New research suggest Pluto should be reclassified as a planet

September 7, 2018, University of Central Florida
Should Pluto be reclassified a planet again? UCF scientist Philip Metzger says yes based on his research. Credit: NASA

The reason Pluto lost its planet status is not valid, according to new research from the University of Central Florida in Orlando.

In 2006, the International Astronomical Union, a global group of astronomy experts, established a definition of a planet that required it to "clear" its orbit, or in other words, be the largest gravitational force in its orbit.

Since Neptune's gravity influences its neighboring planet Pluto, and Pluto shares its orbit with frozen gases and objects in the Kuiper belt, that meant Pluto was out of planet status.However, in a new study published online Wednesday in the journal Icarus, UCF planetary scientist Philip Metzger, who is with the university's Florida Space Institute, reported that this standard for classifying is not supported in the research literature.

Metzger, who is lead author on the study, reviewed scientific literature from the past 200 years and found only one publication—from 1802—that used the clearing-orbit requirement to classify planets, and it was based on since-disproven reasoning.

He said moons such as Saturn's Titan and Jupiter's Europa have been routinely called planets by since the time of Galileo.

"The IAU definition would say that the fundamental object of planetary science, the planet, is supposed to be a defined on the basis of a concept that nobody uses in their research," Metzger said. "And it would leave out the second-most complex, interesting planet in our solar system.""We now have a list of well over 100 recent examples of planetary scientists using the word planet in a way that violates the IAU definition, but they are doing it because it's functionally useful," he said."It's a sloppy definition," Metzger said of the IAU's definition. "They didn't say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit."

The planetary scientist said that the literature review showed that the real division between planets and other celestial bodies, such as asteroids, occurred in the early 1950s when Gerard Kuiper published a paper that made the distinction based on how they were formed.

UCF Scientists Philip Metzger is a co-author on the paper questioning the logic behind Pluto's classification. Other authors include Mark Sykes, of the Planetary Science Institute; Alan Stern, of the Southwest Research Institute; and Runyon of Johns Hopkins University Applied Physics Laboratory. Credit: University of Central Florida

However, even this reason is no longer considered a factor that determines if a celestial is a planet, Metzger said.

Study co-author Kirby Runyon, with Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, said the IAU's definition was erroneous since the literature review showed that clearing orbit is not a standard that is used for distinguishing asteroids from planets, as the IAU claimed when crafting the 2006 definition of planets.

"We showed that this is a false historical claim," Runyon said. "It is therefore fallacious to apply the same reasoning to Pluto," he said.Metzger said that the definition of a planet should be based on its intrinsic properties, rather than ones that can change, such as the dynamics of a planet's ."Dynamics are not constant, they are constantly changing," Metzger said. "So, they are not the fundamental description of a body, they are just the occupation of a body at a current era."

Instead, Metzger recommends classifying a planet based on if it is large enough that its gravity allows it to become spherical in shape.

"And that's not just an arbitrary , Metzger said. "It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body."

Pluto, for instance, has an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons, he said.

"It's more dynamic and alive than Mars," Metzger said. "The only planet that has more complex geology is the Earth."

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setnom
2.6 / 5 (13) Sep 07, 2018
"If you take that literally, then there are no planets, because no planet clears its orbit"

Clearly the definition has to be revised. But not to again elevate Pluto to planet. No, the definition has to be revised to specifically include what they mean by "clearing the orbit", because even the scientist this article mentions is mistaken, according to the above quote.

For the IAU, "clearing the orbit", means clearing it of objects of the same size or larger. This is the correction that should be made.

Example:
- There is no object, with the size of the Earth or larger, in Earth's orbital neighborhood;
- There is no object, with the size of Neptune or larger, in Neptune's orbital neighborhood;
- Pluto has Neptune (larger object) in its orbital neighborhood, therefore it fails to fit the definition.
Shakescene21
4.7 / 5 (12) Sep 07, 2018
This whole dispute is over nomenclature rather than basic scientific principles. Furthermore, both sides have good points, and I don't have a problem either way. I'm happy with calling Pluto a "dwarf planet" as distinct from a "major planet".
Steelwolf
3.9 / 5 (7) Sep 07, 2018
Seeing as how it is not a moon of Neptune and follows it's own orbital pattern, it Should be classified as a planet, whether you want to put 'dwarf' in front of it or not. It is spherical, it follows it's own orbit, and is the center of mass for other objects, IE Charon and the smaller partners. Even Dwarf Double-planet works considering the properties of Charon, as even the Earth is known to be a binary planet structure anyhow, since the moon is a sphere. We call it a moon, but even that is just a class of planetary sized items, even though around other planets some moons are more akin to asteroids IE Mars' Phobos and Deimos.

