I don't see what harm it would do to give Pluto back its status of "Planet", for tradition's sake, and to honor its discover Clyde Tombaugh. Any other small planets found in the solar system's outer boondocks should get the new "Dwarf Planet" status. There are several such "mini-planets" already discovered, orbiting beyond Pluto
I have read that astronomers have found evidence that there is a very large gas giant planet much further from the Sun than Pluto, and are now searching the part of the sky where it is suspected to be.
The definition of planet the IAU came up with in 2006 was shortsighted. It was crafted to make sure that only bodies that formed from the accretion disk are planets, hence the third definition part. (By the third part, Neptune is not a planet since it has not finished clearing Pluto out of its path.)
Their whole definition falls apart when applying it to the almost weekly announcement of new planets orbiting other stars (which also violates the first part.) Do we know if those new planets have cleared their paths? Do we know if they are all in their ecliptic planes? We don't even know if they are spherical (although I don't know how they couldn't be for the size we have been finding.)
Why should it matter how a body got into orbit around a star? If we have a huge round ball orbiting, it is a planet. Doesn't matter if it is in the ecliptic or 90 degrees off. Doesn't matter if it was born there or left on the doorstep from a close stellar encounter. Should we do the same for moons? Jupiter has four moons and umpteen dwarf moons? Mars has no moons?
I would rather say we have dozens of planets orbiting the sun than the current artificial distinction. Modify the definition above to replace sun with star in the first part and get rid of the third part completely. Then just live with the idea that there are still planets orbiting the sun waiting to be discovered.
In the new paper, which the scientists plan to put forward to the IAU, the current definition is described as "technically flawed" - it only recognises planets as objects that are orbiting our Sun and not other stars. It also says the need for zone-clearing means "no planet in our Solar System" meets the criteria for planets.
The authors argue the new definition is "geophysical" and based on the physics of the world itself.
So e.g. if the positions of Earth and Pluto were swapped, the Earth would no longer be a planet according to the IAU's definition.
We constantly redefine our world based on new information.
But what's the point?
When classification for the purpose of helping or understanding, reclassification helps. But what does reclassifying what a planet is help? Classification for the sake of classification doesn't seem to be very popular.
But what does reclassifying what a planet is help?
Reclassification becomes necessary when our thinking (or models, if you will) on a certain subject cannot jive or be sustained given the new findings. (Re)classification is going on all of the time. There is already substantial resistance to it since doing so means rerunning potentially thousands of experiments and rewriting a very many papers/textbooks on anything involving it. Imagine how many things had to be rewritten/done when Einstein's theories were verified!
Let me be clear that there is no classification for its own sake going on. The sheer amount of work and potential embarrassment involved if your findings are unsound is enough to keep most people in the scientific community from doing virtually anything trivial.
You forgot one... a planet's orbit should be distinct from other planets' orbits... in other words, two planets' orbits should not cross paths...
This is true for the other 8, but Pluto cuts across Neptune's orbit, which is a big no-no.
I propose a middle ground. Let's have "planets" include "dwarf planets". We can have "major planets" and "dwarf planets" and call them all "planets" when there's no reason to distinguish between the two.
It's orbit is tilted out of the ecliptic. The orbit is sufficiently irregular that it comes inside Neptune's (every umpty-ump years...). It just doesn't match the established pattern. A reg-exp that matches "planet-like" chars would not match Pluto (sorry Percival).
Unless I missed it I'm a bit surprised that no one has mentioned that the search is presently on for the mysterious Planet 9 in our solar system. Evidence suggests that is should be there but there is a very large space where it could be apparently. NASA is crowdsourcing the search right now, so those you desperate to return to the Nine Planet Realm can participate!