Why Pluto is No Longer a Planet
Written by Fraser Cain
This has got to be be one of the most heartbreaking questions I get asked, "Why Isn't Pluto a Planet". And I get it a lot. I was expecting that a few years after the International Astronomical Union's controversial decision, the debate would have settled down and people would finally accept it. But no, it's still a sore point for many people - Pluto is not a planet (let that sink in). In this article, I'll explain the events that led up to the decision, the current state of planetary definition, and any hope Pluto has for the future. Let's find out why Pluto is no longer considered a planet.
Pluto was first discovered in 1930 by Clyde W. Tombaugh at the Lowell Observatory in Flagstaff Arizona. Astronomers had long predicted that there would be a ninth planet in the Solar System, which they called Planet X. Only 22 at the time, Tombaugh was given the laborious task of comparing photographic plates. These were two images of a region of the sky, taken two weeks apart. Any moving object, like an asteroid, comet or planet, would appear to jump from one photograph to the next.
After a year of observations, Tombaugh finally discovered an object in the right orbit, and declared that he had discovered Planet X. Because they had discovered it, the Lowell team were allowed to name it. They settled on Pluto, a name suggested by an 11-year old school girl in Oxford, England (no, it wasn't named after the Disney character, but the Roman god of the underworld).
The Solar System now had 9 planets.
Astronomers weren't sure about Pluto's mass until the discovery of its largest Moon, Charon, in 1978. And by knowing its mass (0.0021 Earths), they could more accurately gauge its size. The most accurate measurement currently gives the size of Pluto at 2,400 km (1,500 miles) across. Although this is small, Mercury is only 4,880 km (3,032 miles) across. Pluto is tiny, but it was considered larger than anything else past the orbit of Neptune.
Over the last few decades, powerful new ground and space-based observatories have completely changed previous understanding of the outer Solar System. Instead of being the only planet in its region, like the rest of the Solar System, Pluto and its moons are now known to be just a large example of a collection of objects called the Kuiper Belt. This region extends from the orbit of Neptune out to 55 astronomical units (55 times the distance of the Earth to the Sun).
Astronomers estimate that there are at least 70,000 icy objects, with the same composition as Pluto, that measure 100 km across or more in the Kuiper Belt. And according to the new rules, Pluto is not a planet. It's just another Kuiper Belt object.
Here's the problem. Astronomers had been turning up larger and larger objects in the Kuiper Belt. 2005 FY9, discovered by Caltech astronomer Mike Brown and his team is only a little smaller than Pluto. And there are several other Kuiper Belt objects in that same classification.
Astronomers realized that it was only a matter of time before an object larger than Pluto was discovered in the Kuiper Belt.
And in 2005, Mike Brown and his team dropped the bombshell. They had discovered an object, further out than the orbit of Pluto that was probably the same size, or even larger. Officially named 2003 UB313, the object was later designated as Eris. Since its discovery, astronomers have determined that Pluto's size is approximately 2,600 km (1,600 miles) across. It also has approximately 25% more mass than Pluto.
With Eris being larger, made of the same ice/rock mixture, and more massive than Pluto, the concept that we have nine planets in the Solar System began to fall apart. What is Eris, planet or Kuiper Belt Object; what is Pluto, for that matter? Astronomers decided they would make a final decision about the definition of a planet at the XXVIth General Assembly of the International Astronomical Union, which was held from August 14 to August 25, 2006 in Prague, Czech Republic.
Astronomers from the association were given the opportunity to vote on the definition of planets. One version of the definition would have actually boosted the number of planets to 12; Pluto was still a planet, and so were Eris and even Ceres, which had been thought of as the largest asteroid. A different proposal kept the total at 9, defining the planets as just the familiar ones we know without any scientific rationale, and a third would drop the number of planets down to 8, and Pluto would be out of the planet club. But, then… what is Pluto?
In the end, astronomers voted for the controversial decision of demoting Pluto (and Eris) down to the newly created classification of "dwarf planet".
Is Pluto a planet? Does it qualify? For an object to be a planet, it needs to meet these three requirements defined by the IAU:
- It needs to be in orbit around the Sun - Yes, so maybe Pluto is a planet.
- It needs to have enough gravity to pull itself into a spherical shape - Pluto…check
- It needs to have "cleared the neighborhood" of its orbit - Uh oh. Here's the rule breaker. According to this, Pluto is not a planet.
What does "cleared its neighborhood" mean? As planets form, they become the dominant gravitational body in their orbit in the Solar System. As they interact with other, smaller objects, they either consume them, or sling them away with their gravity. Pluto is only 0.07 times the mass of the other objects in its orbit. The Earth, in comparison, has 1.7 million times the mass of the other objects in its orbit.