The idea of orbit clearing always was a silly idea when applied literally, look at the Jovian Lagrange Points, they are by no means 'clear'. And we have comets incoming all the time crossing planetary lanes, so that should have been a non-starter to begin with.
Gigel
1.9 / 5 (9) Sep 07, 2018
This is what you get when you don't have a sensible human at the place you talk about. We could as well let automated probes give a definition for "planet". Or we could change definitions until a person gets there and gets to collect actual evidence for a proper definition of "planet". I'd say we send someone there. We could use a nuclear rocket and have some actual information from the place in 1-2 years and finally set it straight whether it's a planet or something else.

And better land him on the spot.

I mean Spain sent 3 ships full of convicts to the edge of the world 500 years ago and we couldn't get 1 person to Pluto for a proper definition of the place?
Iochroma
3.9 / 5 (7) Sep 07, 2018
Well, then Eris ("Xena") must also be a planet.
Anonym471830
3.8 / 5 (13) Sep 07, 2018
Astronomers at the IAU are quite presumptuous if they think they have the authority to define "planet" without agreement from planetary scientists.

Now, I don't mind calling Pluto a "dwarf planet", as long as the definition gets updated so that a dwarf planet is a type of planet. Currently it's NOT. That's right folks, the current IAU definition says that a dwarf planet is not a type of planet. That's like saying that a dwarf human is not a human.

By this stupid IAU definition, a rogue planet is not a planet either. It's just a "thing". Originally, the original Greek word planētai just meant wanderer. It's been hijacked by astronomers wanting to shake things up and make a name for themselves. Quite shameful, really.
Parsec
3.5 / 5 (8) Sep 07, 2018
The primary reason that the IAU concocted this bizarre planet definition was to exclude various bodies (Ceres, Vesta, etc.) from being included as planets.

The main difficulty that this definition has is that it relies on the way bodies interact with each other in its definition. In other words, I should be able to look at only the characteristics of the body itself, independently of any external objects, to determine its definition.

Consider the current definition of a moon. This is an object whose orbit's center of rotation is closest to a non-stellar object. Since stars are usually easily defined, this is usually not problematic. But what happens when you have an object in orbit to a brown dwarf or "failed star"?

In addition, how do you define a "planet" that which is orbiting the center of the galaxy (so called "free floating planets")?

The problem with the IAU definition is that it is inconsistent, not that it excludes Pluto.
rrwillsj
3.7 / 5 (6) Sep 07, 2018
Well, maybe I'm wrong but if "globular" is the criteria? Wouldn't that have to include Ceres? Though I do not think it has a currently active geology?

Luna as a "planet" could be questioned since whatever currently active geology is occurring is probably the result of exterior tidal forces.

Again, this goes back to my Theory of Stupid Design. Every tome we turn around, we keep getting more categories, with more outlier variations to classify stars and planetary bodies.

And you can make all the rules you want... What to call a orbiting body. Or how to classify an object or a star or a phenomena. And somebody is going to argue with you. Demanding acceptance of their system of designating whatever they have a bee n their bonnet about!

