Is it fair that Pluto is now considered as not part of our solar system?

Question

Pluto is still there - no one can take it away. It was found, even though its very far away. Its still a planet. Why decide on sumthing like that?

Answer 1

Since when did the words "our solar system" only refer to "the planets in our solar system"!?

Pluto remains part of the former large collection of objects but not part of the latter elite set of objects.

It is one of three members of the new "dwarf planets" classification, along with Ceres and Eris (as "Xena" is now to be known), as a result of recent IAU decisions in Prague.

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 three 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:

(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

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 Eris (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 Saturnian 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 Eris 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

Dwarf Planets: 3

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,

IN CONCLUSION

Pluto should no longer be considered as a planet, but neither should it be thought of as just another TNO, KBO or small solar system body, It has been given a status as a dwarf planet, intermediate between these two extremes and that is how it should now be seen and come to be accepted by people.

Recent questions have suggested Pluto is to be known as 134340 in future. That is a gross distortion. It is to be known as 134340 Pluto, as listed in the Minor Planet Centre. A system that was started back in 1801-2 with the designation 1 Ceres and 2 Pallas.

It is not losing its name nor is it being stripped of it, any more than it is being kicked out of the Solar System. Such over-simplifications are misinformation and seem designed to elicit knee-jerk emotional reactions from people who do not know the facts. by keeping them in ignorance of them. The way to counter such over-simplifications is to lay the facts before people and that I have tried to do.

Answer 2

Debates have raged for a long time on what is considered a planet. Scientists are still arguing over whether Pluto is or should be a planet. However - to keep from having to "accept" asteroids, traveling meteors that decide to stick around, and other space objects as planets, the International Astronomical Union set standards. Pluto doesn't measure up. There has been debate for years as to whether it did, since sometimes it is on our side of Neptune, and sometimes on the other. Since Pluto orbits both the sun and Neptune it isn't really a planet. Why decide? To keep from having to replace the list. Would you really want to have to memorize 276 planets ... or 8?

Answer 3

Pluto is a part of the solar system. With the advances in imaging technology, and with humans able to see and explore father in to space than ever before, we are discovering more and more objects, that may be able to be considered planets. A new definition for a planet had to be reached in order to deal with these new discoveries.

A planet is now something that has enough mass to allow gravity to pull it in to a sphere. Pluto fits this criteria, however the new definition of a planet is that it has to have it's own seperate orbit around the sun. This is where Pluto loses it's planetary status. Pluto intersects the orbit of Neptune. In reality it could be considered a moon of Neptune, but no one is ready to make that claim yet.

Pluto is a planetoid in our solar system along with several other bodies, one of which Ceres, falls between Mars and Jupiter.

Answer 4

It is still part of the solar system, no one is denying its existence. However, if we never looked at science after classification than the world would be one messed up place. People believed for a very long time that the sun and the planets went around the earth, if we never revisited that classification that is what we would still be learning. Science is not exact, and as it develops we have to leave room for further or different ideas, otherwise it is pointless. Fair is not really the issue. I am sure Pluto isn't offended.

Answer 5

Pluto is still a part of the solar system. The only change was that the IAU finally came up with a definition of "planet." Pluto, like other small bodies that do not clear their orbit of other bodies, fails to meet the criteria for a planet under that definition.

There are thousands and thousands of non-planetoid bodies in the solar system, though, including Pluto.

Answer 6

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

the international astronomical union defined three terms "planet", "dwarf planet", and "small solar system body". this does not change anything about the solar system or pluto. it just corrects the mistake of classifying pluto as a planet initially. i don't know how long this will drag on tho. many planetary scientists are not satisfied that the definition is not rigorous enough.

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 a dwarf planet.

i have been waiting for this since i was about twelve. i feel somewhat satisfied. this was the right thing to do, believe me. i don't understand why so many are having such a problem with this.

look here:
http://en.wikipedia.org/wiki/Pluto
http://en.wikipedia.org/wiki/Kuiper_belt

Answer 7

Pluto, also known as 134340 Pluto, is a dwarf planet in the solar system, orbiting 29 - 49 AU from the Sun. About a fifth the mass of the Moon, Pluto is primarily composed of rock and water ice. It has an eccentric orbit that is highly inclined with respect to the planets and takes it closer to the Sun than Neptune during a portion of its orbit. Pluto and its largest satellite Charon have often been considered a binary system because they are more nearly equal in size than any of the planet/moon combinations in the solar system, and because the barycentre of their orbits does not lie within either body. Two smaller moons named Nix and Hydra were discovered in 2005. Pluto is smaller than several of the natural satellites or moons in our solar system (see the list of solar system objects by radius).

From its discovery by Clyde Tombaugh in 1930, Pluto was considered the ninth planet from the Sun. In the late 20th and early 21st century, many similar objects were discovered in the outer solar system, notably 2003 UB313 (nicknamed "Xena") which is slightly larger than Pluto. In August of 2006 the International Astronomical Union (IAU) redefined the term "planet", and classified Pluto (along with several other trans-Neptunian objects and the asteroid Ceres) as a dwarf planet.[1] Pluto is also classified as the prototype of a family of trans-Neptunian objects.[2][3] After the reclassification Pluto was given the minor planet number 134340.[4]

Pluto's astronomical symbol is a P-L monogram, ♇. This represents both the first two letters of the name Pluto and the initials of Percival Lowell, who had searched extensively for a ninth planet and who had founded Lowell Observatory, the observatory from which Tombaugh discovered Pluto. Besides its astronomical symbol Pluto also has an astrological symbol. Pluto's astrological symbol resembles that of Neptune ( ), but has a circle in place of the middle prong of the trident

Answer 8

It's still part of our Solar System. It's just that it has so much more in common with the Kuiper Belt Objects than it does with the other 8 planets, it makes more sense to change its classification. but in the end it doesn't matter what label we put on it. Pluto just is!

Answer 9

"Fair"?

I have no idea how the concept of "fairness" applies.

The reason that the definition of planet is under debate is that our knowledge of the solar system is growing and changing.

Ever hear of the planet Ceres? No? For 50 years, Ceres was called a planet; now it's known to be the first of a class of objects usually called asteroids.

Pluto is now considered to be the first known member of a class of objects called Kuiper-Belt objects.

Ceres was "demoted" to avoid hundreds or thousands of new "planets" from the asteroid belt. Pluto is being demoted to avoid hundreds or thousands of new "planets" from the Kuiper Belt.

Answer 10

It is still part of our solar system. It's just not classified as a planet any more. Pluto is very close to the same size as its moon and they orbit each other.... so which is the moon and which is the planet?

Answer 11

No one is counting Pluto out of our solar system, it is just that rules that would make it a planet would add 4 additoinal planets, besides, and likely over a hundred very soon. You have to draw the line somewhere.