'); }
ILLUSTRATION IS RESERVED - DO NOT USE. The eight planets of the Solar System and the dwarf planet Pluto. For many astronomers and planetary scientists Pluto's status remains an open question. Redefining what is a planet could return Pluto to the fold - 9 planets and also open the door for many more. Insets from upper left, clockwise: Clyde Tombaugh, Mike Brown, Alan Stern, Gerard Kuiper.(Credit: NASA, Judy Schmidt, Björn Jónsson)

A Recipe for Returning Pluto to Full Planethood

Article Updated: 23 Dec , 2015

by

A storm is brewing, a battle of words and a war of the worlds. The Earth is not at risk. It is mostly a civil dispute, but it has the potential to influence the path of careers. In 2014, a Harvard led debate was undertaken on the question: Is Pluto a planet. The impact of the definition of planet and everything else is far reaching – to the ends of the Universe.

It could mean a count of trillions of planets in our galaxy alone or it means leaving the planet Pluto out of the count – designation, just a dwarf planet. This is a question of how to classify non-stellar objects. What is a planet, asteroid, comet, planetoid or dwarf planet? Does our Solar System have 8 planets or some other number? Even the count of planets in our Milky Way galaxy is at stake.

"Dawn arising." The latest image of Ceres - February 12, 2015 -  by the Dawn spacecraft from 80,000 km. With icy deposits pock marking its surface, a possible reservoir of water below its surface, is Ceres a planet, dwarf planet, an asteroid or all three? (Credit: NASA/Dawn)

“Dawn arising.” The latest image of Ceres – February 12, 2015 – by the Dawn spacecraft from 80,000 km. With icy deposits pock marking its surface, a possible reservoir of water below its surface, is Ceres a planet, dwarf planet, an asteroid or all three? (Credit: NASA/Dawn)

Not to dwell on the Harvard debate, let it be known that if given their way, the debates outcome would reset the Solar System to nine planets. For over eight years, the solar system has had eight planets. During the period  1807 to 1845, our Solar System had eleven planets. Neptune was discovered in 1846 and astronomers began to discover many more asteroids. They were eliminated from the club. This is very similar to what is now happening to Pluto-like objects – Plutoids. So from 1846 to 1930, there were 8 planets – the ones as defined today.

The discoverer of Pluto - Clyde Tombaugh in the 1930s and again with homebuilt telescope in the 1990s that earned him an assignment at Lowell Observatory - discover Planet X. Cremated remains of Clyde are attached to the New Horizons space probe now approaching the dwarf planet Pluto.

The discoverer of Pluto – Clyde Tombaugh in the 1930s and again with homebuilt telescope in the 1990s that earned him an assignment at Lowell Observatory – discover Planet X. The cremated remains of Clyde are attached to the New Horizons space probe that is now approaching the dwarf planet Pluto.

In 1930, a Kansas farm boy, Clyde Tombaugh, hired by Lowell Observatory discovered Pluto and for 76 years there were 9 planets. In the year 2006, the International Astronomical Union (IAU) took up a debate using a “democratic process” to accept a new definition of planet, define a new type – dwarf planet and then set everything else as “Small Bodies.” If your head is spinning with planets, you are not alone.

All two body systems have a barycenter, the shared point in space around which they orbit. Pluto and Charon’s happens to be between both bodies due to their proximity and similar mass. (Credit: NASA/New Horizons)

Two NASA missions were launched immediately before and after the IAU announcement took affect. The Dawn mission suddenly was to be launched to an asteroid and a dwarf planet and the New Horizons had rather embarked on a nine year journey to a planet belittled to a dwarf planet – Pluto. Principal Investigator, Dr. Alan Stern was upset. Furthermore, from the discoveries of the Kuiper mission and other discoveries, we now know that there are hundreds of billions of planets in our Milky Way galaxy; possibly trillions. The present definition excludes hundreds of billions of bodies from planethood status.

The presently known largest trans-Neptunian objects (TSO) - are likely to be surpassed by future discoveries. Which of these trans-Neptunian objects (TSO) would you call planets and which "dwarf planets"? (Illustration Credit: Larry McNish, Data: M.Brown)

The presently known largest trans-Neptunian objects (TSO) – are likely to be surpassed by future discoveries. Which of these trans-Neptunian objects (TSO) would you call planets and which “dwarf planets”? (Illustration Credit: Larry McNish, Data: M.Brown)

There are two main camps with de facto leaders. One camp has Dr. Mike Brown of Caltech and the other, Dr. Stern of the Southwest Research Institute (SWRI) as leading figures. A primary focus of Dr. Brown’s research is the study of trans-Neptunian objects while Dr. Sterns’s activities are many but specifically, the New Horizons mission which is 6 months away from its flyby of Pluto. Consider first the IAU Resolution 5A that its members approved:

(1) A “planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.