Meanwhile.... The Public doesn't give a rats ass about your delusions of authority. They will stubbornly stick to whatever terms they can vaguely remember from their secondary school science classes.
elevyn_11_
3.7 / 5 (9) Sep 07, 2018
god, my heart cannot take the uncertainty
granville583762
3 / 5 (8) Sep 07, 2018
An orbit does not designate a planet
If the sun shared its orbit with a star, does it loses its designation as a star
The rule, clearing ones obit - how is it applied to binary planets, the earth is sharing its orbit with the moon as there's talk of making the moon a planet - so what it shares its orbit with another planet - An orbit, a planet does not make!
holoman
3 / 5 (3) Sep 07, 2018
No one gives a hoot, especially me.
Arrowstone
2.8 / 5 (5) Sep 07, 2018
The current state of affairs seriously messes with my 2nd grade memorization. Now I go Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus (boy the flack you get if you say this wrong (or right?)!), Neptune, .... Please bring back planet nine so I don't have to sound like I fell over the end of something! The grandkids tease me and ... hoo boy! Pluto I love you!
eljo
3 / 5 (5) Sep 07, 2018
Instant respect for the scientist.
Old_C_Code
4 / 5 (4) Sep 07, 2018
Gran: the moon orbits Earth, they are not in a binary orbit.
granville583762
2.5 / 5 (11) Sep 07, 2018
There are subtleties at work here
The people who designated Planet Pluto not a planet have clearly to go back and study Sir Isaac Newton's Gravity, because they clearly do not understand its subtleties
Old_C_Code> Gran: the moon orbits Earth, they are not in a binary orbit.

The moon orbits the earth, where as the earth orbits the moon - the earth attracts the moon, where as the moon attracts the earth - earth's gravity attracts the moon, where as the moons gravity attracts the earth.
To realise this subtlety, if the earth's gravity was neutralised, the earth would continue orbiting the moon.
JongDan
3.9 / 5 (7) Sep 07, 2018
Wouldn't that have to include Ceres? Though I do not think it has a currently active geology?

Yes, Ceres does have an active geology. It's ancient impact basins have managed to flatten out somehow, and it has a single cryovolcano – Ahuna Mons, which is estimated at about 200 million years old. Which I guess qualifies it as active.
HannaB
1 / 5 (2) Sep 07, 2018
Why not - but there is already quite a lot of similar planets like Pluto after then...
Mark Thomas
3 / 5 (6) Sep 07, 2018
A planet is a sub-stellar, celestial body at least 2,000 kilometers in diameter.


By that definition, we have ten known planets in the solar system including Pluto and Eris. Orbits are irrelevant so rogues and exoplanets are all included. Many subtle advantages to this definition, including its brevity and precision.
TorbjornLarsson
2.5 / 5 (6) Sep 07, 2018
By appealing to history they only strengthen the new definition. It is scientifically based, later extended to exoplanets, and democratic. The astronomical planet definition also avoids the problems of the astrophysical planet definition they appeal to: round objects are not always differentiated or even solid (say, stars), the asteroid and Kuiper and Oort belts have too many objects to name.

"clearing the orbit", means clearing it of objects of the same size or larger.


I don't think it is correct. The paper that the definition is based on looks at clearing by dominating, so remaining mass is less than the planet mass. One or several orbit-sharing bodies that are as large or sum to larger would mean it has not been able to clear by dominating.

It is a very good concept for our system, since Pluto easily fails while the others do not. When looking at other systems, if they are > 0.5 Gy (easily seen) the planets and debris (Pluto analog) disks stand out.
TorbjornLarsson
2 / 5 (4) Sep 07, 2018
Astronomers at the IAU are quite presumptuous if they think they have the authority to define "planet" without agreement from planetary scientists.


They did not think that, they considered the astronomical planet definition only. The astrophysical planet definition is different, useful for its purpose, and alive and well. (Though as I noted in my longish comment the paper authors are wrong in that rounded automatically means solid and differentiated.)

C.f. the many species concepts in biology, different uses, no problem.

A nomad planet is a different class, but technically it dominates its "orbit" (if defined as rocket scientists define it, any trajectory). So I don't see how dragging them into the analysis (they are outside the astronomical planet definition, I think) would help rounded debris objects become planets.
Surveillance_Egg_Unit
3.3 / 5 (7) Sep 07, 2018
Dr. Metzger is a true visionary. It is about time that Pluto took her rightful place as a planet again.

Even human dwarves like to think of themselves as men and women.
granville583762
3.5 / 5 (8) Sep 07, 2018
As it always was, still is and will always be, simply, Planet Pluto
SEU> Dr. Metzger is a true visionary. It is about time that Pluto took her rightful place as a planet again.
Even human dwarves like to think of themselves as men and women.

