that he was principal investigator of.

To directly answer your question:

> If a massive object came into the solar system and perturbed orbits, caused chaos and collisions, then any "planet" with debris within its neighborhood would cease to be a planet.

There actually are (multiple) mathematical formulations for 'clearing the neighbourhood'[2]; it's not purely empirical or based on vibes. Stern proposed one in the above-mentioned paper. Jean-Luc Margot suggests several more[3]. I suspect a more universal model will be probabilistic but grounded in celestial mechanics.

> Does it realistically outweigh decades or centuries of peoples intuition of the existing definition?

People's intuition for 'planet' in the centuries before telescopes were invented was 'something that moves against the fixed background of stars'—that is literally the Greek etymon for the English 'planet'. The Sun and Moon used to be a part of the 'classical planets'. We didn't even find the last two (or three) planets in our own Solar System until around two centuries ago. We didn't know about nuclear fusion until 1925, and we didn't know other galaxies existed until similarly recently. We didn't understand the inflationary model of the universe until the 1960s. The first exoplanet was discovered only in 1992.

We have repeatedly and retroactively renamed, retconned, reworked, revamped and rewound scientific definitions and models over and over again. I think planets will be OK.

[1]: https://doi.org/10.1017/S1539299600013289

[2]: https://en.wikipedia.org/wiki/Clearing_the_neighbourhood

[3]: https://doi.org/10.1088/0004-6256/150/6/185

I find it particularly amusing that the IAU definition, in a footnote, expressly declares the eight planets to be what they are. In other words, the true definition for being a planet is to be defined as a planet- so the criteria it gives are entirely superfluous, at least when it comes to our own solar system.

It's clear that they worked backwards from the eight planets to come up with a classification system that fit, but in realizing the problems with the approach, just gave up and created the carve-out.

Also, just as another example of the absurdity of the IAU definition, there's a pretty strong argument to be made that Earth's moon would be a planet under the criteria: it orbits the sun, it's round, and it's massive enough / positioned such that it's capable of clearing its neighborhood.

« If a massive object came into the solar system and perturbed orbits, caused chaos and collisions, then any "planet" with debris within its neighborhood would cease to be a planet. »

Major impacts on Earth on a regular basis would indeed upset the applecart of planetary taxonomy.

Arguably there are just two categories: stuff and not-stuff (aka vacuum). And then you go from intergalactic space (almost entirely not-stuff) via interstellar space (marginally more stuff) through planets and stars up to neutron stars (lots of stuff) to black holes (well, we don't actually know what is inside a black hole exactly, our models break down).

Is this classification useful for everyday life? Not at all, but looking at things from different perspectives for a change can be quite amusing.

It doesn't work for exoplanets because part of the definition is orbiting our Sun. But the exoplanet definition would define the same 8 for our star, so I don't really see where the issue is.

> I think the backlash was fed by insistence dwarf planets are not just a subtype of planets[...]

I'm 99.9% certain that the backlash would have been far greater if our solar system suddenly had dozens extra planets.

> But you never hear people explaining why the IAU insists "dwarf planets" aren't "planets" even when "dwarf planets" has several subcategories which don't share the "planet" moniker[...]

Because otherwise the definition would differ greatly from our historical classification. Since it is necessarily arbitrary, sticking close to our history IMO seems like the obvious choice.

They are a separate category and it can clearly be demonstrated.

It would make the mnemonic for memorizing the order of the planets very long and difficult for the children to remember.

My Very Elegant Mother Just Served Us Nachos

Fifty is an undercount by many orders of magnitude. Several thousand TNOs have been cataloged, there are probably millions of them.

Setting aside the whole "demote Pluto" and "dwarf planet" aspects, I find it amusing that we use the same term for small rocky Mercury (2,440 km radius, 5% of Earth's mass) and immense gaseous Jupiter (69,000 km radius, over 300 times Earth's mass). Only we don't, of course. Jupiter is a gas giant, while Mercury is a rocky planet, or iron planet; there's a lot of 'planet' terminology.

https://en.wikipedia.org/wiki/List_of_planet_types

Ultimately these sorts of quibbles are fundamentally semantic in nature thus (in general) entirely pointless. It's only the subjects themselves - the myriad celestial bodies - that are interesting.

You can just keep calling it a planet in everyday conversation if that's your jam. There's no astronomy police that will come to get you if you do.

Just expect to be corrected and "well, achually"-ed by people who follow the current naming system, especially in science circles.