Is Neptune next? why is Pluto being scrubbed???

Question

are there any other planets further out than pluto that are not included in the solar system?? is it right to scrub a planet from the solar system, or is it just that scientists cant be bothered gathering info on it coz its too far away? so why not just have earth as the only listed planet and be done with it?

Answer 1

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.

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. The discussion is also clouded by the fact that most people seem to be blissfully unaware of the number and variety of objects we now know there to be in the Solar System and similarly unaware of the fact that we (and Ceres) have been here before, 150 years ago.

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,

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

There are many other planets further than Pluto including its moons. The reason Pluto is not a planet anymore is based on the fact that many other moons are larger than Pluto and new planet definitions were created and Pluto did not fall into these definitions so it is not considered a planet any longer. In addition Scientist can collect information on Pluto and for this reason they decided it no longer met the specifications for being a planet and Scientist currently can look out onto at least one or two other Solar Systems of planets which may and most likely contain life of some kind.

Answer 3

Pluto fits several ways into not being a planet:
1. It has no atmosphere
2. It is very small (which is why it has no atmosphere)
3. Its orbit does not lie on the solar plane, it is at an angle
4. it has a very obvious ecliptical orbit (it actually gets closer to the sun than neptune at some points)

Due to these characteristics it is more like a large asteroid than a planet.

In comparison, Mercury which is slightly larger than pluto does have a very faint atmosphere, and has a normal planetary orbit.

Answer 4

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Pluto may lose planet status
By Stephen Cauchi
March 10 2003





The solar system, we've been told since primary school, has nine planets. But a fierce debate raging among astronomers could mean that number being revised to as low as eight or as high as 12, if not more.

Quaoar, Varuna and Ceres are names students may one day start learning alongside Mars and Venus. And tiny Pluto may become an asteroid or "Kuiper-belt object" rather than a planet.

Gibor Basri, an astronomer at the University of California, is about to submit a controversial proposal to the International Astronomical Union (IAU), which has naming rights to space objects, that would increase the number of planets to 12. The IAU has a working group considering the definition of "planet".

"It's something of an embarrassment that we have no definition of what a planet is," Professor Basri told his campus newspaper, Berkeley News. "People like to classify things. We live on a planet; it would be nice to know what that was."

Professor Basri said that recent discoveries of large asteroids in the Kuiper belt, on the solar system's fringes, had tested the hazy definition of "planet". If Pluto, with a diameter of 2300 kilometres, was a planet, other similar-sized bodies in the solar system should be so regarded, he said. The 1300-kilometre Quaoar, discovered last year, was the biggest find in the solar system since Pluto in 1930.

According to Professor Basri's definition, a planet must orbit a star, not another planet, and it must be round. That means it must be 700 kilometres in diameter, when gravity moulds it into a sphere, or bigger. Smaller objects are potato-shaped.

Under his definition, the 900-kilometre asteroid Ceres, discovered in 1801, would become a planet, as would the Kuiper-belt objects of Varuna, discovered in 2000, and Quaoar.

"All the accepted, or putative, planets are round," he said in his proposal. "One can calculate the lower limit for this mass ... it is a little below the mass of Ceres, or objects less than about 700 kilometres in diameter. That seems a good place to draw the bottom line for planets."

But other astronomers, if not most, would rather delist Pluto than call smaller objects like Ceres planets. A New York planetarium in 1999 did not include Pluto in its display of planets, and the IAU was forced to deny rumours that year it would delist Pluto. But some academics, like Ross Taylor of the Australian National University, have already removed Pluto from planet status in their textbooks.

"Most astronomers now say there are eight planets," Professor Taylor said last year. "It's arbitrary ... you get into a real semantic sort of swamp. It's like trying to define life."

At the other extreme, Professor Basri says a planet can't be bigger than 13 times the mass of Jupiter. Because such objects generate heat and light, they should be called stars.

Professor Basri meets opposition here too. Geoff Marcy, a member of the Anglo-Australian planet search team at Siding Springs telescope - which has discovered 13 of these planets - says other factors need to be taken into account, including how the planet was formed.

"It's way too early to define a planet," he said. "Even though we have now found over 100 of them, these are still early days in planet hunting."

Answer 5

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 learned that pluto does not have the physical and orbital characteristics that fit the pattern set by the major bodies in the solar system when i was about twelve, and i have been waiting for this since then. believe me this was the right thing to do.

because neptune is round and orbits the sun in an isolated orbit it is a planet.

because pluto is round, orbits the sun with a bunch of other similar bodies with similar orbits, and is not a satellite it is a dwarf planet.

(1) A "planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.

(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.

(3) All other objects orbiting the Sun shall be referred to collectively as "small solar system bodies".


look here:
http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html

Answer 6

Pluto is not being "scrubbed". The New Horizons mission is still heading to Pluto and will fly by in 2015, sending back to Earth unprecedented close-up pictures of Pluto/Charon and its moons, as well as other data.

Answer 7

Because this debate's been hotly contested since the 30s. It's just the scientists wanting to get their way and demoting poor Pluto so some other dumb schmuck planet can get in.

I wouldn't worry. It's not official. No school texts will be changed to reflect it.

Answer 8

I think it is because a planets orbit cannot be affected by anything other than its central star, the sun. And Pluto was affected by neptune. Therefore it is not considered a planet.

Answer 9

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Answer 10

well,tha reason is cuz pluto is pretty far away,n accordin to tha scientists pluto is a bit too small to be classified as a planet(even after viewing thru their telescopes).some bunch of idiot scientists hav said that pluto is a bit too small to be branded a planet.no none of tha planets we knw at present r gonna be removed frm tha solar system cus most of them r pretty large in size(as compared to earth).tha size of pluto is said to be smaller than our own moon.

Answer 11

Neptune is not next, it's too big to be ignored. Pluto is just too small and it orbits it's own moon too. It's just a dwarf planet.