If we do not act fast, Planet Pluto will not be even a dwarf planet, its well on its way to being designated a ball of ice - If it can be so lucky.
flashgordon
2.7 / 5 (3) Sep 07, 2018
The fact that researchers a few hundred years ago don't use the clearing of the path definition of a planet is not a logical deduction.

I was struck that Philip Metzger pointed out "what defined a planet from an asteroid?" I this is the right question. And the answer is partly that of sphericity. But, I've been arguing that what distinguishes a planet from an asteroid is that of element differentiation. The heavy elements diffuse to the core, surrounding the spherical surface of lighter elements.

I wrote a blog entry about it awhile ago. I've shared it with Mike Brown. He pointed out some rather obscure asteroid, which didn't really disprove my definition. i forget which, and that twitter account got shut down(I have a bad habit of getting twitter accounts closed. I really don't believe they were justified in shutting them down.)

http://wwwscienti...day.html
ShotmanMaslo
3 / 5 (4) Sep 08, 2018
It is estimated that there are 200 dwarf planets similar to Pluto in the Kuiper belt, and possibly more than 10,000 in the region beyond. So if you want to keep Pluto a planet, then there will inevitably be thousands of planets in the solar system. Clearly a distinction needs to be made between these two categories. Current definition makes sense in my opinion.
arcmetal
3.5 / 5 (8) Sep 08, 2018
It is estimated that there are 200 dwarf planets similar to Pluto in the Kuiper belt, and possibly more than 10,000 in the region beyond. So if you want to keep Pluto a planet, then there will inevitably be thousands of planets in the solar system. Clearly a distinction needs to be made between these two categories. Current definition makes sense in my opinion.

It is like saying there are too many rivers on Earth, so some will need to be called something else.
NoStrings
1 / 5 (2) Sep 08, 2018
Give it up, find something useful to research; if you are capable? Are you Pluto's attorney?

The world is full of regressors, royalists, etc.

And Pluto is TINY too. As ShotmanMaslo says, there may be hundreds of Plutos.
Cool alcohol collection nevertheless!
thingumbobesquire
3 / 5 (2) Sep 08, 2018
What is your definition of definition?
Mark Thomas
3 / 5 (8) Sep 08, 2018
Except predictions of hundreds of Plutos turned out to be wrong. That is what some astronomers argued in 2006 when they threw together the current planet definition, but against all their expectations, the largest known body in our solar system beyond Neptune (TNO) is still Pluto, with Eris as a close second. After that there is a considerable gap between Eris and the next largest TNOs. The 6th or 7th largest TNO after Eris is smaller than Ceres.

https://en.wikipe..._by_size
ellbeeyoo
2 / 5 (4) Sep 08, 2018
There are a number of objects, not visible to the naked eye and impossible for the backyard astronomer to find, that are larger than Pluto. They too would have to be classified as planets. There may be something outside even Pluto's orbit, but still orbits the sun. It too would have to be a planet. There may be additional objects out there yet to be found. Eight is enough. (Why does that sound familiar?)
dsylvan
2 / 5 (4) Sep 08, 2018
"And it would leave out the second-most complex, interesting planet in our solar system." --Metzger

The pro-Pluto-as-planet crowd here are demonstrating a lot of confirmation bias. The whole point of coming up with a definition of 'planet' is so we don't have to rely on what we want to be true.
dsylvan
1 / 5 (3) Sep 08, 2018
I'm with Anonym4... in that a dwarf planet is a kind of PLANET. So simple and useful. But I can see how some people who love Pluto would dislike the qualifier 'dwarf'. How about 'smallish' instead?
Mark Thomas
3.6 / 5 (5) Sep 08, 2018
There are a number of objects, not visible to the naked eye and impossible for the backyard astronomer to find, that are larger than Pluto.


That is pure speculation, nothing like that beyond Neptune in our solar system has been found.
flashgordon
1 / 5 (2) Sep 08, 2018
Let's try this again,

The fact that researchers a few hundred years ago don't use the clearing of the path definition of a planet is not a logical deduction.

I was struck that Philip Metzger pointed out "what defined a planet from an asteroid?" I this is the right question. And the answer is partly that of sphericity. But, I've been arguing that what distinguishes a planet from an asteroid is that of element differentiation. The heavy elements diffuse to the core, surrounding the spherical surface of lighter elements.