(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects, except satellites, orbiting the Sun shall be referred to collectively as “Small Solar System Bodies”.

This is our starting point – planet, dwarf planet, everything else. Consider “everything else”. This broad category includes meteoroids, asteroids, comets and planetesimals. Perhaps other small body types will arise as we look more closely at the Universe. Within the category, there is now a question of what is an asteroid and what is a comet. NASA’s flybys of comets and now ESA’s Rosetta at 67P/Churyumov–Gerasimenko are making the delineation between the two types difficult. The difference between a meteoroid and an asteroid is simply defined as less than or greater than one meter in size, respectively. So the Chelyabinsk event absolutely involved a small asteroid – about 20 meters in diameter. Planetesimals are small bodies in a solar nebula that are the building blocks of planets but they could lead to the creation of all the other types of small bodies.

Dr. Alan Stern, project scientist for New Horizons and Neil deGrasse Tyson discuss the New Horizons spacecraft in the mission operations center at JHU/APL. The interview was for a NOVA special (12/14/2011), the Pluto Files, about a Kansas farm boy, a missing planet and the 70 years of astronomical discoveries leading to the present day. (Credit: JHU/APL,PBS)

Dr. Alan Stern, project scientist for New Horizons and Neil deGrasse Tyson discuss the New Horizons spacecraft in the mission operations center at JHU/APL. The interview was for a NOVA special (12/14/2011), the Pluto Files, about a Kansas farm boy, a missing planet and the 70 years of astronomical discoveries leading to the present day. (Credit: JHU/APL,PBS)

Putting aside the question of “Small Bodies” and its sub-classes, what should be the definition of planet and dwarf planet? These are the two terms that demoted Pluto and raised Ceres to dwarf planet. It is also interesting to note how Resolution 5A is meant exclusively for our Solar System. In 2006, there were not thousands of exo-planets but just a few dozen extreme cases but nevertheless, the IAU did not choose to extend the definition to “stars” but rather just in reference to our pretty well known star, the Sun.

Recall Tim Allen’s movie, “The Santa Clause”. Clauses can cause a heap of trouble. The IAU has such a clause – Clause C which has caused much of the present controversy around the definition of planets. Clause (c) of Resolution 5A: “has cleared the neighborhood around its orbit.” This is the Pluto killer-clause which demoted it to dwarf planet status and reduced the number of planets in our solar system to eight. In a sense, the IAU chose to cauterize a wound, a weakness in the definitions, that if left unchanged, would have led to who knows how many planets in our Solar System.

The question of what is Pluto is open for public discussion so armed with enough knowledge to be dangerous, the following is my proposed alternative to the IAU’s that are arguably an improvement. The present challenge to Pluto’s status lies in the Kuiper Belt and Oort Cloud. Such belts or clouds are probably not uncommon throughout the galaxy. Plutoids are the 500 lb gorilla in the room.

Two spacecraft, Dawn and New Horizon will reach their final objectives in 2015 - Dwarf Planets - Ceres and Pluto. (Credit: NASA, Illustration - T.Reyes)

Two spacecraft, Dawn and New Horizon will reach their final objectives in 2015 – Dwarf Planets – Ceres and Pluto. (Credit: NASA, Illustration – T.Reyes)

This year, as touted by the likes of Planetary Society, Universe Today and elsewhere, is the year of the dwarf planet. How remarkable and surprising will the study of Ceres, Pluto and Charon by NASA spacecraft be? There is a strong possibility that after the celestial dust clears and data analysis is published, the IAU will take on the challenge again to better define what is a planet and everything else. It is impossible to imagine that the definitions can remain unchanged for long. Even now, there is sufficient information to independently assess the definitions and weigh in on the approaching debate. Anyone or any group – from grade schools to astronomical societies – can take on the challenge.

To encourage a debate and educate the public on the incredible universe that space probes and advanced telescopes are revealing, what follows is one proposed solution to what is a planet and everything else.

planet: is a celestial body that a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium – nearly round shape, b) has a differentiated interior as a result of its formation c) has insufficient mass to fuse hydrogen in its core, d) does not match the definition of a moon.

minor planet: is a planet with a mass less than one Pluto mass and does not match the definition of a moon.

inter-Stellar (minor) planet: is a (minor) planet that is not gravitationally bound to a stellar object.

binary (minor) planet: is a celestial body that is orbiting another (minor) planet for which the system’s barycenter resides above the surface of both bodies.