Any object that doesn't meet this 3rd criteria is considered a dwarf planet. And so, Pluto is a dwarf planet. There are still many objects with similar size and mass to Pluto jostling around in its orbit. And until Pluto crashes into many of them and gains mass, it will remain a dwarf planet. Eris suffers from the same problem.
It's not impossible to imagine a future, though, where astronomers discover a large enough object in the distant Solar System that could qualify for planethood status. Then our Solar System would have 9 planets again.
Even though Pluto is a dwarf planet, and no longer officially a planet, it'll still be a fascinating target for study. And that's why NASA has sent their New Horizons spacecraft off to visit it. New Horizons will reach Pluto in July 2015, and capture the first close-up images of the (dwarf) planet's surface.
Space enthusiasts will marvel at the beauty and remoteness of Pluto, and the painful deplaneting memories will fade. We'll just be able to appreciate it as Pluto, and not worry how to categorize it. At least now you know why Pluto was demoted.
If you'd like more information on Pluto, we did two podcasts on this topic at Astronomy Cast. The first discusses the IAU's decision, and the second is about Pluto and the Icy Outer Solar System. Check them out.
Here is much more Pluto info, including pictures of Pluto.
April 10th, 2008 at 2:04 pm
Sad? Really? I find it a great opportunity to demonstrate with a timely and easy example that scientific knowledge is provisional and changes as our understanding changes. It's one of the best ways to steer learning minds clear of absolutism and dogma, which is often confused with actual science.
I was always excited by the idea of Pluto as a planet had gone un-noticed for a long time, but while the sentimentality of its status is lost, the change creates a great opportunity for education and understanding of science as a changing body of knowledge, not static.
April 10th, 2008 at 2:10 pm
The most accurate measurement currently pegs Pluto at 1,195 km (743 miles) across. Although this is small, Mercury is only 2,440 km (1,516 miles) across.
I think those are radii, not diameters. Same for Eris.
April 10th, 2008 at 2:16 pm
Oops, you're right. Thanks!
April 10th, 2008 at 2:17 pm
At least Bill Arnett had a sense of humor about it when his domain name proved to be incorrect (look at the title): http://nineplanets.org/
Plus he also had the foresight to add eightplanets.org to his stable to domain names.
April 10th, 2008 at 2:30 pm
For one side, you can be happy as you are not Pluto, who has the right to demoting it?
There are animal protection groups, Pluto would have to have its own. (That lazy astronomers…).
But yes, it could be more acurate to say that pluto and its neighbour are a planet in formation and the New Horizonts is of prime importance to study this medium.
April 10th, 2008 at 2:31 pm
Actually, I still think this definition makes very little sense. Not because of Pluto: Pluto's status is, or should be, pretty much irrelevant in the debate, but because of other things:
- The "clearing the neighborhood" thing is totally arbitrary in what constitutes a "clean neighborhood", or even a "neighborhood".
- The fact that in our solar system planetary neighborhoods are clean, whatever that might mean, does not imply that the same is true in other planetary systems: theoretical studies have shown that 1:1 resonances between planets as large as gas giants are completely possible, and, given the vastness of space, what's possible will almost certainly be found, somewhere. In my opinion, any definition of planet that isn't universal or that excludes gas giants is… er… dumb.
- As planetary sistems evolve, neighborhoods become increasingly "cleaner" with time, in average. In young systems, you'll have planets as large as the Earth, or even larger, with "dirty" neighborhoods, wereas in old systems, smaller and smaller bodies get their orbits cleaned up. Ceres might well become a planet some day, without changing the least bit.
- Furthermore, due to the shorter distances and faster speeds involved, neighborhoods clean up faster in the inner system than in the outer system. I find it hard to accept a definition that is capable of calling "planet" to a body that is at the same time smaller and less massive than another one just because it's closer to its star.
- And so on.
So, personally I think the gravitationally caused roundness criterion would have been much, much sounder, even if it isn't perfect. And after deciding that planets are thnigs forced to roundness by their own gravity, they should be subdivided in categories. The only real change would be that dwarf planets would be planets too, albeit dwarf. It even makes more linguistic sense than saying that dwarf planets are not planets.
April 10th, 2008 at 2:47 pm
I have to agree with Gorge on this one.
As far as I know as well, the definitions for the planet and dwarf planets are applicable to our solar system only.
I mean if we find a young system with a body larger than earth that is still in the middle of a plantery disc surrounded with dust, rocks and what other junk you may find, it isn't classified as a planet until a much later date.
