Should Pluto remain a planet, or should it be forgotten?

Question

Its all over the news, and its stating that pluto was demoted giving us 8 planets instead of nine. What are your thoughts on this?

What about the fact that the gov't will have to republish millions of dollars worth of books for schools

Answer 1

Those aren't the only alternatives. The best response for schools is to use the recent events as an example of how science sometimes needs to reclassify the objects it studies as it develops and progresses and makes new discoveries and finds new evidence and makes more accurate and detailed observations and measurements.

Books go into new editions and websites are generally more up to date anyway.

Pluto hasn't gone anywhere, it just got reclassified as a dwarf planet along with Ceres Charon, Xena and a dozen others, mostly Trans-Neptunian Objects like Charon and Xena, but three of them are, like Ceres, asteroids lying between Mars and Jupiter.

There is understandable dismay at Pluto being demoted in status but people 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 to be in it.

We already have the distinction between terrestrial planet (the inner 4 planets) and 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 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", And given how one Yahoo answerer recently confidently asserted that Ceres, Charon and Xena were all "newly formed"!

(I wish people wouldn't make up astronomical theory on the hoof like that! The gullible will only go and repeat such Malapropisms as gospel truth!) (Gossip-tell truth would be a more apt description,)

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,

Answer 2

Everyone seems to think that the Solar System is smaller now, but in reality we have 3 additional celestial bodies to remember although not as planets.

Along with Pluto's "demotion", several asteroids were "promoted" to Dwarf Planet, including the asteroid Ceres that was considered a planet at one time.

To be honest I do not think that demoting Pluto is in anyway different to redefining Ceres to an asteroid. The original grounds for Ceres' reclassification was the discovery of other asteroids that comprised the asteroid belt between Mars and Jupiter. This mirrors Pluto's reclassification due to larger objects found in the Kuiper Belt beyond Neptune.

I don't think it will ever be forgotten.

Answer 3

Never. Pluto was a PLANET and will remain a PLANET. I want like-minded people to oppose the IAU and sign a petition at http://pleasesavepluto.org/. Let us not let them win easily.

Answer 4

I think poor Pluto shd remain a planet. So what if its small? It has a satellite which means that its a planet.

Answer 5

Neither. It should not be a planet, but it should not be forgotten.

It's important: it's the first Kuiper Belt object to be discovered and the nearest to us. It's going to be very important in understanding the structure and history of our solar system.

Answer 6

I say why bother..let the damn thing still be a planet...just because there are dwarf homosapians this does not mean that we do not still consider them human...ya know.....these r my thoughts...

on another note..this is planetary profiling...we should not judge because of one planets size or color in relation to the other planets size ect...ect...ect

Answer 7

why not read the whole articles (if they are actually publishing the whole story)
There are three other rocks out there bigger than pluto and orbiting the sun but they have never been considered planets.
So you either redefine them or correctly define pluto.
Frankly, I don't see how its going to affect anybodies life.

Answer 8

"Forgotten?" It hasn't been declared non-existent, just reclassified. It's still one of the most significant bodies in our system.

Answer 9

pluto should remaina a planet. that's what i remember learning in high school.

Answer 10

We can't forget it. It's still up there.