These definitions solve some hairy dilemmas. For one, planets orbit around the majority of most stars in the Universe, not just the Sun as Resolution 5A was only intended. Planets can also exist gravitationally not bound to a star –  the result of it own molecular cloud collapse without a star or expulsion from a stellar system. One could specify gravitational expulsion however, it is possible that explosive events occur that cause the disintegration of a star and its binding gravity or creates such an impulse that a planet is thrusted out of a stellar system. Having an atmosphere certainly doesn’t work. Astronomers are already anticipating Mars or Earth-sized objects deep in the Oort cloud that could have no atmosphere – frozen out and also despite their size, not be able to “clear their neighborhood.”

An animation (above) of Kepler mission planet candidates compiled by Jeff Thorpe. Kepler and other exoplanet projects are revealing that the properties of planets – orbits, size, temperature, makeup – are all extreme. Does Pluto represent one of those extremes – the smallest of planets? (Credit: NASA/Kepler, Jeff Thorp)

 

The need to create a lower-end limit to what is a planet reached a near fever pitch with the discovery of a Trans-Nepturnian Object (TNO) in 2005 that is bigger than Pluto – Eris.  Dr. Michael Brown of Caltech and his team led in the discovery of bright large KBOs. There was not just Eris but many of nearly the same size as Pluto. So without clause (c), one would be left with a definition for planet that could allow the count of planets in our Solar System to rise into the hundreds maybe even thousands. This would become a rather unmanageable problem; the number of planets rising year after year and never settled and with no means to make reasonable comparisons between planetary systems throughout our galaxy and even the Universe.

The book that tells the story of discovery - trans-Neptunian objects (TNO) that led to the downfall of Pluto from full planethood to that of a dwarf. The 2006 IAU decision was a pre-emptive strike to stave off a proliferation of planets in our system. It worked but "killed" Pluto. Did it have it coming? Dr. Brown also agrees that the present definition of planet is flawed and incomplete. (Photo Credits: Caltech/M.Brown)

The book that tells the story of discovery – trans-Neptunian objects (TNO) that led to the downfall of Pluto from full planethood to that of a dwarf. The 2006 IAU decision was a pre-emptive strike to stave off a proliferation of planets in our system. It worked but “killed” Pluto. Did it have it coming? Dr. Brown also agrees that the present definition of planet is flawed and incomplete. (Photo Credits: Caltech/M.Brown)

Two more celestial body types follow that are proposed to round out the set.

moon: is a celestial body that a) orbits a (minor) planet and b) for which the barycenter of its orbit is below the surface of its parent (minor) planet.

This creates the possibility of a planet-moon system such that its barycenter is above the surface of the larger body. Pluto and Charon are the most prominent case in our Solar System. In such cases, if one body meets the criteria of a (minor)planet, then the other body can also be assessed to determine if it is also a (minor) planet and the pair as binary (minor) planets. If the primary body was a minor planet, it is possible that the barycenter could be above its surface but the secondary body does not meet all the criteria of a minor planet, specifically “differentiated interior”.

The definition of moon is compounded by the existence of, for example, asteroids with moons. For such objects, the smaller object is defined as a satellite.

Satellite: is a celestial body that a) orbits another celestial body, b) whose parent body is not a (minor) planet.

Another permissible term is moonlet which could be used to describe both very small moons such as those found in the Jovian and Saturn systems or a small body orbiting an asteroid or comet. Moonlet could replace satellite.

The discriminator between planet and moon is not mass but simply whether the celestial body orbits a (minor) planet and the barycenter resides inside the larger body. The definition of moon excludes the possibility of a planet orbiting another planet except in the special case of binary (minor) planet.

Defining a lower size limit to “Planet” is necessary to compare stellar systems and classify. A limit based on the body’s average surface pressure and temperature or the surface gravity could define a limit. While they could, they are not practical because of the extremes and diverse combinations of conditions. Strange objects would fall through the cracks.

Removing clause (c) – “has cleared the neighborhood around its orbit” – will avoid a future conflict such as a very low mass star with a plutoid-sized object or smaller, in a close orbit that has cleared its neighborhood.