I wrote a blog entry about it awhile ago. I've shared it with Mike Brown. He pointed out some rather obscure asteroid, which didn't really disprove my definition. i forget which, and that twitter account got shut down(I have a bad habit of getting twitter accounts closed. I really don't believe they were justified in shutting them down.)

http://wwwscienti...day.html

Read more at: https://phys.org/...html#jCp
dsylvan
2.3 / 5 (6) Sep 08, 2018
And while we're at it... as 'planet', or something like it, originally meant 'wanderer', but that describes everything in space, we could call stars 'sizzle planets', white dwarfs 'mini-sizzle planets', old red giants 'fizzle planets', neutron stars 'pit planets', and black holes 'no planets'. We already have our 'rocky', 'ice', 'gas', 'dwarf', 'hot jupiter', and 'super earth' planets, but we could call asteroids 'crumb planets' and long-term comets 'whiz planets'. We could.
Gigel
1 / 5 (4) Sep 08, 2018
@dsylvan: That won't work as intended. People like short terms, so we'll end up with sizzles, fizzles, crumbs, whizzes and catfood all over the place. 'Hubble whiz' and 'the crumb that killed the giant chicken' sounds pretty menacing though.

Side note: that crumb that killed the dinosaurs... didn't just kill them. If there were any around the place of impact, they were probably turned into soup. And then the soup splashed all around the place. It must have been quite good for the little furry critters back then.

Side side note: that giant chicken soup would be a great business idea if one gets a time machine...
maholmes1
1 / 5 (2) Sep 09, 2018
Well, then Eris ("Xena") must also be a planet.


Yes. Exactly.
maholmes1
3.7 / 5 (6) Sep 09, 2018
It is estimated that there are 200 dwarf planets similar to Pluto in the Kuiper belt, and possibly more than 10,000 in the region beyond. So if you want to keep Pluto a planet, then there will inevitably be thousands of planets in the solar system. .


Nobody's talking about undesignating the smaller moons of Jupiter and Saturn as not real moons because there are so many of them that you need to consult a table unless you have a real good memory. Nobody's talking about declaring that red dwarf stars are not real stars, or saying that dwarf galaxies are not real galaxies, or in fact artificially limiting the number of rivers and mountains on Earth. The solar system or any other star system has however many planets it has. There aren't actually that many dwarf planets of Sol known and if there turn out to be 1000 objects that fit the geophysical definition of planet,then the Sun has 1000 planets, Just learn what a planet or galaxy or river is instead of memorizing names.
arcmetal
3.7 / 5 (3) Sep 09, 2018
@maholmes1
It is estimated that there are 200 dwarf planets similar to Pluto in the Kuiper belt, and possibly more than 10,000 in the region beyond. So if you want to keep Pluto a planet, then there will inevitably be thousands of planets in the solar system. .


... and if there turn out to be 1000 objects that fit the geophysical definition of planet,then the Sun has 1000 planets, Just learn what a planet or galaxy or river is instead of memorizing names.

You are making too much sense. It takes time for others to see the obvious.
maholmes1
2.3 / 5 (3) Sep 09, 2018
"And it would leave out the second-most complex, interesting planet in our solar system." --Metzger

... The whole point of coming up with a definition of 'planet' is so we don't have to rely on what we want to be true.


Exactly. And the geophysical definition is nice and simple and logical.
TheGhostofOtto1923
3 / 5 (4) Sep 09, 2018
Hey I know - how about 'plutonian planetoid'? Class occupancy currently 1.
Parsec
4 / 5 (4) Sep 10, 2018
There are subtleties at work here
The people who designated Planet Pluto not a planet have clearly to go back and study Sir Isaac Newton's Gravity, because they clearly do not understand its subtleties
Old_C_Code> Gran: the moon orbits Earth, they are not in a binary orbit.

The moon orbits the earth, where as the earth orbits the moon - the earth attracts the moon, where as the moon attracts the earth - earth's gravity attracts the moon, where as the moons gravity attracts the earth.
To realise this subtlety, if the earth's gravity was neutralised, the earth would continue orbiting the moon.

