Pluto would still be a planet if they hadn't discovered the other rocks now wouldn't it?

Question

i have answered the WHY IS PLUTO NOT A PLANET question at least 7 times ( size and lack of a discrete orbit ) BUT THIS IS THE REAL REASON they have known about the size and orbit for some time.

BUT THE REAL REASON FOR THIS QUESTION IS TO 'MAYBE' STOP A FEW PEOPLE FROM ASKING !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

WAKE UP sleepy - if they hadn't ... ( is this complicated - prior to rocks Pluto=planet now Pluto=not planet )

Answer 1

I would agree with you that is the fear that consistency would require the IAU to admit large numbers of other similar-sized rocks to the planetary club if Pluto had have remained a member of it, that was the principal reason for it being blackballed and shown the door at this time.

The identical situation has happened before in the 1860s when the number of planets was reduced from 12 to 8 and the asteroids 1 Ceres, 2 Pallas, 3 Juno and 4 Vesta, which had been members for over 50 years, were all kicked out and a Second Division was hastily created to house them in. Then as now.

EXECUTIVE SUMMARY:

Pluto was downgraded for much the same reasons as 1 Ceres, 2 Pallas, 3 Juno and 4 Vesta were initially classified as planets on discovery and then, 50 or more years later, demoted from planetary status in the 1860s, and the number of planets then fell from 12 to 8 as a result.

There are several parallels between the two situations, worth noting. We really have "been here before".

(1) they were all felt to be disappointingly small but despite that were accepted as planets ... AS

(2) there was no other category to put them in, when discovered, as they were the first of a new "breed" of objects to be found, and it wasn't realised at first there were any others like them.

(3) it was predicted there would be a "missing" planet where Ceres was found (by the Titius-Bode Law of planetary semi-major axes) (which had gained hugely in credibility when Uranus was found in 1781 at almost exactly the distance from the Sun that the Law suggested another planet, if there were one, would be found.)

Similarly Pluto's existence was surmised from gravitational "wobble" in the orbit of Neptune and astronomers then hunted for years for a missing planet that would fit the bill.

When Ceres (in 1801) and Pluto (in 1930) were finally found and found roughly where they were anticipated to be, it almost inevitably made the planet-seekers convinced that it was a planet they had found: i.e. they were predisposed to considering it as a planet, given it was a planet for which they had been hunting for some years.

(4) after they were discovered, a lot of further similar bodies were then discovered and if the first of their kind had have remained as planets, the case for admitting growing numbers of other such bodies would have been overwhelming and the numbers of planets would, it was feared, rapidly have soared "out of control".

(5) so a new category (asteroids, then and dwarf planets now) was invented and defined and the demoted ex-planets placed in it.

THE STORY IN FULL

Pluto was reclassified two weeks ago at a meeting of the International Astronomical Union in Prague, in a new, different category (dwarf planet) of Solar System objects from the one it previously was classified under,

What we have just witnessed in Prague is an exercise in scientific classifiation of the objects this branch of science studies, i.e. bodies in the Solar System and other extra-solar systems.

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?

So; whilst there is understandable 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: And they are all basically to do with new rocks being found everywhere we have looked.

(1) in 1930 we knew of just one body lying beyond the orbit of Neptune. Now we know of more than 1,000

(2) we are discovering asteroids at a rate of 5,000 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

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,

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 12 to 8 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 reassessed,

TAILPIECE

I am surprised the IAU did not act sooner. It is a guess but I think the asteroid belts found around the stars Tau Ceti and HD 69830 were the clincher, that pushed the IAU into action,

Tau Ceti, a G8 spectral type star similar to our Sun, 11.89 years away from us was discovered in 2004 to have an asteroid belt at least 10 times as massive as our own.

HD 69830. an orange dwarf star in the constellation Puppis, 41 light years away, was found in 2005 to have an asteroid belt about 25 times as massive as our own, and in 2006 to have three Neptune-sized planets in the habitable zone,

Concepts with which to classify and map the range and diversity of objects in these neighbouring star systems were clearly going to be needed.

Answer 2

I've been saying that Pluto should not be a planet for many years (well, at least 10 - when i was in grad school, maybe more like 15 - when i was in college) because it isn't like any of the other planets in orbit or composition. I can't remember when the first kuiper belt objects were discovered, but we knew in the 90s that Pluto was more like a kuiper belt object than anything else.

At least since I started teaching college astronomy 9 years ago (probably since before then) I always told my students that we really can't make a decision one way or the other until we know more about Pluto and the other kuiper belt objects. Now that we've found several large KBOs, it makes sense to reassess Pluto's status as planet. So I kind of agree with you. But Pluto's status as a planet had been in question for a long time before now.

Answer 3

pluto is not a planet because pluto orbits the sun, is round, does not have an isolated orbit (a bunch of other similar bodies have similar orbits.), and is not a satellite it is defined as a dwarf planet. this does not change anything about the solar system or pluto. it just corrects the mistake of classifying pluto as a planet initially.

i have been waiting for this since i was about twelve. i feel somewhat satisfied. i knew that pluto didn't fit the pattern set by the major bodies in the solar system so it was an anomaly. it just felt illogical and "out of place". this was the right thing to do, believe me. i don't understand why so many are having such a problem with this.

i don't know how long this will drag on tho. many planetary scientists are not satisfied that the definition is not rigorous enough.

http://www.iau.org/fileadmin/content/pdfs/Resolution_GA26-5-6.pdf

Answer 4

Yeah, I guess so.
Otherwise, they wouldn't have defined it as a planet in the first place.

Answer 5

Why is everybody so ignorant?

Answer 6

what is your main question?

Answer 7

probably so