Additionally, choosing to declare that Pluto becomes the “standard weight” that differentiates minor planet from planet sets a precedent. In an era in which computers measure and tally the state of our existence, setting this limit to include Pluto and return it as the ninth planet of our Solar System, is, in a small but significant way, a re-declaration of our humanity. Soon we will be challenged by artificial intelligence greater than ours; we are already have. Where will we stand our ground?

Forget about Pluto for a moment. Should Eris be our tenth Planet? Like Pluto it has a prominent moon- Dysnomia. Human perception and conceptions of the Universe have shaped our view of the Solar System. The Ptolemaic system (Earth centered), Kepler's Harmonic Spheres, even the fact that ten digits reside on our hands impact our impression of the Solar System (Photo Credits:NASA/ESA and M. Brown / Caltech)

Forget about Pluto for a moment. Should Eris be our tenth planet? Like Pluto it has a prominent moon- Dysnomia. Human perception and conceptions of the Universe have shaped our view of the Solar System. The Ptolemaic system (Earth centered), Kepler’s Harmonic Spheres, even the fact that ten digits reside on our hands impact our impression of the Solar System (Photo Credits:NASA/ESA and M. Brown / Caltech)

The consequences of this proposed set of definitions, makes Ceres a minor planet and no longer an asteroid. Many trans-Neptunian objects discovered in this century become minor planets. Of the known TNOs only Pluto and Eris meets the criteria of planet.The dwarf planet Eris would become the tenth planet. Makemake, Sedna, Quaoar, Orcus, Haumea would be minor planets. By keeping Pluto a planet and defining it as the standard bearer, only one new planet must be declared. Surely, more will be found, very distant, in odd elliptical and tilted orbits. The count of planets in our solar system could rise by 10, 20 maybe 50 and perhaps this would make the definition untenable but maybe not. So be it. New Horizons will fly by a dwarf planet in July but this should mark the beginning of the end of the present set of definitions.

Three perspectives of a ten planet Solar System. No longer Earth centered, or with harmonic spheres but now with planets outside the ecliptic plane and growing. How many planets would be too many? (Credits: Wikimedia, T.Reyes)

Three perspectives of a ten planet Solar System. No longer Earth centered, or with harmonic spheres but now with planets outside the ecliptic plane and growing. How many planets would be too many? (Credits: Wikimedia, T.Reyes)

This set of definitions defines a set of celestial bodies that consistently covers the spectrum of known bodies. There is the potential of exotic celestial objects that are spawned from cataclysmic events or from the unique conditions during the early epochs of the Universe or from remnants of old or dying stellar objects. Their discovery will likely trigger new or revised definitions but these definitions are a good working set for the time being. Ultimately, it is the decision of the IAU but the sharing of knowledge and the democratic processes that we cherish permits anyone to question and evaluate such definitions or proclamations.To all that share an interest in Pluto as or as not a planet raise your hand and be heard.

A video from 2014 by Kurz Gesagt describing the Pluto-Charon system. Is this a binary planet system or one of the “dwarf” variety?

Further Reading

Learn All About Pluto, The Most Famous Dwarf Planet, E. Howell, Universe Today, 1/17/2015

A synopsis of Pluto facts and figures at Universe Today, compendium of pages on Pluto

What is the Kuiper Belt?, video, Universe Today, 12/30/2013, Fraser Cain asks Mike Brown to explain the Kuiper Belt

Is The Moon A Planet?, E. Howell, Universe Today, 1/27/2015

It Looks Like These Are All the Bright Kuiper Belt Objects We’ll Ever FindUniverse Today, 1/12/2015

2015, NASA’s Year of the Dwarf Planet, Universe Today, 12/14/2014

A Serendipitous All Sky Survey For Bright Objects In The Outer Solar SystemCornell University Library, 1/5/2015

Ten Years of Eris, at Mike Brown’s Planets, 1/5/2015

My condolences to the friends and family of Tammy Plotner, the first regular contributing writer to Universe Today. Can’t we all relate to what drew Tammy to write about the Universe? She wrote outstanding articles for U.T.

me_and_the_dob

'); }

, , , , , , , , , ,



Sort by:   newest | oldest | most voted
Zoutsteen
Member
Zoutsteen
February 19, 2015 7:33 PM

How about:
What would the atmoshperic composition be at Goldilocks distance.

Although, I liked the kinetic mass balance equation a bit more.
If you smashed the Moon into Earth gives different result than if you smashed Charon into Pluto.
Earth2* would be left afterwards, but no Pluto2.