Seems to sound like a planet will go through a cycle much like a star being from main sequence to red giant, it will just take much less time for inner, terrestrial planets to gain the status, despite having massive jovian planets multiple hundreds of times larger still being classified a dwarf planet because they take much longer to orbit and may not have "cleaned" it up.
Should have just stuck with 9 planets and classify the KBO's as what they are, KBO's.
April 10th, 2008 at 3:23 pm
I think that, with a nod to a colorful history (Percival Lowell), we should just keep Pluto as a planet.
April 10th, 2008 at 3:30 pm
I thought that Pluto is not even considered its own planet, even in the dwarf category.
I am under the impression that Pluto and its counterpart, Chiron, rotate around a shared center of gravity, thus making it a binary system. Why am I thinking that Pluto-Chiron is classified by the IAU as a "Double Dwarf Planet?"
April 10th, 2008 at 4:25 pm
¿Por qué Plutón no es un planeta? Esta tiene que ser una de las preguntas más desgarradoras que me han hecho. Y me la preguntan seguido. Esperaba que algunos años después de que la Unión Astronómica Internacional (IAU) tomara esta decisión polémica, el debate decayera y la gente finalmente lo aceptara. Pero no, todavía es un asunto delicado para mucha gente. [...] Fraser Cain para Universe Today
April 10th, 2008 at 5:51 pm
I've never understood why this gets people so worked up.
Wasn't the thinking behind the "clears its orbit" criteria basically that there probably are a large number of probably spherical objects orbiting the sun, and it would become confusing if one day there were, say, 35 planets.
In that case we'd probably have to create a categorization of "major planets", which would exclude pluto anyway.
April 10th, 2008 at 7:38 pm
Pluto is made up of the same materials as Uranus, Neptune, Titian, and Triton. This is only one factor that determines the type of planet it is. Mass is a second factor. Clearly, Pluto lacks the ice giants mass, but has enough to be round. Location is another. Pluto was exiled early the solar system's history to the Kuiper Belt.
The Neptune Effect made the current configuration of the solar system. It moved the ice giants, Uranus and Neptune to the outer solar system with Pluto and probably Eris.
Dwarf stars are still considered stars. Dwarf galaxies are also considered galaxies. Pluto, Ceres, and Eris should be considered smaller planets. We are going to find a lot bigger objects out there. S. Alan Stern predicted Earth sized Kuiper Belt Objects. Let's keep Astronomy honest. These are just a new class of planet. Stern believes they are the largest category of planets.
April 10th, 2008 at 8:35 pm
I saw a good t-shirt the other day: it had a picture of Pluto with a sad looking face on it, and said: "Don't worry Pluto - I'm not a planet either…"
But seriously…
Look, the term planet is just an arbitrary human classification anyway. In reality, nature is more continuous than discreet, and has more variety in its processes than we could ever hope to have a label for.
It reminds me of an interview with Richard Feynmann, where he was talking about how his father had taught him to look beyond superficial labels - it went something like this: His dad took him for a walk and showed him a bird. He said "people will tell you that that bird is a (insert name of bird here), but they don't really know what it is or anything else about it. To know that, you have to actually look at what it is and what it does. How it behaves and acts. They are just giving it an arbitrary label."
Do it is with the Pluto debate to a certain extent. Pluto is still there - it is an inanimate object. It doesn't care what you call it, because it is what it is. We should be much more concerned about studying it, not getting worked up over precise definitions of it, no matter how useful such things may be to our very human need to classify everything into neat little compartments.
Yes, it is a controversial descision, and yes, the IAU definition certainly lacks, because how do you define 'cleared out its orbital neighborhood' in any quantitative way that is not completely arbitrary? But the fact is, Pluto is fundamentally different from those objects that we call 'planets' based on the available evidence, so it makes sense to classify it officially as such.
April 10th, 2008 at 11:04 pm
Personally, I could care less if its a "dwarf planet" or other wise. I do think that todays elementary school books should include ALL of these known massive solar bodies. When I was in school Pluto was a planet. But they also taught us in school that South America and Africa werent ever connected!! This is obviously ludicris now. We now know that at one time all the continents were one giant continent.
Anyway, my point being that schools should teach about all the massive solar objects beyond Neptune.
Infact, Im a little dissapointed in the fact that I wasnt taught about Varuna or Orcus or any of the objects beyond Neptune except Pluto
Even in a book I own (thats new btw) about astonomy, it doesnt even mention these other objects. Dwarf Planets, Planets, giant Astroids, I think they should all be in the same section.
