Pluto not a planet? why?

Question

What did they decide classifies a planet, lol did they just think it would be to much for school kids to memorise all the planets if there were over 20

Answer 1

Certainly rhe worry that the numbers could get out of control very easily, if Pluto remained a member of the planetary club was a major factor in the way the IAU came to a decision. We have (and Ceres has) been here before in fact, 150 years ago,

The problem in debating this is that most people don't have a clear idea of how many objects we now know to exist in the Solar System and the pressures that this creates for a better classification system.

It is by no means as simple as Planets, then Dwarf Planets, then SSSBs (Small Solar System Bodies).

Did you know there are three "asteroids" that are currently classified as both asteroids and comets? They managed to avoid the obvious problems that that creates by creating the new Category of Small Solar Systen Bodies and putting both asteroids and comets in it.

2060 Chiron (not the same as Charon) is one of these three objects in the outer solar system. Discovered in 1977 by Charles T. Kowal, it was the first known member of a new class of objects now known as Centaurs, with an orbit between those of Saturn and Uranus.

Did you know about Centaurs? Did you know there are asteroids that lie between Saturn and Uranus? I didn't.

Have you heard about Trojans? plutinos? twotinos? or cuberanos? Scattered Disc Objects? Oort Cloud Objects? I hadn't.

I didn't find out about any of these till this last week. These are all new categories of objects which have had to be introduced to classify the enormous variety of new discoveries being made about SSSBs and the expansion in our knowledge of our Solar System neighbours.

Here is something else I learned. Sedna is an Oort Cloud Object and when at its furthest from the Sun (its aphelion) is 975 AU (1 AU = 93 million miles) away from the Sun. In comparison Pluto at perihelion (closest to the Sun) is 29.658 AU and at aphelion is 49.305 AU

i.e. Sedna gets up to 20 times as far away from the Sun as Pluto does when it is at its most distant from the Sun. Big place, the Solar System, isn't it?

We now know of some 1000+ Trans-Neptunian Objects of which Sedna is but one, and if they had have let Pluto remain a planet there was a strong case for other TNOs to be included. Xena is larger than Pluto for example.

The basic probem Pluto has and had from the outset is that it is smaller than 7 moons in the Solar System: Ganymede, Io, Europa and Callisto (the 4 Gallilean moons of Jupiter) Titan (Saturn's largest moon) Triton (Neptune's largest moon) and our own Moon, all of which were discovered before Pluto.

Heirarchical thinking that Planets "ought" to be bigger than Moons and "size-ism" prejudice doubtless played a part in the recent IAU decision, But only a minor part. Mercury is smaller than the two biggest moons, Ganymede and Titan and it didn't get downgraded, did it?

From the way some people have reacted. anyone would think the IAU were out to "get" poor defenceless little Pluto and the discussion is clouded by anthropomorphic sentiments as a result, Sentimental attachment is hardly a good basis for scientific classification.

So: whilst there is understandable and widespread dismay at Pluto being demoted in status, people really need to understand the reasons the IAU had to grapple with definitions and categories at this time:

(1) in 1930 we knew of just one body lying beyond the orbit of Neptune. Now we know of more than 1000

(2) we are discovering asteroids at a rate of 5000 a month

(3) we now know of 200+ extra-solar planets orbiting 170+ other stars, some of which we now know to have asteroid belts

It is conceivable the IAU may create more categories in the future in the light of more discoveries, The moment we find an extra-Solar System planet with extra-terrestrial life on it, for example, I would expect Habitable Zone Planet to be a new category and only Earth and Mars of our local 8 planets to be in it.

We already have the distinction between a terrestrial planet (the inner 4 planets) and a gas giant (the outer 4 planets) and are assessing new extra-Solar-System planets in the light of that distinction and a new category name for the informally-named "hot Jupiters" (i.e. large planets orbiting near to their star at less than 1 AU distance) of which we know several, may not be far away,

As science expands its knowledge, it needs more concepts and categories with which to describe and classify that knowledge, That is perfectly normal and should neither surprise nor alarm us, Or cause anyone to denounce scientists as idiots.

Creating new categories and reclassifying known objects in the light of them has happened before: in the 19th Century when the number of planets was pruned from 11 to 7 out of concern that being consistent and admitting other, newly discovered bodies to the planetary club that were similar to the ones they chose to kick out instead would have meant the number of planets could rapidly start to escalate and mushroom out of control,

To understand what is going on now, it helps to understand what went on then,

The number of bodies in the Solar System known to astronomers has been burgeoning for a long time now, but the general public seems unaware of this, given the way people blithely talk of Ceres (discovered 1801) Charon (discovered 1978) and Xena (discovered 2003) having "just been discovered",

There was a similar definitions crisis in the early 19th century and again in the mid-19th Century as the number of known objects in the Solar System started to grow and grow,

By 1807 the 8 Solar System bodies known to classical astronomy (the Sun, the Earth, our Moon and the 5 classical planets known from antiquity, Mercury, Venus, Mars, Jupiter, and Saturn) (1 star, 6 planets, 1 moon) had grown to 26. Uranus was found in 1781 making 7 planets. There were 4 Jovian moons, 7 Saturnine moons and 2 Uranian moons, 14 in all

And then there was the discovery of the first four asteroids. These were 1 Ceres on January 1, 1801, 2 Pallas on March 28, 1802, 3 Juno on September 1, 1804, and 4 Vesta on March 29, 1807,

What were astronomers to call these new objects? They weren't moons as they rotated around the Sun, so they had to be planets, didn't they? As there was, initially, no other category but moons or planets to put them in.