*(Plus lots of rubble ofc)

laurele
Member
February 19, 2015 8:13 PM
There are several resources that should be added to your list: The Case for Pluto, a book by Alan Boyle: http://www.amazon.com/The-Case-Pluto-Little-Difference/dp/0470505443 Is Pluto A Planet? a book by Dr. David Weintraub: http://press.princeton.edu/titles/8247.html Pluto Confidential, a book by Laurence A. Marschall. who voted for the IAU decision, and Steve Maran, who opposes it: http://www.amazon.com/Pluto-Confidential-Insider-Account-Ongoing/dp/1933771801 “Responding to the IAU: Pluto and the Developing Landscape of the Solar System,” Laurel’s Pluto Blog: http://laurelsplutoblog.blogspot.com/2013/02/responding-to-iau-pluto-and-developing.html I will raise several points in response to your discussion. Essentially, your planet definition is the same as that proposed by Dr. Ken Croswell, who argues for setting the minimum threshold for planethood at the mass and size of Pluto. http://www.kencroswell.com/NinthRockFromTheSun.html While removing the “requirement” that an object… Read more »
Pasander
Member
Pasander
February 19, 2015 9:05 PM

I feel that Pluto is not a “proper” planet. Pluto-Charon is too much different from the “real” planets. And it doesn’t dominate.

Then again, if an Earth-sized world was found orbiting Sun farther out, I would probably call it a planet, even if it hadn’t (yet) “cleared its neighborhood” and had a tilted non-circular orbit.

laurele
Member
February 19, 2015 9:32 PM

What makes something a “proper planet?” Both Pluto and Charon have the same processes and structures as their larger counterparts. The only difference is they are smaller.

Many giant exoplanets have orbits around their stars that are far more elliptical than Plutos. If an elliptical orbit precludes an object from being a planet, what then are these objects?

Why should dominating its orbit be a requirement for planethood? Such a requirement is inherently biased against objects further from their parent stars, which have larger and larger orbits to clear. Planets should be defined by their intrinsic properties, not by their locations.

Kevin Heider
Member
Kevin Heider
February 19, 2015 9:24 PM

So basically they want to claim anything as massive as Pluto is a planet? Yuck, what do you do with the countless objects that will be discovered where we simply do not know if an object has a diameter comparable to Pluto much-less that the object is more massive than Pluto? You are just trading one arbitrary solution for another. Leave well enough alone.

Beckler
Member
Beckler
February 19, 2015 9:56 PM

I dunno. I admit to not reading the full article because this debate has never been interesting to me. The solar system is what it is and we should study it, but explain to me how this is any more than semantics? Who cares one way or the other?

FarAwayLongAgo
Member
FarAwayLongAgo
February 19, 2015 10:06 PM
This is a battle which cannot be won. How long is a piece of string? I imagine how someone at that infamous IAU meeting asked: “What is a planet, really?” And he got the embarrassing answer: “We don’t know. Oops, let’s make something up and vote about it so that the public doesn’t get the impression that we don’t know what we are talking about!” And from there on. What a planet is, is culturally defined. The week has seven days, one for each of the planets. Including the Sun and the Moon, but not Earth because it wasn’t until the 17th century that it was discovered that the Earth is a planet. Voting or defining by some… Read more »
Jeffrey Boerst
Member
February 20, 2015 3:29 AM
“Voting or defining by some astronomer at some meeting doesn’t change this. They should keep to their astronomy instead of making fools of themselves.” … Erm… I’m REALLY curious about how you think that Astronomers attempting to add a new and clearly necessary iteration to a measuring system specific to their discipline would be NOT sticking to their astronomy… This is clearly no different than when geologists chiseled the list of how the different sizes and types of rocks would be labeled, when physicists were breaking down their categorization of the particle world and biologists were dissecting the veritable zoo of cellular structures. The implication of your snide venom is obviously flawed… Maybe consider WHAT you’re saying more… Read more »
FarAwayLongAgo
Member
FarAwayLongAgo
February 20, 2015 7:42 AM

Do any exoplanets exist? Or are they maybe exodwarfplanets? Is a hot super-Jupiter which has not cleared its orbit a “dwarf planet”? By the way, how useful is a categorization of objects which includes both Mercury and Saturn? You could study Titan or Ceres up close and still have no idea how IAU classifies it.

The IAU should not have messed with this. They unfortunately tried, and they failed miserably and became everyone’s laughing stock. Or do you have a definition of how long a piece of string is?

