Why Pluto Still Matters (Synopsis)

If the disk of gas/dust that formed the planets was optically dense -even in the sense of a beam of light nearly parallel to its plane, wouldn't most of it have been mostly shielded from the suns heat/light? Perhaps the frost line was much further in?

The images are *very* interesting & informative, but this article seems a pointless and immature wish by an adult (who should be *glad* he's grown up and earning a living instead of living under Mommy & Daddy's thumb) for a childhood fantasy.

I was talking last night with my wife about one of my favorite childhood memories. I met Clyde Tombaugh, discoverer of Pluto, when he gave a lecture presentation at the Adler Planetarium in Chicago in the 1970's when I was in sixth grade. Mr. Tombaugh was an old man by this time. His lecture was sparsely attended. He stood small and stooped in a large auditorium talking quietly about his amazing experience. He was a bit Pluto-like himself as he stood on the stage.

After his lecture, I made my way to the front of the auditorium to ask for his autograph, which I still have. He was surprised! And he happily provided it. I was the only one in my school class and among my friends who loved astronomy. The moment was a personal achievement and one I have rarely described to anyone because not many people I know would appreciate it. That's sad.

I am very fond of Pluto! I wish Pluto would regain planetary status. Why? Sheer sentimentality, which is a phenomenon of the universe maybe unique to Earth.

My meeting with Mr. Tombaugh doesn't mean much to anyone who isn't me. However, like so many, many human moments, it occurred against the backdrop of the universe.

I guess I wish more people anthropomorphized Pluto. I would love to hear someone argue, "But Pluto wants to be a planet," as silly as that would be. That would be someone I'd show my Clyde Tombaugh autograph to; and that would be someone connected, albeit it in an unscientific although enthusiastic way, to some aspect of the universe's wonders.

Thank you for writing this article, Ethan!

Go, Pluto: we're pulling for you!

Eric,

I was a bit surprised when I saw the asteroid animation. It shows them following a somewhat triangular-shaped orbit with contrived vertices at Lagrangian points L3, L4 and L5. Is this true? If so, do the Trojans or the Lagrangian points themselves affect the asteroid orbits between Jupiter and Mars, or is it just the Trojans? Are there not also objects (like those shown as green on the animation) orbiting at L3, or do they only exist at L4 and L5?

Lastly, if this is true, would these orbital "vertices" also be called apsis points, as they normally are termed in elliptical orbits?

This is unusual, as I have never seen this illustrated or described before.

Sorry Ethan!. I know you are not namedEric! My mistake. I hit Submit Comment too soon.

But Pluto IS still a planet. You are still presenting only one view of an ongoing debate as reality when this is not the case. There is an alternative understanding of planet, the geophysical definition, which recognizes that Pluto is NOT like hundreds of objects in the Kuiper Belt. It is different because it is in hydrostatic equilibrium, rounded by its own gravity, a complex world with core, mantle, and crust just like Earth. The same is true of Ceres. According to the scientifically sound geophysical planet definition, used by the principal investigator of New Horizons, the only size that matters for an object is the one making it large enough to be shaped by its gravity, that is, to be in hydrostatic equilibrium. There are other KBOs such as Haumea, Makemake, and Eris that meet this definition, and it is important to distinguish them from the thousands of tiny objects to which you refer, which are simply iceballs shaped by their chemical bonds. The same is true for objects in the asteroid belt other than Ceres, Vesta, and Pallas. The latter two are so close to being in hydrostatic equilibrium that they deserve their own category, an intermediate one between asteroid and dwarf planet, possibly "protoplanet."

In short, the geophysical planet definition defines objects by their intrinsic properties, not by their location or by the properties of other objects.

Furthermore, your statement that Pluto has been surpassed in size regarding distance from the Sun is not true. Neither is your graphic, which erroneously depicts Eris is as larger than Pluto. Both ignore the fact that in November 2010, a study led by Dr. Bruno Sicardy determined Eris is marginally smaller, not larger, than Pluto, after Eris occulted a star.

We need a definition that recognizes that "regular planets" exist in a continuum that runs from gas giants more massive than Jupiter to small dwarfs the size of Ceres. This is not an emotional position.

To paraphrase your statement, the fact that there are other planets out there that are bigger, smarter, faster, stronger, or better than Pluto, in any regard, in absolutely no way diminishes not just how special Pluto is, but also its status as a regular planet.

@MandoZink, I've often wondered about the true meaning of a button labelled "Submit Comment". Its incorrect capitalisation alone is enough to give one pause for thought.

Perhaps it should be labelled "Press, then forever regret!" :-)

My dictionary gives this apt description of the word submit:
GIVE IN, yield, give way, back down, cave in, bow, capitulate, relent, defer, agree, consent, accede, conform, acquiesce, comply, accept; surrender, lay down one's arms, raise/show/wave the white flag, knuckle under, humble oneself, bend the knee, kowtow, fall; informal throw in the towel/sponge.
ANTONYM: defy.