After 2 Pallas was discovered though, Sir William Herschel (the discoverer of Uranus) coined the term "asteroid" meaning "star-like"), in 1802.

But Ceres was meantime assigned a planetary symbol, and remained listed as a planet in astronomy books and tables (along with 2 Pallas, 3 Juno and 4 Vesta) for about half a century until further asteroids were discovered.

So we now had 1 star, 11 planets and 14 Moons, the beginnings of a distinction between major and minor planets and a sense of unease as to what we would do if more asteroids were discovered as the first four were all disappointingly small in size, so did they really belong in the planetary club? (Similar doubts were expressed about Pluto, right from the outset in 1930,)

38 years pass and then in 1845 the asteroid 5 Astraea is discovered and on September 23, 1846 the planet Neptune and a mere 17 days later on October 10, 1846, Neptune's moon, Triton. (We now have 1 star, 12 Planets 15 Moons and 1 non-planetary Asteroid.)

The pace of discovery then starts to really hot up. Four more asteroids in nine months: 6 Hebe on July 1, 1847, 7 Iris on August 13, 1847, 8 Flora on October 18, 1847, and 9 Metis April 25, 1848

Then on September 16, 1848 an 8th moon of Saturn called Hyperion is discovered,

Plus a further 6 asteroids are found in just over two years: 10 Hygiea on April 12, 1849, 11 Parthenope on May 11, 1850, 12 Victoria on September 13, 1850, 13 Egeria on November 2, 1850, 14 Irene on May 19, 1851 and 15 Eunomia on July 29, 1851.

And on October 24, 1851 a 3rd and a 4th moon of Uranus: called Ariel and Umbriel were discovered.

So now we had 42 objects: 1 star 12 planets 18 moons and 11 asteroids. If the latest asteroids were all to be regarded as planets, making a total of 23 planets (and 10 Hygiea was bigger than 3 Juno, just like Xena is bigger than Pluto), it was likely to start getting silly (by 1868 the number of asteroids was to rise to 107 and Victorian schoolchildren would have needed a massive 115-word mnemonic to remember all the names).

The unease grew to a crisis, a redefinition was clearly necessary and an inevitable decision was taken to regard all 15 asteroids as a separate category from planets and Ceres, Pallas, Juno and Vesta were kicked out of the planetary club, just like Pluto has been kicked out now.

There are some clear parallels between the situation in the 1850s and the situation now, Four under-sized runts had obtained planetary status, with seemingly more to follow as they were discovered, creating an overwhelming feeling among astronomers that the currency would be devalued if all these further objects were to then be automatically awarded planetary status. So they cried Whoa! And called a halt. And created a new category, Just like the IAU has now done,

SO HOW MANY OBJECTS HAVE WE GOT IN THE SOLAR SYSTEM NOW?

Stars: 1

Planets: 8

Moons: over 80 known moons of the dwarf planets, asteroids and other small solar system bodies.

(The asteroid 87 Sylvia has 2 moons for example as does the Kuiper Belt Object KBO 2003 EL61.)

AND another 162 moons orbiting around planets: Mercury has none, Venus has none, Earth has 1, Mars has 2, Jupiter has 63, Saturn has 56, Uranus has 27, Neptune has 13.

Kuiper Belt Objects: over 800 (all discovered since 1992).

Trans-Neptunian Objects: over 1000 (includes the 800+ KBOs) i,e, there are 200+ in the Scattered Disk and the Oort Cloud.

Asteroids: Hundreds of thousands of asteroids have been discovered within the solar system and the present rate of discovery is about 5000 per month. As of July 23, 2006, from a total of 338,186 registered minor planets, 134,339 have orbits known well enough to be given permanent official numbers. Of these, 13,242 have official names.

Current estimates put the total number of asteroids above 1 km in diameter in the solar system to be between 1.1 and 1.9 million

So you can see

(a) why some definitions are needed and why reclassification is necessary

(b) how totally unaware of the state of scientific knowledge the general public is and how uninformed people are when they get excited at tales of "3 new planets being discovered" and wonder if there might perhaps be more where those came from,

Finally, these issues need to be seen in the context of the 205 extra-solar planets we now know to exist and the asteroid belts that have now been detected in some of those stellar systems,

Consistency being a desirable thing to achieve in science, whatever definitions and categories the IAU now adopt, they need to be applicable to every star with other objects in orbit around it, throughout the entire universe, That is the context in which Pluto's status is now being discussed,

SO, TO SUM UP: Pluto should not be a planet, nor should it be just another TNO or small solar system body, It has been given a status of dwarf planet, intermediate between these two extremes and that is how it should now be seen.