April 10th, 2008 at 11:39 pm
And isn't there also one called Ixion…?
April 11th, 2008 at 1:31 am
Hi There,
Cleared its own orbit? Well even Jupiter has Trojans, small asteroids 60 degees ahead and behind the planet but they are there because of the gravity of Jupiter.
Also Pluto comes inside the orbit of Neptune for some 25 years and its inclination to the plane of the ecliptic is high. Two features that are not like conventional planets.
I like the idea of eight planets - for young kids it is easy to grasp, then when older they can be taught dwarf planets, then again asteroids and all the families of bits of rock that orbit our Sun.
April 11th, 2008 at 2:49 am
Let's not forget that the asteroid Ceres in the main asteriod belt between Mars and Jupiter is almost 600 miles in diameter and is spherical like a planet. It, like Pluto, meets only two of the three IAU criteria for defining a body as a planet. If Pluto is a planet than Ceres and all the outer dwarf planets must be full-fledged planets as well. Considering that there may be HUNDREDS of large spherical bodies not yet discoverd in the outer solar system, we better be happy with just Eight planets…I, for one, do not want to have to remember the names of the dozens and dozens of planets in our solar system the next time I play trivial pursuit!
April 11th, 2008 at 3:10 am
What a mess!
A lot of people seem concerned with the "how many are there?, 8?, 9?, 12?" issue that has no scientific meaning.
Although I understand the criteria, the motivation behind it seems taylored to the "How many" issue, in result the current definition of planet is not very good beacause, with it, for you to classify an object, you must know where it is, how does it moves and what's arround it.
This is not very practical; Check these examples:
Ex 1: Think of all those exoplanets that are being discovered… According to the current definition some of them might turn up to be "exo-dwarf-planets"… Ridiculous!
Ex 2: Imagine a planet arround a sun (A planet according to the current definition) imagine, then, that some astronomical phenomenon yanks this planet out of it's orbit mantaining all it´s characteristics… And, since it no longer is orbiting a sun, then, no longer is a planet… Ridiculous!
I would favor separate classifications for what an object is and for where it is (and how does it move).
I would say that any object that is spherical due to it's own gravity and it's not ignited (like a sun) nor extremely dense should be called a planet.
With this defnition in mind we could, then, say that:
-Some planets are moons (beacause they orbit other planets - our Moon would be a planet);
-Some planets are free (because they're not orbiting anything and are just wandering in space) - I'm sure these objects exist.
-Some planets dominate their orbit…
-Etc…
You would just need to see it to state: "This is a planet!"
Nuno
April 11th, 2008 at 3:17 am
…And let's face it…
A lot of them fires up our imagination (at least mine).
Wouldn't it be more poetic to go on a turistic travel arround, say, Planet Ceres than the same turistic travel arround asteroid Ceres?
Nuno
April 11th, 2008 at 4:52 am
I have a lot of detailed opinion I'll spare you all, and offer this one observation.
Few planets have inspired an interest in astronomy more than Pluto. Declassifying Pluto is yet another uninspired decision that harms the public interest in a science that already has difficulty justifying public expense. There is a better classification than the one adopted, but even if they went with the new definition, there should have been a forth qualification:
"If previously categorized as a planet". Then we keep Pluto as a planet, and are not inundated with scores of new planets.
April 11th, 2008 at 5:32 am
Pluto is still the same, It doesn't matter what people call it.
Whatever the accepted definition of a planet is, stuff in some other solar system will still be stuff in some other solar system. People like to put things into categories, and sometimes you can look past this.
April 11th, 2008 at 6:01 am
John Molina: "I am under the impression that Pluto and its counterpart, Chiron, rotate around a shared center of gravity, thus making it a binary system"
In fact John, all systems rotate around a shared centre of mass, including the Earth and Moon, which is more properly referred to as the Earth-Moon system. In this case, the centre of mass is deep within the Earth, making it *appear* as though the moon "goes around the Earth".
Even Jupiter and its moons rotate around each other, but of course the centre of mass in this system is right in the middle of Jupiter itself.
Personally I would not consider Jupiter and its moons to be a "binary" system. I would guess that a system could be considered "binary" if the centre of gravity is somewhere close to the middle of an imaginary line drawn between the 2 objects. Put another way, the mass ratio of the objects would be close to 1.
April 11th, 2008 at 6:22 am
I agree with the above responders, by my own objections - questions:
which other body is in Pluto's orbit?
Charon is a Pluto`s satellite or Pluto-Charon is a "binary" planet (now an ex planet), as MANY binary stars, orbiting each other by them gravitational center.