Sentimentality is a part of the human psyche. I am heading for the 67 year mark this coming spring (for the northern hemispherians). I grew up with the 9 planets until recently, so Pluto still has a special place for me.
More the intrigue in the near future is the fact Pluto is about to be visited by us remotely, which will give us even more revelations about our existence; all good science. If we don't have dreamers, we have very little to think about. We have come to learn Pluto is not a planet per se, but it remains a part of our solar system
Thanks, Ethan, an excellent insight.

After it was reclassified, my sentimentality about Pluto quickly gave way to a certain scientific satisfaction. To me, it meant we've realized enough about solar system objects to more accurately categorize them.

Pluto IS unique in that it is the largest of it's kind, but it occupies a different niche than the inner planets. And there are other frozen bodies just like it, orbiting in it's realm, also unlike the inner planets. It's a more precise re-classification. Pluto is not a victim here. This is about astronomy getting better.

Pluto is a wimp. Just a moon-like planet wannabe. For years it hid out with its Kupier Belt orbital delinquents just making a bunch of gravitational noise hoping to get noticed. That happened all right. While it was trying to spoof a planet, hosting its own satellites and such, it was acting all cocky, going off the ecliptic and transiting its neighbor's orbit with an excessive ellipse just for spite. It took a good man like Neil DeGrasse Tyson to take action and put that hoar-frosted hooligan dwarf in its place.

Now I've got one word for you - Jupiter. There's a real planet! Big, lots of color, and it can take on a comet with no complaint. A little gassy maybe, but it makes up for it in sheer size. And it gots moons it can truly be proud of - active moons, not teeny-tiny frozen ones.

Pluto is a little moron. Sheesh! Because of this Plutogate mess, astronomers now might be unjustly suspicious of several other planets. And for what? You Pluto lovers can be real proud of yourselves. I hope you're happy.

Ron, #2, what evidence is there (evidence is a word meaning "that which is seen") for your assertion?

Or is this all just projection and sour grapes?

I am very fond of Pluto! I wish Pluto would regain planetary status. Why? Sheer sentimentality, which is a phenomenon of the universe maybe unique to Earth.

Point #1: That is no reason to make it a planet.

Point #2: Your claim of uniqueness is based on an argument from personal ignorance.

*Pluto is still there*. The man who discovered it *still is its discoverer*.

Why should it make it necessary to make it a planet? Ceres was a planet once. It was discovered and named a planet, then they discovered many other similar bodies in the same sort of orbit and we classed Ceres as an *asteroid*. NOBODY whined and pouted about how unfair it was.

Only 'Merkins with their 'Merkin Exceptionalism seem to have the overwhelming need for affirmation of their unique specialness to make a huge song and dance about their role in the world.

But Pluto IS still a planet.

No it isn't.

There is an alternative understanding of planet, the geophysical definition,

Of which, the only thing people bringing it up can say about it is the name. The definition entirely escapes them when pointing out that this claim:

which recognizes that Pluto is NOT like hundreds of objects in the Kuiper Belt.

DOES NOT APPLY to the definition of the "geophysical definition" since it inevitably includes AT LEAST a dozen other bodies and almost certainly around 200 currently known objects in the solar system.

Yet despite this inability, and despite the geophysical definition *BY PEOPLE WHO KNOW WHAT THE HELL IT IS* being considered *then rejected* as sufficient to create a definition of a planet, *it still* gets parroted by people who know nothing more about the word other than it's supposed to make pluto a planet.

We have not come to learn that "Pluto is not a planet." We have, since Pluto's 1930 discovery, had an ongoing debate among astronomers and planetary scientists as to whether or not it is a planet. We've learned it's part of a binary system, that it has five moons and atmosphere, but we still know little about it. The question of whether or not it is a planet is a not a matter of facts but of how those facts are interpreted. The Pluto controversy is far from the only ongoing debate in astronomy.

It is completely inaccurate to put Pluto in the same category as tiny, shapeless objects shaped only by their chemical bonds. That blurs a very important distinction, the question of whether an object has sufficient gravity to determine its shape. Objects that do, like Pluto, are far more akin to the larger planets than they are to tiny asteroids and comets.

It is also inaccurate to refer to Pluto as an "icy body," as its composition is estimated to be 70 percent rock. This distinguishes it from comets and most tiny KBOs, which are mostly ice.

Ceres is a planet too, according to the geophysical planet definition. 19th century astronomers' telescopes were not powerful enough to resolve Ceres into a disk, so they did not know it is round and therefore in hydrostatic equilibrium. Their demotion was therefore in error. Today, we know Ceres is spherical and a complex body, unlike the asteroids. Like Pluto, it may even have a subsurface ocean.

Wow, how do you know that nobody opposed Ceres demotion 150 years ago, since you obviously weren't there? Even if this was the case, that was a different time. Information traveled very slowly. Many members of the public may not have even known of Ceres' discovery. Certainly, no one knew of its complexity. Today, the transmission of information is instantaneous, and people don't have to rely on "experts"--they can do the research into these issues themselves, thanks to the Internet. Would you rather go back to a time when knowledge was limited only to a precious few "elites?"