Read more at: https://phys.org/...html#jCp

All bodies which "orbit" each other actually orbit a common center of gravity. In this sense, nothing actually "orbits" each other. But if earth'c gravity was 0 (neutralized) all centers of gravity that included the earth would cease to exist, and the earth would simply be ejected into interstellar space.
Jonseer
3 / 5 (2) Sep 10, 2018
He is not making a good example of a scientist. He tries to game the language in making his argument.

The definition does not literally require a planet to be the only object in its orbit.

It requires that it be overwhelmingly dominant as is Earth, which has a moon that shares its orbit but is not considered a planet, because it's under the gravitational control of Earth.
Jonseer
3 / 5 (2) Sep 10, 2018
To reinforce the current definition of a planet they could additionally define a planet as an object large enough so as not to change its nature regardless of where it orbits in the Solar System.

Pluto if put in the orbit of Mercury would basically evaporate. None of the 8 planets would change that much in the same situation. They'd be able to maintain their mass regardless of whatever surface changes that would occur so close to the sun.

Mercury in Pluto's orbit would be able to gather and keep an atmosphere, but also remain unchanged essentially.

Pluto is made of frozen gases can't survive anywhere closer than the Orbit of Uranus.
jpdemers
2.3 / 5 (3) Sep 10, 2018
In the past 200 years only one publication used the clearing-orbit requirement to classify planets... and... so what???
If the whole point is to come up with a new and more useful definition, what does it matter what the definition was 200 years ago? This "research" only proves that the new definition is ... wait for it ... new.
granville583762
3 / 5 (6) Sep 10, 2018
Welcome to planet Dwarf and its Dwarflings

The earth has not cleared its orbit as the moon is slowly leaving the earth in ever increasing circles - So it is the moon that is clearing its orbit, as the earth has not cleared its orbit, as under the strict criteria of clearing ones orbit, earth no longer qualifies as a member of the full planet status club.

We are no longer earthlings, as we are re-designated under the I.S.U rules as we are now Dwarflings!
The I.S.U is working on a protocol to streamline the re-designation and designate earth's status in line with its dwarf status so now planet earth is now re-designated as planet Dwarth!
laurele
2.6 / 5 (5) Sep 10, 2018
This whole dispute is over nomenclature rather than basic scientific principles. Furthermore, both sides have good points, and I don't have a problem either way. I'm happy with calling Pluto a "dwarf planet" as distinct from a "major planet".


The problem with this proposal is it sets up a false dichotomy in which anything not classed as a major planet is considered a minor planet. This is misleading because the term "minor planet" is used to refer to objects not large enough to be rounded by their own gravity--asteroids and comets. Dwarf planets are not minor planets because they are in hydrostatic equilibrium. A better option is to get rid of the terms major and minor planet and instead use the term "planet" as a broad umbrella under which there are subclasses such as terrestrials, jovians, and dwarf planets.
laurele
2.6 / 5 (5) Sep 10, 2018
Give it up, find something useful to research; if you are capable? Are you Pluto's attorney?

The world is full of regressors, royalists, etc.

And Pluto is TINY too. As ShotmanMaslo says, there may be hundreds of Plutos.
Cool alcohol collection nevertheless!

Telling people to "give up" on something they believe in and accept a flawed definition is insulting. Pluto is not that tiny. It is large enough to be in hydrostatic equilibrium, rounded by its own gravity. That, according to the equally scientific geophysical planet definition, makes it a planet. So what if there are many, even hundreds, of planets in the solar system? There is no scientific merit to the argument that we cannot have "too many planets." And there is no need for kids to memorize a list of names to learn about the solar system. That is an archaic teaching method dating back to the time we knew little else about the planets other than their names.
laurele
3 / 5 (6) Sep 10, 2018
There are a number of objects, not visible to the naked eye and impossible for the backyard astronomer to find, that are larger than Pluto. They too would have to be classified as planets. There may be something outside even Pluto's orbit, but still orbits the sun. It too would have to be a planet. There may be additional objects out there yet to be found. Eight is enough. (Why does that sound familiar?)