A point with i will agree to this demotion, is that Pluto`s orbit is crossing the Neptune`s respective, as Ceres is crossing Earth`s, and it is an asteroid.
Finally as a Greek citizen i have emotional reasons, due to ancient Greeks history, when Pluto was the underworld`s God, ALL THE OTHER PLANETS are named with ancient Greek Gods.
April 11th, 2008 at 8:02 am
Of course the objects remain the same regardless of how one classifies them. But if we want a classification that has some scientific value, we better make it as good as it can get.
And the fact is that the only real and universal way to split what's planet-like from what isn't (in the lower-mass part of the scale) is roundess caused by self-gravity. It certainly isn't perfect, surely we'll have a small group of transitional objects (EL61, probably Vesta), and there are also factors such as constitution to take into account, but these are much smaller problems than all those that arise from the orbital clearing thing.
As for the number… why is it even a factor? To tailor a definition in order to keep a given number of objects in a category has absolutely nothing to do with sicence. A definition of what a planet is has to be about what it IS, not about how many fitting candidates there are. So what if the Solar System has hundreds of planets? Kids can't memorize them all at school? What does that have to do with science?
In OUR solar system, there are eight known major planets, including 4 gas giants and 4 terrestrial planets (even though Mercury is fundamentally different from the other three). In what we know about OUR solar system there is a clear distinction between those and the dwarf planets, which are officially three but might be a lot more. But in OTHER solar systems there may well be no distinction at all, although we have so far only found big bodies, with the exception of those early pulsar planets. This is what kids at school should be taught. The parroting of the names may be cute, but it's really not teaching them much.
April 11th, 2008 at 8:24 am
The most absurd feature of this new nomenclature is that it is linguistic nonsense.
So, a dwarf planet is not a planet, then?
That's as daft as saying that a brown cow is not a cow! This is such an obvious error that it beggars belief that a bunch of so-called intelligent people can come up with such a name; if you are going to have a different category of solar-system object, you need a separate word, like 'planetoid' or 'pluton'.
I rest my case.
April 11th, 2008 at 8:25 am
I still don't understand why so many people has problems with the notion of having a lot of planets in our solar system.
The problem of having a manegeable list for educational purposes is hardly a good argument.
We have a lot of Stars out there and neither in education or public opinion the interest on studying them is weakened beacause there are so many. On the contrary! (We learn the names of a handful, but there's no need to downsize catalogs).
If we absolutely need to downsize planet lists to "humanly interesting sizes", try the folowing:
- The number of planets that can be seen with naked eye…
- The number of planets that can be studied with a small telescope…
Also find disappointing why people view the changes in designation as demotions or promotions.
We shouldn't gain or loose interest on these objects in function to their classification.
I hope someday they change the current criteria, not beacause of Pluto, but because it goes arround the wrong premisses.
Nuno
April 11th, 2008 at 8:34 am
I couldn't agree more with Keith Atkin…
…e concordo plenamente com o Jorge…
April 11th, 2008 at 10:07 am
It all seems to be a lot of teeth gnashing about nothing to me. It’s like trying to decide when a hill becomes a mountain or a stream a river. We all intuitively seem to know when that happens. So draw a line in the sand and move on. State there are 8 planets, no more, no less. Anything else is simply a “named object” unless it happens to get close to the sun and grow a tail. Then it’s a comet. Done. After all – look at an Earth globe and you’ll only see six continents. The whole Europe/Asia thing is just political…
April 11th, 2008 at 12:51 pm
My 2 cents worth.
I was always troubled by the 9 planet notion in my text books and numerous definitions and categories that are always present in science - any science. It seemed to me that in any field of study we spend our first couple of years in college learning the terms, the definitions, the theories that are often presented as facts and of course the categories. This is important as a way to get us speaking in terms that we can communicate on a higher level, but I always called it BSology.
If a star is being sucked into a black hole, is it not a star because it hasn't swept up it's orbit? If a planetoid body has moons, has it really cleaned it's orbit? The moons of Mars are moving into a higher orbit; if they someday escape the gravitational pull of Mars, then is Mars no longer a planet? Is a binary system no longer a planet in these new definitions? The whole method of categorizing is offensive to my way of thinking.
In time we will discover newer solar systems where the planets have failed to sweep their orbits up and will that mean that they aren't planets? What if one is larger than our Earth and hasn't consolidated it's mass into a ball; is it not a planet? I could go on like this without serving further purpose. I believe that we need to change our basic way of looking at things and not get stuck in definitions that don't work. To me all of the objects in our solar system that are round are planets including our moon and other satellites that orbit Jupiter and Saturn. Without counting, there must be about 30 known planets on my list. Categorizing them doesn't change what they are or the fact that all of them are well worth our time to study and try to understand how they came to be and why they differ from one another.
