Should Pluto be reclassified as a planet?

Absolutely not. Pluto fails to effectively clear the objects in its orbit. The ratio of Pluto's radius to Charon's is approximately 1:0.51, which is far too abnormal for a planet. Moreover, Pluto and Charon are even mutually tidally locked, forever facing each other with the same side while orbiting a common center of mass. This is absolutely not a characteristic befitting a planet.

I am firmly in the "not a planet" camp. Even as a kid learning astronomy in the 1970s, Pluto seemed like an oddball.

But the "clear the neighborhood around its orbit" requirement seems like the weakest argument for Pluto's non-planetary status. Have any of the planets really cleared their neighborhoods? As others have pointed out, even Jupiter, the king of our solar system's planets, has Trojan asteroids that accompany it in its orbit. Jupiter's gravity shepherds them, but it hasn't "cleared" them from its orbit.

Clearing the neighborhood also means that a large body may not become a planet for many tens of millions of years after it forms, maybe longer, since the gravitational effects could take that long to accumulate.

Finally, if the events described in the Nice model really happened, some planets may have gained, lost, and regained planetary status, perhaps multiple times, as their neighbors moved around them.

Now, if we really wanted to, we could define planets like we define continents. As in, with no clear definition and completely subjective to whoever is talking about it!

Planets orbit the sun.

Moons orbit planets.

No. The moon orbits the earth. Mars orbits the sun. Big, big difference!

Plus, there is nothing wrong with nostalgia.

While my nostalgia gene screams at me, "It IS SO a planet!", I must bow to current definitions. It is an interesting (frustratingly so!) dwarf planet, at best.

But, as Devil's Advocate, I point out that using the definition "clear the neighborhood around its orbit” definitely demotes Pluto, the same can be said for just about every planet in our Solar System, at least. If that were truly the case, and Earth (for example) is a planet, then it would have cleared its neighborhood. Which it clearly hasn't. We are constantly bombarded by space debris, one of which wiped out the dinosaurs. Constantly...every day. And we just recently passed through the Perseids debris field. Cleared out? Not by a long shot. /"Devil's Advocate"

The concept of a name being grandfathered in should be invoked.

So the rule that applies for example to an old-fashioned street sign, a church bell that violates a new noise ordinance or an unusually narrow road. So the concept should be cosmologized as well.

The definition of what is, or is not, a planet should be simple.

By the rules given, Neptune is not a planet either. Neptune's has not cleared its orbit as Pluto's orbit intersects with Neptune's. But because of that intersection, Pluto is demoted, but Neptune is not.

Apply that rule universally or not at all.

The rule should be much simpler:

If an object orbits a star and has an atmosphere, no matter how tenuous, it is a planet. Otherwise it is not. You can call those "not planets" anything you want: dwarf planets, asteroids, etc. You can make up dozens upon dozens of rules to differentiate between the classes of "not planets".

Most projections show Pluto will still have its atmosphere, though extremely tenuous (there, but almost not), at its farthest point in its orbit from the sun. Therefore, because it orbits a star and has an atmosphere, it is a planet.

This same rule can be used with objects orbiting other stars. Simple.

The Earth's Moon does not orbit a star. Therefore it will never be a planet no matter how much anyone wants to compare it to Pluto or any other celestial object. Bringing the moon into the conversation is just plain obfuscation.

I think that most agree that objects orbiting planets could qualify as moons, but I don't understand how calling Pluto a planet means that we should start calling moons "planets". Pluto, and all the rest of the objects in the asteroid belt and Kuiper belt, could be called planets as they do orbit the sun rather than another planet. The criteria should be that a planet clears away all of the smaller objects that share their orbital vicinity.

Which are the criteria for a planet? Does Pluto orbit another planet?

Yes, Pluto should be reclassified as a Planet, because historically it was a planet.

By the way, we make every day tons of scientific mistakes, but nobody notices it, like the Indians in America. They were named Indians because the early explorers thought they had landed in the Indian peninsula, but they had nothing to do with India. The name of the early inhabitants was later changed to Amerindians, but it never caught up.

Sunset and Sunrise, it not because the Sun goes down or up, but because the Earth rotates. We should say the “Earth-end-of-the-day-rotation” or something like that. But nobody cares and sunset and sunrise are familiar expressions although not correct. Likewise, we say kilometre-hour and not kilometre per hour, the latter being right because speed is distance over time and not multiplied by time.