Answer 2

The decision was voted upon in Prague on 26 August this year - only a few days ago. Some 2,500 plus astronomers turned up, and the International Astronomical Union held the vote something like eight in the morning or something, when everyone was either just getting up or hung over and having a lie in or something.

Point being, the vote was passed among maybe 4% of the attendees, and the vote was made to strip Pluto of its rank as a planet.

To understand why they'd make such a stupid decision, you'd have to understand that there are two opposed camps of astronomers, both of which should really get a life. The Pluto vote was taken because Pluto staying a planet was the baby of one of the camps, and the other camp - the Dynamicists - weren't asked for their opinions on the matter.

So in the end, the decision to drop Pluto as a planet was made because of petty - minded, vindictive, snitty jealousy. Nothing more.

In fact, the "rules" governing what makes a planet a planet mean that, technically, there are no planets. The rule that a planet has to have an orbit that does not intercept other bodies is bad science, because every single planet's path crosses any number of asteroids, comets and other objects. And Earth's path crosses with that of the Moon twice in each lunation.

The universe can't be changed with a vote. Science should always override fashion and politics.

And Pluto is /still/ a planet, until something comes along and knocks it out of the sky.

Answer 3

Pluto has been put in a New List of Dwarf Planets . The scientists had a choice between expanding the List of Normal planets from 9 to 13 or to remove Pluto . They did the easier thing . And since this does not affect any Nation /Community ,this change went through .

Answer 4

Ha! They DECIDED that Pluto is now classified as a dwarf planet because they are finding other dwarf planets in the same gravitational pull as Pluto is in ...I suppose with Neptune or one of the other planets that are larger around that area of the solar system. I don't like the idea myself. But as we get better and better with our technology things are bound to change. There are also a couple of planets ...I can't name off hand right now....that have moons that we didn't know about just a few years ago. Imagine that! As far as the icy rock idea...Jupiter is the same thing..does that make it a comet, cause that's what comets are made of.

Answer 5

The main reason was that the International Astronomical Union reclassified the meaning of the word "planet" so that, to be a planet, a celestial body has to orbit a star or stellar remains; have sufficient mass for it's gravity to overcome rigid body forces and ensure that it's shape is fairly spherical; not be massive enough to start thermonuclear fusion in it's core; and have an orbit that has a clear "neighbourhood", i.e. not go within that of another body.

Pluto failed the final criterion as it's orbit enters Neptune's orbit for part of it's cycle. It is now classed as a Dwarf Planet, as are it's moon Charon, the new discovery at the edge of the solar system and the asteroid Ceres.

Answer 6

well alot of it has to do with the size and the material of the figure

for example: you couldnt call the sun a planet because its a star, a yellow star, that means its around the mid point of its life and in maybe another 5000 years it will either explode in a supernova or fade out and die as a black dwarf...one of those two deaths, im not really sure because different stars have different life spans and changes and ways to die...one of those two will come into affect though...and a planet cant die in a supernova or as a black dwarf because a planet cant die at all cause it isnt alive in the first place so the sun could never be classified as a planet

i would say chemistry has a good bit to do with what helps classify something as a planet too

and the sun will die in years to come...it will be the end of the world as we know it but at least we wont be around to see it

Answer 7

Because a few Fuddy Duddies said so, however there is now an underground movement in Science Circles to get all this recinded! There are petitions being drawn up and a lot of Scientists are calling the Fuddy Duddies, Fuddy Duddies.

Let see what happens!

Give it another few months and let's see if the SAVE THE PLANET PLUTO movement succeeds or not!

Answer 8

As we learn more about the universe, we adapt. We know more about Pluto now than we did when it was first discovered. You can get sentimental if you wish, but what is a planet? Pluto doesn't match common criteria for a planet very well, and when they settled for a definition of a Planet, Pluto didn't qualify. It's smaller than our moon. It's part of the Kuiper belt.

The universe is what it is, and astronomy tries to describe it as good as it can. Textbooks and mnemonics will have to adapt.

Answer 9

they decided pluto doesnt have enough characteristics as a planet after they discovered other orbits in space with same characteristics as pluto. pluto is a large icy rock thats round. so they decided that wasnt enough to be a planet becuase then other "rocks" would also be a planet, but i guess to make things easier they decided to leave pluto as a planet but they are thinking of adding another 3 planets with similar characteristics as pluto.

Answer 10

Pluto's not a planet cause it's just a peice of space garbage that got caught in our Sun's gravitational pull.

It's a cold barren rock in space that only rotates around the sun once every 2000 years.

Answer 11

the scientists decieded on a list of rules to define a planet and if it breaks them the planet is not a planet. pluto breaks the rule about not crossing the orbit of another planet so it is classified as a drawf planet not a planet.