Besides, who gave one group of scientists the right to vote on the subject?
April 11th, 2008 at 1:28 pm
Pluto has some interesting planet - like characteristics.
It has at least 3 moons. (As many as Mercury, Venus, Earth and Mars combined.)
It has an atmosphere. (That's more than Mercury.)
It orbits the Sun.
We need a good definition for Planet. It should work for extrasolar planets. It should work for the public. The dynamics concept does not work for the public. Worse, it's badly stated, so to the letter, it works for noone. That comes from it's being cobbled together at the last second. The committee proposed a definition. The IAU should have voted it in or not.
We went through this in 1850, and Ceres, which had been a planet, was demoted. The minor planets were invented. We compounded this by inventing Dwarf Planets. Now we get to argue if a Dwarf Planet is a Planet or not. But the minor planet center gave Pluto a number.
With the dynamic clause, there is only one planet. Jupiter is clearly the gravitational bully of the solar system, after the Sun. All other objects are in resonance with Jupiter. So, the Earth needs a minor planet number. I suggest zero.
April 11th, 2008 at 3:28 pm
The number of planets means nothing.
Clearing its neghborhood… Wah! Who cares?
I admit I was a little miffed when Pluto was demoted, only because it seemed like they were killing a long time friend.
Then I saw a show that Neil Degasse-Tyson explained how Pluto has an atmosphere the fades away as it aproaches the sun, which means Pluto is more like a permanent (sort of) long- long term comet. That made the Kuiper belt all that much more COOL and Pluto became a very unique and EVEN MORE cool friend again. When we finally get out there, we are going to find all kinds of great stuff, and THAT is all that matters to us space people. That means they'll have to come up with a new category of Cometessimals or permanent Comets and stuff. We all love Pluto, lets give him his proper attention and congrats on his great new status as being truly unique!! At least until 2015- anyway!
I wish we'd have known about the Kuiper Belt when I was in grade school!!!
Neil Degrasse-Tyson is the new Carl Sagan!!!
April 11th, 2008 at 3:44 pm
Oh yeah, I forgot.
The term "planet" was in dire need of a true definition. It had no real definition for 5 or 6 or 7 thousand years. (Give or take a few centuries)
The Sun was originally a planet and so was the moon. One was hot and the other was not. Sounds PRETTY stupid now doesn't it??
As science progresses, so must our thinking.
Before we realized germs caused diseases, we thought they were caused by demons…………..
Need we say more?
Knowledge is progress, can't have one with the other. Shall we move on?
BTW, the last article I read on Mars' moons stated that BOTH of them are destined to CRASH into the surface, not fade away. Mars would still be a planet anyway because of its mass and orbital plane/"neghborhood". They failed to put mass into the equation and I agree, That was a mistake.
Our Moon is fading away at 1.5 inches a year. We will still be a planet in 1 billion years, if for no other reason than because "they" SAY SO. LOL
April 11th, 2008 at 4:58 pm
Gudenboink, I know you're just kidding, beacause you probably know that the term "Planet" comes from a Greek word that means "rogue" or "wanderer"…
Obviously the term reflected the odd nature of some objects in the sky that didn't move along with the rest. Those objects just seemed to "wander arround".
So it made sense to call planet to every object in firmament with this "wandering" nature (that included the Sun and the Moon).
Only later, when we got to grasp the kind of things that were seeing and the origin of the term got forgotten, the designation excluded the Sun and The Moon…
Nuno
April 11th, 2008 at 7:00 pm
I humbly stand corrected. The moons of Mars are indeed losing orbital radius. Thank you Gudenboink.
I think the issue that causes Pluto to be dropped from the list is that it is made of volatile material and wouldn't stand a chance if it were closer to the sun. I still think that it deserves study and I don't like the idea of creating a lesser category that may cause the excitement of astronomy to be dropped from kids textbooks. These outer objects, Kuiper belt objects are the most interesting things being explored in the solar system today. Many people believe that the water on the Earth has it's origin in such objects that may have crashed into the Earth. I can't wait to discover and learn about more of them.
April 13th, 2008 at 9:11 am
I agree Ray,
Where else could all that water have come from? The fact that Pluto CAN'T exist close to the Sun means we are going to find all kinds of great new "stuff" when we finally get out there. I'll bet all the objects we find in the Kuiper Belt have multiple moons, a second huge asteroid belt and comet graveyard.