So what if the geophysical planet definition include up to 200 other bodies? There is absolutely no scientific merit to the argument that we cannot have "too many planets." This is the paradigm shift that makes people uncomfortable--going from a small, countable number of planets to a large number. We already know there are billions of stars in the galaxy and billions of galaxies. The discovery of exoplanets has shown there are also billions of planets. Numbers in astronomy are huge, and planets are no exception.

Significantly, it was not "people who know what the hell it is" who rejected the geophysical planet definition. The 424 people who did that were mostly not planetary scientists but other types of astronomers. They never even bothered to consult planetary scientists.

I provided an explanation of the geophysical planet definition, so your claim that those of us who use it do not know anything about the term is false and nothing other than a personal attack.

The gas giants also occupy a different niche than the inner planets. That does not make them not planets. It just makes them a different class of planets. Dwarf planets constitute yet an additional subclass of planets. There are three classes of planets, not two.

Pluto and Ceres are complex worlds with geology, weather, and differentiation into core, mantle, and crust. They have the same features the larger planets have; the only difference is they are smaller. As for elliptical orbits, we have discovered giant exoplanets orbiting other stars with orbits far more eccentric than Pluto's. If an eccentric orbit precludes an object from being a planet, then what do you call these huge objects, some of which are larger and more massive than Jupiter?

As Dr. Stern said, " I can’t think of a single distinguishing characteristic that would set apart Pluto and other things that you’d call a planet, other than its size. So I like to say, a Chihuahua is still a dog."

@ ^ Laurel Kornfeld : Excellent comment and seconded by me.

I think the IAU got this debate and their definition of planet horribly wrong and will hopefully realise and change that sooner rather than later.

I think Pluto - and the other large ice dwarfs - count as planets and will note that a dwarf star is still a star so why should it be different for dwarf planets? It clearly should not not be from a consistent semantic and logical point of view.

Also if you put Earth or even larger worlds out where Pluto is they wouldn't be able to clear their longer orbits either showing just how silly and inconsistent the current - I think deservedly despised and temporary - IAU definition is.

Pluto is indeed special - and it is also actually a planet.

Laurel,

I fail to get why you are so upset about the IAU definition of planet. You correctly point out that Pluto is significantly different from those bodies not massive enough to become gravitationally rounded. It is also true that Pluto is different, as far as we know, from the gas giants and the inner planets in terms of its history and structure. Why then should Pluto be classified with EITHER of those groups? Why should it not receive its own classification (along with other similar Kuiper Belt objects). It seems to me that this is precisely what was accomplished with the designation of Pluto and similar objects as dwarf planets.

It is completely inaccurate to put Pluto in the same category as tiny, shapeless objects shaped only by their chemical bonds.

That is why the definition from the IAU doesn't. If you;re going to complain about the IAU definition, please limit yourself to those problems that ACTUALLY PERTAIN to that definition, rather than ones you made up yourself to rail against.

That blurs a very important distinction, the question of whether an object has sufficient gravity to determine its shape.

Gravity is only a small part of the definition. Structural strength too determines the shape.

THIS is why the "geophysical definition" so beloved by the whiner brigade is not acceptable to astronomers and astrophysicists.

It is also inaccurate to refer to Pluto as an “icy body,” as its composition is estimated to be 70 percent rock

It is also inaccurate (HIGHLY inaccurate) to claim Pluto consists of 70% rock, since that depends intently on the physical size of the object, which depends on composition and surface factors affecting albedo.

Pluto is between 30% and 70% rock.

Moreover, what is your complaint here? An icy body doesn't mean "only ice". Before complaining (this DOES seem to be a problem with your complaining), please find out what it is you are complaining ABOUT.

There is absolutely no scientific merit to the argument that we cannot have “too many planets.”

Yes there is.

Significantly, it was not “people who know what the hell it is” who rejected the geophysical planet definition. The 424 people who did that were mostly not planetary scientists but other types of astronomers

Wrong for a start.

Significantly only a handful of those people who wanted the geophysical definition taken on actually bothered to vote.

I provided an explanation of the geophysical planet definition

Indeed, you gave one. Everyone can, but they often choose a different one from anyone else's, and frequently change it. Moreover, your definition was insufficient to the task of defining a planet, with many problems in applying it.

As for elliptical orbits, we have discovered giant exoplanets orbiting other stars with orbits far more eccentric than Pluto’s.

Since the IAU definition doesn't exclude Pluto on the basis of its orbit being elliptical, again, your whine is irrelevant to the purported aim of your complaint.

PLEASE STICK TO REALITY. Thanks in advance.

Pluto and Ceres are complex worlds with geology, weather,

Pluto doesn't. Ceres has nothing to speak of in this department. Please don't enter a claim without having done any research.

Re other idiot:

I think the IAU got this debate and their definition of planet horribly wrong

You're entitled to your opinion, but nobody has to give a flying fig for it, IAU being one group.

Holding an opinion is like holding on to your own groin. Feels good for you, but nobody else wants to do it with you.