(I politely ignore your OT trolling attacks on me personally.)

astrofan
Member
astrofan
February 19, 2015 10:26 PM
Good to see someone take a more comprehensive “look” at this issue.. While the author tries to address “all” issues.. the article could have been more “fair and balanced”.. #1: The IAU’s “democratic” voting should have been more elaborated.. ie: just 4% of the membership voting on the last hour is sorta ramrodding a “special interest” viewpoint.. Well documented.. #2: The author should not only mention Brown’s book but also mention Alan Boyle’s book.. The pictorial display of Brown’s book can be construed as an ad for it.. the more fair balanced approach is just mention both books.. or pictorially display Boyle’s book too. #3: Asking for a public debate between Neil DeGrasse & Alan Stern would have… Read more »
Jeffrey Boerst
Member
February 20, 2015 3:39 AM
“…we US citizens quite easily remember 50 States” Unless you’re over the age of 65 or a geek, I’m afraid that more Americans than not aren’t even aware of which is North and which, South… between Canada and Mexico, save all 50 states names. This has been tested. “The definition of a minor planet “below a mass” of a certain planet cries the need for a new definition which is not “name” specific. A Chihuahua and St. Bernard are both dogs..” It’s simply a case of a science suddenly discovering many more of a certain type of thing (in our Solar System and others), which forces the need to add classification terms to make organizing the data easier.… Read more »
EarthlingX
Member
February 19, 2015 11:16 PM

Of course they are all planets and there is nothing wrong with finding more of them. Beyond silly ..
I don’t think using Pluto’s size as a standard planetary margin is such a great idea though. It should be something from basic physics and not based on one example.

Jeffrey Boerst
Member
February 20, 2015 3:51 AM
Did you see the infographic in this article representing the largest of the even more populous list of known Dwarf Planets? There alone are ten, not one, not even counting those objects’ satellites. And one is even larger than Pluto. That’s the whole point. More and more of these objects, let alone planet types per extra solars, are being discovered every day and because of this, Astronomy’s data classification system is on the verge of getting VERY cluttered and disorganized. It’s like why there are “silt”, “sand” “pebbles”, “rocks”, “boulders”, etc. and all relegated to specific size ranges, in geology. All the sciences do this to make it easier to be specific when they communicate within their ranks… Read more »
EarthlingX
Member
February 20, 2015 4:12 AM

This story is more about Ceres than Pluto and about organizing things based on actual knowledge and methods.
It’s just that it seems that public sentiment, mine included for a change, which defines how words are used, puts more emphasis on planet being round and orbiting a star, than it’s housekeeping manners.
Or in other words, they are all planets : dwarves, proto, giants, gaseous, rocky : if it’s round and orbits a star – planet, simple.
If you feel you need more precise definitions, figure out which gas is most prone to gravitational collapse, and calculate it’s mass when it gets round with no rotation.
That should work anywhere.

Jeffrey Boerst
Member
February 20, 2015 5:26 AM

I dig the public sentiment thing and as far as that goes, whatever anyone wants to call the things in common conversation is all well and good. I was commenting much more on the comments about why the scientists are debating this than on the story itself. What I said was the actual reason Astronomers are going through this process as has been asked and wondered about and commented on in this thread.

Astrostevo
Member
Astrostevo
February 20, 2015 5:22 AM
The first definition – a planet : “.. is a celestial body that a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium – nearly round shape, b) has a differentiated interior as a result of its formation c) has insufficient mass to fuse hydrogen in its core, d) does not match the definition of a moon.” Is absolutely spot on right to me. There are many types of planet ranging from gas giants like Jupiter though to planets like Earth and also planets like Pluto. A dwarf star is still a star and a dwarf planet is still a planet just as a dwarf person is still a… Read more »
EarthlingX
Member
February 20, 2015 9:36 AM

Agreed, on all points.

Mich48
Member
Mich48
February 20, 2015 12:49 AM
Saying dwarf planet seems to be very subjective. It is still a planet as the Inclusion of the name planet is still in the name dwarf planet. To me that means Pluto is a planet! Just as a person referred to as dwarf does not mean that they are not a person. We love to label and categorize so much. If such a small world was in the goldilocks zone and had intelligent life how could we justify saying it is not a “real” planet. Given enough atmosphere with the right elements any decent moon with a comfortable temperature could support life. Are we not speculating life on the moons of Jupiter. Somewhere that supports life would be… Read more »
Chris Aikman
Member
February 20, 2015 2:09 AM

Back in 2006, right after the reclassification of Pluto as a dwarf planet, I was buying gasoline at a local station. The female attendant noted my “Pluto is the Coolest Planet” tee shirt, expressed her fierce disapproval of what had transpired with Pluto, and then growled “There will be consequences for this!”