I wish the scientific/engineering community would get over this "anti-nuclear power propulsion" crap so these adventures didn't take so long. New Horizons made it past the moon in 8 hours and Jupiter in 3 months. I realize at that speed we only get 1 - 2 days of Pluto pictures and info, but we probably wouldn't be able to orbit that kind of a system anyway.
It's obvious to me that we won't really put a dent in exploration until we come up with faster more effective and efficient propulsion.
We've had proven technologies on the books since the 60's, and not only with nuclear propulsion. Safety is a huge factor, but we've had 40 years to make it safer.
I'd like to live long enough to find "life" out there. Selfish - I know - I guess I'm still bitter about killing the manned space program in 1972. I always will be because we wasted 25 years of huge leaps in space tech.
April 14th, 2008 at 2:53 am
I agree that Pluto is not a "really" planet.
What I don't understand is that why this type of classification is not apply in the case of moons. There are really big moons, and other small and less important objects. It'll be easy to split them in 2 categories.
April 16th, 2008 at 5:00 am
What I don't get is why is Uranus a planet ? If Uranus has not "It needs to have "cleared the neighborhood" of its orbit - Pluto… nope.
" ?
As I know Pluto intersects Uranus orbit .
April 16th, 2008 at 10:50 am
What is truly sad is the fact that the demotion of Pluto was done in a controversial political, not scientific, manner. The definition adopted was done so on the last day of the IAU's two-week conference by four percent of its members, most of whom are not planetary scientists. The terms of the resolution adopted were changed over and over right onto the last day. No electronic voting was allowed, so the 96 percent of IAU members not present in the room had no say whatsoever. Immediately, over 300 professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA's New Horizons mission to Pluto, signed a petition saying they will not use the new definition, which Stern described appropriately as "sloppy science that would never pass peer review."
As somebody else on this board stated, the IAU definition, which states that a "dwarf planet" is not a planet at all makes no linguistic sense. That is like saying a grizzly bear is not a bear. And the only reason it is considered "truth" is that the resolution that would have established both "classical planets" and "dwarf planets" under the broader umbrella of planets was voted down by the IAU 333-91. That's not exactly a ringing endorsement.
In astronomy, dwarf galaxies are still galaxies, and dwarf stars are still stars (our sun is a dwarf star!).
There is no reason why an object cannot be both a Kuiper Belt Object and a planet if that object has achieved hydrostatic equilibrium, meaning it has enough self-gravity to pull itself into a round shape. These objects have geological processes and compositions far similar to those of the planets than those of asteroids or comets. Pluto is not a comet; its orbit does not take it into the inner solar system, as the orbits of comets do.
As for the requirement that an object "clear its orbit" to be considered a planet, this determination is highly subjective. Applied literally, it would exclude all the planets in our solar system. It most certainly excludes Neptune, which does not clear its orbit of Pluto. There is no reason that "clearing its orbit" should be a criteria for planethood. This is an extremely arbitrary determination. The further away an object is from its parent star, the more likely it is to have other objects in its orbital path.
The smart way to deal with the discovery of these new round KBOs is to keep the term "planet" as a broad category and then establish multiple subcategories, such as terrestrial planets, gas giants, ice giants, and ice dwarfs. Moons of planets that have achieved hydrostatic equilibrium could be considered secondary planets since they revolve around other planets rather than around stars. If this leads to over 100 objects falling into the broad category of planets, so be it.
This debate will not settle down because a flawed definition adopted through a very flawed process is a poor substitute for true science.
As a result of this decision, people have been further alienated from astronomy, and few people even know about Eris and the other round KBOs, which should also be considered as falling under a subcategory of planets. My guess is that adding these objects instead of taking away Pluto would have excited the public and led to more people developing and pursuing an interest in astronomy.
In conclusion, I will advance the definition put forth by my astronomy instructor Al Witzgall, which makes the most sense and should be the one ultimately accepted by science. In his words, a planet is "a non-self-luminous spheroidal object orbiting a star." That's it. And under that definition, Pluto IS a planet.
April 17th, 2008 at 11:52 pm
Ever heard of guinea pigs or panda bears? ALL human languages are full of nonsenses. The thing is: quite probably, we will find a body a little bit smaller than Pluto (say, 80% of Pluto's radius), and another one (70 %), and another… Should we name them planets as well? Then we will end up calling every single bit of a rock that's VAGUELY spheroidal (never seen a perfect ball in our Galaxy) and orbiting Sun a planet. Does that make sense? Not to me. Every criterium can be called political: mass, diameter, orbit radius, shape of orbit (couldn't find english translation of polish mimośród, sorry!). And, finally, does calling Pluto (and ceres, Eris etc.) a planet is really THAT important?