To date, no objects larger than Pluto have been discovered in the outer solar system. And any object brought close enough to its parent star would begin outgassing and eventually lose its atmosphere. This is happening to some giant exoplanets in close orbits around their stars.Pluto is not made of frozen gases, as its composition is 70 percent rock.
Anonym644134
1 / 5 (1) Sep 12, 2018
Don't use emotion over reason. Use the Sesame Street test: 1 of these is not like the others.

Planets are:

1. at increasing intervals from the sun (m,v,e,m,j,s,u,n)
2. do not cross another orbit (m,v,e,m,j,s,u,n)
3. generally circular in orbit (m,v,e,m,j,s,u,n)
4. within 7.5 degrees of Earth's ecliptic plane(m,v,m,j,s,u,n)

Pluto fails all 4. A five-year-old can figure this out.
maholmes1
3 / 5 (2) Sep 12, 2018

Pluto if put in the orbit of Mercury would basically evaporate. None of the 8 planets.


Geophysically, 13 and counting. Just saying.
maholmes1
2.3 / 5 (3) Sep 12, 2018
Don't use emotion over reason. Use the Sesame Street test: 1 of these is not like the others.

Planets are:

1. at increasing intervals from the sun (m,v,e,m,j,s,u,n)
2. do not cross another orbit (m,v,e,m,j,s,u,n)
3. generally circular in orbit (m,v,e,m,j,s,u,n)
4. within 7.5 degrees of Earth's ecliptic plane(m,v,m,j,s,u,n)

Pluto fails all 4. A five-year-old can figure this out.


Setting aside your ad hominem attack on supporters of Pluto's planethood for a second and also assuming you're not being ironic: Why would an object have to have a circular orbit on or near the ecliptic that doesn't cross the orbit of another planet, in order to be a planet? This reminds me of the Catholic Church insisting to Galileo that there were no sunspots because the heavens were perfect.
Anonym590659
1 / 5 (1) Sep 12, 2018
This (large radius, massive, one per orbit, all orbits sharing a single plane) is the model of a planetary system that could be searched for (automatically) by the Kepler space telescope.

Reclassifying Pluto as something other than a "planet" was a practical way to maintain international relevance (to the top of Google search) in expectation of major discoveries and broad public excitement. And then the first images of boring ice-ball Pluto arrived...
My Very Educated Mother Just Served Us 9 Pizza-pies.

Plato would approve of Geophysical definition. Aristotle...? Not so sure.
Mark Thomas
3 / 5 (3) Sep 12, 2018
Use the Sesame Street test: 1 of these is not like the others.


LOL! The problem is in your math. Instead of 1, it is more like a trillion, trillion planets in the universe are not like the 8 better known planets in our own solar system. Another pre-school lesson for you, i.e., object permanence, which would hold a planet is a planet, regardless if you can see it and regardless of its location. Orbit is irrelevant.

I like this definition better: A planet is a sub-stellar, celestial body at least 2,000 kilometers in diameter.
maholmes1
2.3 / 5 (3) Sep 12, 2018
Use the Sesame Street test: 1 of these is not like the others.


LOL! The problem is in your math. Instead of 1, it is more like a trillion, trillion planets in the universe are not like the 8 better known planets in our own solar system. Another pre-school lesson for you, i.e., object permanence, which would hold a planet is a planet, regardless if you can see it and regardless of its location. Orbit is irrelevant.

I like this definition better: A planet is a sub-stellar, celestial body at least 2,000 kilometers in diameter.


At 2000 kilometers in diameter it would be able to hold on to an atmosphere dense enough to have weather, two more things associated with planethood. Ceres doesn't have the gravity to do that. Pluto does.
maholmes1
2.3 / 5 (3) Sep 12, 2018
This (large radius, massive, one per orbit, all orbits sharing a single plane) is the model of a planetary system that could be searched for (automatically) by the Kepler space telescope.

Reclassifying Pluto as something other than a "planet" was a practical way to maintain international relevance (to the top of Google search) in expectation of major discoveries and broad public excitement. And then the first images of boring ice-ball Pluto arrived...
My Very Educated Mother Just Served Us 9 Pizza-pies.


My Very Educated Mother Cannot Just Serve Us Nine Pizzas--Hundreds May Eat. A planet is a planet, and there aren't nine anymore; there are at least 13, just orbiting Sol, never mind all the exoplanets out there.

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