She was right. People love Pluto. Don’t mess with it!

Tony Mach
Member
Tony Mach
February 20, 2015 5:12 AM
Sorry, but this proposal is a piece of cr*p. Why the heck would anyone choose “one Pluto mass” as the yardstick for anything, except for misguided sentimental reasons??? And why stop there? Why exclude Charon? After all, why should Pluto be a planet, but Charon not? What about the other KBOs? And why not include Ceres and Vesta as planets? Why not include our Moon and the Sun? I’m sure there are people out there still rejecting the heliocentric worldview, should we next hear what they have to say? And why not include planets existing only in the imagination of some people? I’m all for hearing a reasonable attempt to redefine what is and isn’t a planet, but… Read more »
Astrostevo
Member
Astrostevo
February 20, 2015 5:32 AM

@ ^ Tony Mach, Um, didn’t you read the proposed planet definition provided in the article there?

It isn’t just Pluto and it is far superior to the current rather absurd IAU definition. The definition there would add the other ice dwarfs incl. Ceres, Eris , Haumea, Sedna etc .. and I and other supporters of that definition have no problem with that at all.

justin13
Member
justin13
February 20, 2015 2:37 PM

No, the definition suggested in the article would not add the other current dwarf planets- the author clearly states it would only elevate Eris. Making Pluto’s mass the dividing line is an arbitrary and misguided choice.

Astrostevo
Member
Astrostevo
February 20, 2015 5:34 AM

Come on IAU, Pluto is no comet, no asteroid and very much a planet worthy of that title and recognition as such. Pluto has for instance its own weather, more moons than the whole four inner solar system rock dwarfs combined and maybe rings and more as well.

Its time to recognise reality and acknowledge that all dwarf planets (whether icy or rocky – remember Earth couldn’t clear its orbit at Pluto’s distance either!) are planets too every bit as much as their bigger brethren!

Alkaid
Member
Alkaid
February 20, 2015 5:57 AM

“Planet” should be recognized to be an unscientific term but rather a historical term. This should then be understood to include only the nine planets.

Then you either choose another term for the other stuff or use modifiers. So exoplanets, dwarf planets, Oort planets, etc. should be OK.

The Harvard outcome makes more sense than does what a non-quorum of the IAU set up.

Kevin Heider
Member
Kevin Heider
February 21, 2015 12:11 PM

Historically a planet was any object that moved against the background of fixed stars and thus included the Sun and Moon.

Steve Nerlich
Member
February 20, 2015 6:55 AM

Elephant in the room: Haumea.

While it’s not actually spherical, it is low mass, so if you do a bit of hand-waving, it would be spherical , if it was a bit more massive than it actually is. So, Bob’s your uncle, it’s a dwarf planet too.

Ridiculous.

laurele
Member
February 20, 2015 12:16 PM

The issue isn’t whether an object is exactly spherical; it’s whether it is massive enough to be shaped by its own gravity rather than by its chemical bonds. Haumea is shaped by its gravity and is therefore a small planet.

Steve Nerlich
Member
February 20, 2015 9:56 PM
Laurele, Thanks for your response. I agree with what you say, but don’t agree the IAU have adequately constrained their definition of hydrostatic equilibrium. This is a product of mass AND the composition of matter to be compressed/shaped – e.g. an icy body would be shaped more easily than a rocky body. Also the IAU offers no constraint around the extent to which a body must be shaped by its gravity to achieve dwarf planethood. Most reasonably sized asteroids and comets are shaped by gravity to some degree even though they remain potato-shaped. So, where should we draw the line? 50% shaped, 75%, 90%? I don’t think a dwarf planet need be exactly spherical, but I object to… Read more »
FarAwayLongAgo
Member
FarAwayLongAgo
February 20, 2015 7:55 AM

What is a moon? (What about Trojan asteroids?)
What is an asteroid? (With a tail? Or a moon? Or a ring?)
What is a star? (How to strictly define a brown dwarf ex-star object?)
Can an asteroid become a moon, or even a planet? If two brown dwarfs merge, do they then become a star?