April 18th, 2008 at 6:26 am
This is a really lovely description and article, and shows great insight in the scientific process.
One thing that I wonder about, though: what about sister planets of approximately the same mass sharing an orbit in a stable, low number configuration (very improbable, but technically possible)? Would that technically make them dwarf planets according to our current definition, independent of size?
April 18th, 2008 at 6:57 am
i dont like this website
April 18th, 2008 at 6:58 am
i dont like this website i does not give me info
April 18th, 2008 at 9:16 am
can anyone explain this to me….
i was looking out from an airplane's window, and from a distance, not very far, i saw 3 or 4 huge metallic round beams protruding from a group of clouds.
i was staring at those big posts for several minutes with my own naked eyes…. and it's been a year i've been wondering what those might be.
???
April 27th, 2008 at 12:13 am
Laurel Kornfeld, You are a Genius!
Your concept of making the planets more diverse and sub categorize them makes a ton of sense! Making more planets and expanding them is a positive way to get more interest generated especially with kids. Taking away is a negative that will dwindle excitement..
Who cares how many planets, dwarf planets or sub planets there are?
It's as if the 4 percent of the people that voted were worried about how much paper they will use up in documenting the changes!!!!
April 28th, 2008 at 10:03 am
i dont like it ????????
rubhish
April 28th, 2008 at 6:38 pm
I like the info my real name is Carly Shay .Thanxx for info of Pluto
Please type back Carly Shay
April 29th, 2008 at 9:45 pm
Sad PlutoT.T
May 1st, 2008 at 3:48 am
CUTE PLUTO
May 1st, 2008 at 7:41 am
okay lets see here.. yall say pluto isnt a planet anymore because he doesnt fit the defenition of what a planet is.. well how about this for you..say you have a brother or sister and he/she is mentally challenged.. would yall want them not considered a person?cause technically they dont fit the defention of a person.i have nothing against mentally challenged because my cousin is mentally challenged.. i just think its stupid that yall want to say that pluto isnt a planet anymore..
May 3rd, 2008 at 10:56 am
Hello Jessica,
It's not to say Pluto isn't a planet anymore, it's just due to new scientific data, the time has come to re-define and categorize what we've learned. Pluto is a different TYPE of Planet. We now have EXO-planets and Hot Jupiters, it was bound to happen eventually.
I was really P-O'd when they demoted Pluto cuz it felt like they had killed a friend. Then my ten year old nephew said something that surprised me. He said "It's the science that matters." He's right.
Change takes time to get used to, especially when you've grown up all your life believing something.
Instead of demoting Pluto, we promoted him / "it" to the top of his own category of planetary objects making room for new stuff when we get out there in a few years.
There are several objects in an Earth-orbit proximity that could classify as moons, technically. But they are more space rock than moon because they don't really effect Earth. Similar to how some of Jupiter and Saturns moons are WAY out in La La Land- they are just rocks.
Pluto is more comet than Planet and by the time we find more of them, we will all be used to talking about Pluto in it's new category.
I wish the space community would start using nuclear propulsion so these space probes didn't take as long to get to where they are going as they take to invent. By now - the probes should be traveling twice as fast as they did in the 1970's, and they could be. Nuclear isn't as unsafe as it was 30 years ago. The public has to realize that Nuclear does not equate to destruction anymore - it means Technology - Medicine - Energy - Science and the future.
May 3rd, 2008 at 9:07 pm
Gudenboink, you're right in saying Pluto is a different type of planet. But that does not mean it is not a planet at all! It most certainly is not a comet, as its orbit is far more like those of the planets than those of comets. Unlike comets, Pluto's orbit never takes it into the inner solar system. And Pluto likely has geological processes that comets and asteroids do not have. Why not add a new subcategory of planets to fit objects like Pluto, Eris and even Ceres? A huge problem with the current definition could be addressed by simply categorizing "dwarf planets" under the broader umbrella of planets. It is not good science to lump these objects in with the asteroids or comets, as they are fundamentally different from them. And we are likely to find more of these objects in the Kuiper Belt over the next few years, distinguished from most KBOs by their size and round shape.
May 6th, 2008 at 2:32 pm
As children talk about Pluto in their classrooms, we hope that teachers tell us correct information about space. Our teachers still are teaching that Pluto is a planet. What would you advise us to tell them?
May 9th, 2008 at 11:19 pm
Teachers should explain to their classes that there is an ongoing debate, describe the positions of both groups and the logic behind them, and use this as an example to illustrate how different interpretations of the facts can lead scientists to different conclusions.