I could add many examples like that. I have sympathy for Pluto and I don’t like downgrading it.

Keep then Pluto as a planet or a dwarf planet, along with Ceres, Eris, Haumea, and Makemak.

But I am ready to bet with you, that Trump will require that one of these dwarf planets be named Donald Trump. Didn’t he change the name of the Gulf of Mexico and of the Lake Ontario? However, he will neve understand the difference between a moon, a planet, an asteroid, and so on.

Bernard Guillaume

I have no nostalgia for anything in the realm of empirical science, so no, Pluto as a non-planet has never purturbed me. I strive for having the scientific attitude in empirical matters, i.e., caring about evidence and having the humility to change my mind when new evidence is uncovered and also when I'm just flat wrong (I don't succeed way too many times). I'm nearly 79 so my lack of notalgia here is not because I'm too young to have any!

I’m with the scientist. Yes, Pluto, you were adopted. We still love you though, and now all these children’s authors get to write books about you. Might actually spark some badly needed early interest in science.

Mike Brown’s argument that the Moon would also be a planet is ridiculous, the Moon does NOT revolve about the Sun.

However, Pluto has NOT cleared its orbit, which is now part of the IAU definition of a planet. If Pluto were re-instated then potentially thousands of other Kuiper Belt objects have to be classified as a planets too.

Science constantly reclassifies things as new data becomes available, that is part of the scientific process

The morons who argue that nostalgia is a good enough reason need to go back to high school and revise their science clssses.

If Pluto is a planet, at least one Planet was discovered by an american astronomer. That‘s the real reason for this stupid discussion: american chauvinism!

It was a pointless waste of time. What new insight or discoveries did the renaming of Pluto bring? Answer ... None.

It was already casually regarded as the largest of the Minor Planets. (What happened to the Minor Planets?)

It was as if a bunch of geologists got together and decided that a Hill becomes a Mountain after, say, 500 meters.

(Could be difficult in the Himalayas, where the Foothills are higher than most of the world's highest mountains.)

at this time, who really cares? Go on to better things. Leave it be with caveats.

the moon is more of a rocky inner planet than pluto is an outer planet. The gas giant outer planets have nothing in common with pluto. Keep pluto as a "planet" to appease history. However, make it clear that it has more in common with an Oort cloud body than a planet. Maybe a century's long mission lander will put the debate at rest.

it would mess up textbooks.

also I agree with whoever said that it's orbit is too slow to clear its path.. and I also believe that it eventually will clear its path so instead of calling it a dwarf planet you could have called it a protoplanet... but I agree with who also said that this guy just wants to be famous by being the guy that got rid of Pluto as a planet which would have gotten him way more Fame than his so called a seven other discoveries... it's ridiculous that astronomers have nothing better to do then taking away a planets status... Neil's deGrasse Tyson gets so offended if anybody calls Pluto planet... what's it to him what anybody calls Pluto and what's it to Mr Brown.... if I look in the telescope do I get to name whatever I see.. because I see a rock rotating around the Sun and there's nothing else in its path I'm calling it a planet

I think him comparing Pluto to our moon is very misleading... because unless I'm incorrect which I didn't see anything in the article that led me to believe this, the moon rotates around Earth the other moons rotate around other planets Pluto rotates around the Sun... he didn't identify the other seven bodies he discovered but the asteroid and other worlds that should be included I'm pretty sure either stay in place or rotate around another planet... this is why Pluto was made a planet to begin with... I'm not saying that we should go and promote Pluto back to being a planet because I'm pretty sure all the scientists that vote on it would convince their colleagues to not acknowledge it ... but it appears to me that they found a way to make Pluto lose its planethood status by saying that didn't clear its neighborhood well the moon cleared its neighborhood and it's not a planet so his definition isn't well rounded and his metaphor is moot

No, Pluto is not a planet.

Rename Pluto and see what happens. Let's rename it Asphalt. See there? Just like that, nobody cares anymore.

Pluto is what it is. The words planet, moon, asteroid, and whatever are human constructs made for human convenience. It's the same argument as whether viruses are alive, tomatoes are vegetables, or hot dogs are sandwiches. You could say that planets are wandering stars and there are only five.

Humanity hasn’t agreed in how many continents are on Earth and you expect them to agree on the number of planets in the solar system?