This list can go on and on and on. The interesting thing with astronomy is that everything gets more unique the closer one looks at it. Categorization is neither interesting nor useful.

lordxor
Member
lordxor
February 20, 2015 12:05 PM

It’s not a planet. Get over it and move on. There is nothing gained scientifically in calling it a planet. The “make Pluto a planet again” crowd is acting out of emotion and not any interests in advancing science.

Another thing: it is also only American’s making all the noise about it. The international astronomical community is happy with things the way they are.

Get over yourselves. Move on.

laurele
Member
February 20, 2015 12:22 PM
Wrong on multiple counts. Both the claim that support for Pluto’s planet status is driven by sentiment and the claim that it is limited to only Americans are false. These are straw men arguments designed to discredit those who oppose the IAU decision. Those who view Pluto as a planet do so because it is clearly spherical and orbits the Sun. It is obviously very different from and much more complex than the thousands of tiny KBOs in the Kuiper Belt. Many who oppose the IAU definition do so because they prefer a geophysical planet definition that first and foremost takes into account an object’s intrinsic properties rather than its location. Furthermore, support for the planet status of… Read more »
Wayfarer
Member
Wayfarer
February 20, 2015 12:21 PM

The term minor planet is already in use (much earlier than the term dwarf planet). Maybe you should just use the term dwarf planet, something like what Laurel described above, though I understand your differences with her

justin13
Member
justin13
February 20, 2015 2:43 PM

Maybe we’re looking at this from the wrong angle. Maybe Pluto, Ceres and their kind being dwarf planets isn’t the problem- maybe it’s Jupiter, Earth and the rest of the big 8 just being planets is the problem. Call them major planets, classical planets, or choose some other qualifier. Then major planets can be planets, dwarf planets can be planets, and everyone can enjoy the coming years and decades of discoveries. They’re interesting worlds regardless of what we call them.

Steven
Member
Steven
February 20, 2015 4:17 PM
Except that the “Classical Planets” do not include Neptune and likely not even Uranus. These are latecomers. ONLY 6 planets were known in “Classical” Greek and Roman times (Mercury, Venus, Earth, Mars, Jupiter, Saturn) – Prehistoric time for Jupiter, well before 2000 B.C. for Mars, before 1836 B.C. for Saturn, before 1581 B.C for Venus and before 1000 B.C. for Mercury. These are the “Classical Planets” Uranus may have been observed as early as Hipparchos in 128 BC and he included it his star catalog as a STAR. It was only in 1781 that Herschel presented his discovery as a comet or planet to the Royal Society and where it was accepted as a planet. In 1789, a… Read more »
Wizardwayne
Member
Wizardwayne
February 20, 2015 3:23 PM

I like the addition of a differentiated interior structure. But your definition of a “planet” would include a brown dwarf. It can’t fuse hydrogen, but can fuse lithium. I’d make that can’t sustain any nuclear fusion processes.

Steven
Member
Steven
February 20, 2015 3:26 PM
Lets address the double planet definition. The Barycenter theory is questionable. At some point Earth will be a double planet with the Moon as the moon continues to move away from the Earth. But let’s ignore that for now. I prefer the case made by Isaac Asimov in book “The Double Planet”. (http://en.wikipedia.org/wiki/Double_planet#Tug-of-war_definition). In that definition, a Planet always “falls” towards the sun. If two or more bodies orbit each other such that both always “fall” toward the sun then those bodies are a Double Planet, Triple Planet …. When considering the definition of a planet, one MUST consider orbital resonances and the effect that they have on “clearing the orbit”. For instance, the overwhelming gravitational effect of… Read more »
Wizardwayne
Member
Wizardwayne
February 20, 2015 3:39 PM

I COMPLETELY agree with your last statement. The definition must be based on measurable physical properties and defined by any arbitrary cutoff. I also agree with your argument including barycenter falling inside of the primary of two co-orbiting bodies.

Steven
Member
Steven
February 20, 2015 3:46 PM

… and if we apply the BARYCENTER rule, then the SUN is not the CENTER OF THE SOLAR SYSTEM. The barycenter of SUN-JUPITER is outside the surface of the sun so we would need to classify the Solar System as a “Double Star” referring to Jupiter as a FAILED STAR?

If we use the “falls” towards the SUN rule, then Jupiter is JUST ANOTHER PLANET!

So if we use the BARYCENTER RULE … what do we call Sun-Jupiter????

Kevin Heider
Member
Kevin Heider
February 21, 2015 12:19 PM

Trojan asteroids are trapped (DOMINATED) by the Sun and planet controlling them.

wpDiscuz
Become a Patreon and be a member of our club.