Do you think we should have considered Pluto as a planet in the first place?

Answer 1

With hindsight, no, but it is understandable that it was so classified,

I was interested in Fermi of Borg's argument that they were convinced there was a planet there, so when they found something, then "obviously" (given that idee fixe governing the search) when they finally found it, they were predisposed to the view that what they found must be a planet.

And as it was the first KBO to be found, they had no concept that there might be others and no such category as Kuiper Belt Object into which to place it as an alternative,

I say I find that interesting because the exact same thing happened to 1 Ceres, the first object to be found between Mars and Jupiter in 1801.

(a) its existence was predicted (using the Titius-Bode Law proposed in 1766) * (see footnote)

(b) as 1 Ceres was the first asteroid to be found, they had no concept that there might be others and no such category as asteroid into which to place it as an alternative, The term wasn't even coined until 1802 when 2 Pallas was discovered and both were felt to be rather disappointingly small.

When 1 Ceres was found and in almost exactly the position where Bode's "Missing Planet" was predicted to be (as Uranus had been) it was understandable that the searchers felt vindicated and it was declared to be a planet and given a planetary symbol.

As were 2 Pallas, 3 Juno and 4 Vesta. And they remained as planets until the 1860s when they were downgraded again, like Pluto has just been.

So the historical parallels are considerable.
With hindsight, 1 Ceres should not have been called a planet either, but it is understandable that it was so classified,

THE SIZE ARGUMENT

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?

THE CONTEXT

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

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,

A GRADUAL PROCESS OF DISILLUSIONMENT

HOW CERES CAME TO BE DOWNGRADED AND THE PARALLELS TO TODAY,

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 1 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.

TO SUM UP

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,

THE BIGGER PICTURE

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 has now been reassessed,

In an initial burst of enthusiasm, we made a mistake. We have, on reflection, realised that, and we have corrected it. It wasn't the first and it won't be the last mistake we make,
.

Answer 2

As there were no other like objects out there, it was only logical that Pluto was included as the 9th planet.

Now we have discovered many other like objects, it is obvious Pluto is not related to the other 8 planets, and was not part of the same process that formed the 8 planets.

Good question - it is nice to have soemthing other than those bleating heart questions "why did they do it to my poor Pluto", usually put forward by people who never usually give the planets a thought.

Well done.

Answer 3

Probably not. But you have to consider the circumstances surrounding its discovery:

Astronomers first theorized the existance of Uranus and Neptune by observing slight perturbations in the orbits of other planets. Having had such success, they began to think that perturbations in Neptune's orbit indicated yet another one further out. One of the astronomers involved in such predictions was Percival Lowell, who went so far as to suggest an exact location for what he called 'Planet X'.

As it turns out, all such calculations were erroneous. Pluto's mass is too small to cause any measurable amount of perturbation in Neptune's orbit, and astonomers of the time had grossly misestimated Neptune's mass. But back to the story...

Lowell spent much of the rest of his life looking for Planet X, and founded Lowell Observatory which continued the project after his death. When they did find an object out there, part of the reason why they named it 'Pluto' was to be reminiscent of (at least the initials) of Percival Lowell himself.

So you can see what happened... a group of people were LOOKING for a planet. They found something, so they decided that it must BE a planet. They HAD to make the declaration quickly lest someone else lay claim to the object before them. So they kind of jumped the gun a bit. If some other group had tracked it down it probably would have been just labelled as another of our solar system's oddities, being the small chunk of rock that it is.

That's my opinion anyway, for what it's worth. Make up your own mind! ( :

Answer 4

It was probably the right decision at the time, on the limited information available, though you would have thought that the experience with Ceres Pallas Juno and Vesta would have made them, think twice about the wisdom of rushing into it.

Perhaps what they should have done is have a period of candidate status. During which further thought and discussion could occur, before confirming the decision.

But definitely the right decision to demote Pluto now. Should have happened earlier, I suggest.

Answer 5

The astronomers at the time went with the information they had, based on all evidence Pluto fit their definition of a planet, so YES

Answer 6

This is a much better question than most of the Pluto questions that are circulating on the site.

I tend to agree that it was a mistake but a forgivable one, under the circumstances. We are entitled to change our minds in the light of new evidence, I think. How else is science to progress?

Answer 7

Bob G were given it proper. Astronomers were actively searching for a planet, so even as "something" replaced into discovered, it replaced into immediately referred to as a planet. the hunt began even as someone calculated "perturbations" contained in the orbit of Neptune (we now know those perturbations do not truly exist). depending on the size of perturbations and on the concept that Pluto replaced into responsible for them, it replaced into idea that Pluto had to be massive (honestly higher than Earth). We now know that that's largely a million/6 the mass of our Moon. With the telescopes attainable on the time, no longer something else replaced into detected that some distance away. for sure, Pluto met the definition that we use in the present day (even in spite of the reality that that definition did not formally exist in writing back them) of "having cleared its orbit". We now know that there are countless different "stuff" in that area (a number of it even higher than Pluto). The definition (having cleared...) did not formally exist on paper, besides the undeniable fact that it were used contained in the 1850s and 1860s to demote 4 planets (Ceres, Vesta, Juno, Pallas). even as more desirable proper telescopes grew to develop into considerably availeble contained in the 1840s, astronomer began gaining knowledge of all kinds of stuff contained in the area shared with the help of those 4 planets. for sure, this replaced into no longer a area controled with the help of a unmarried planet, for this reason all the stuff there shaped a sparkling type of gadgets: the minor planets.

Answer 8

No but we didn't know any better. We weren't aware of how many Plutos there were out there and had a poor idea of how the solar system formed.

Answer 9

Yes. It's spherical and it orbits around the sun. It's a planet. I have no idea what the sun's light reaching a heavenly body has to do with something being a planet as long as it has a complete orbit around a star.

Answer 10

yes because by make pluto not to beconsidered a planet would confuse many people and have them mixed up plus this info;(a) is in orbit around a star or stellar remnants;
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape;
(c) is not massive enough to initiate thermonuclear fusion of deuterium in its core; and,
(d) has cleared the neighbourhood around its orbit.

Answer 11

If everything that is known now was known when it was found, it probably would not have been called a planet, then there wouldn't be a mess to clean up.