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Pluto and its biggest moon, Charon  (Source: NASA)
Pluto gets new classification: Plutoid

After being demoted from a planet to a dwarf planet by the International Astronomical Union (IAU) two years ago, the IAU has announced the term "plutoid" will be given to Pluto and similar dwarf planets.  Members of the IAU argued amongst themselves for two years, confused on how to classify dwarf stars like Pluto.  

Only dwarfs orbiting further than Neptune can be classified as a plutoid, and they must also circle the sun and be large enough to have their own gravitational field.  Pluto's permanent classification as a plutoid now means Neptune is the outermost planet in Earth's solar system; one complete orbit around the sun takes almost 165 years.

"Plutoids are celestial bodies in orbit around the sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit," said the IAU.

Pluto and Eris remain the only plutoids at the moment, but astronomers expect to find other small bodies that meet the qualifications to be a plutoid.

The controversy over Pluto's planet status has been strong for years, and the IAU-created plutoid classification most likely will not end the debate.  In fact, it is unlikely the debate regarding Pluto's status and what it should be classified as will never end, and defining it as a "plutoid" will only add fuel to the fire.

Many astronomers remain angry that Pluto, considered a planet for around 70 years, could have its status demoted so easily by the IAU.  Text book publishers and teachers must now begin to teach students that Pluto lost its planet status and is now a plutoid, along with describing the new classification.

The IAU has been the sole organization responsible for classifying all planetary bodies for more than a decade.



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But Wait;
By PapaBear on 6/13/2008 8:53:48 AM , Rating: 5
quote:
Only dwarfs orbiting further than Neptune can be classified as a plutoid


So what is Pluto classified as when it's orbit brings it between Neptune and the sun? Is it considered a planet for those few month?




RE: But Wait;
By mcnabney on 6/13/2008 9:45:01 AM , Rating: 2
That is a very good point. Using Neptune as a measuring stick is stupid. They should have kept the Dwarf Planet name and used it on any celestial object that has sufficient mass to round itself, does not orbit another planet (no moons), but does not have sufficient mass to clear its orbit. That would allow Ceres to finally have good label besides 'biggest asteroid'.


RE: But Wait;
By mcnabney on 6/13/2008 9:46:19 AM , Rating: 2
Because eventually we will find small planets around other stars and it would be nice if our definitions would apply there. Or maybe we will just make more arbitrary name up.


RE: But Wait;
By MozeeToby on 6/13/2008 2:02:55 PM , Rating: 2
So, what do we call it when we find a double planet that orbits about common center of gravity?

They can't be planets because they haven't "cleared their neighborhood" and of course they can't be moons because they don't orbit a planet.

They really need to think about creating some truely general definitions, instead of trying to come up with definitions that fit our cultural view of our solar system.


RE: But Wait;
By Digimonkey on 6/13/2008 2:15:19 PM , Rating: 2
Actually I don't think that's even a possible scenario. The planets have to have more mass than there moons to keep moons in their gravitational pull. If two objects have almost identical mass, but some how have intersecting gravitational fields, they would eventually separate from each other.


RE: But Wait;
By Screwballl on 6/14/2008 3:52:17 PM , Rating: 2
So what is to say that it is not possible to have another planet following the same exact (or close) path as Earth except on the exact opposite side of our sun? A place where the two gravities balance each other out and keep each other on opposite sides of Sol always. Until we get a telescope on/around Mars or Venus to keep an eye on that area, we will not know.


RE: But Wait;
By BMFPitt on 6/17/2008 2:22:20 PM , Rating: 2
And everyone whole lives there has a goatee.


RE: But Wait;
By prenox on 6/13/2008 3:12:48 PM , Rating: 2
I don't think that episode of Lexx was based in reality.


RE: But Wait;
By jbartabas on 6/13/2008 11:13:47 AM , Rating: 2
quote:
They should have kept the Dwarf Planet [...]


They have.
quote:

That would allow Ceres to finally have good label besides 'biggest asteroid'.


And Ceres is still a dwarf planet.

Plutoid is merely a sub-classification of dwarf planets.


RE: But Wait;
By jbartabas on 6/13/2008 11:09:00 AM , Rating: 3
No, you missed the point.

Pluto is a dwarf planet whatever its orbit is. The same way, Ceres is a dwarf planet, even with its orbit well inside Neptune's.

Plutoid is just a sub-category of dwarf planets: the transneptunian ones. At best, you could argue that Pluto is not a Plutoid at times, but not that it's a planet.


RE: But Wait;
By phazers on 6/13/2008 3:03:55 PM , Rating: 2
>"Plutoid is just a sub-category of dwarf planets: the transneptunian ones. At best, you could argue that Pluto is not a Plutoid at times"

Clearly we need to spend trillions to fix this mess - fly out to Pluto, attach giant rocket boosters, and kick it out permanently past Neptune. This violation of the new planetary definitions simply cannot be tolerated by any intelligent species, or so the Plutonians tell me.


RE: But Wait;
By Ringold on 6/13/2008 5:41:31 PM , Rating: 2
quote:
Plutoid is just a sub-category of dwarf planets: the transneptunian ones.


Others seem to still be fighting the planet label battle, but this is the part I see as stupid. It seems obvious to me; IAU wanted some positive PR for the unwashed masses, and thus battled for 2 years to get a special label just for ol' Pluto.

Their first mistake: The unwashed masses dont really care. Just geeks, but they got over it. This just reopens the issue.

Their second mistake: Never appease the unwashed masses.

I see the posts claiming its just a nice measure in creating further categories; whatever smoke screen makes the IAU feel good. Dwarf planet got the job done. It's shameless pandering. Considering it took them 2 years to get it done, sounds like some astronomers would agree.

I think, perhaps, they should've drawn the line at the frost line; isn't that just a wee bit past the asteroid belt? Then they could've distinguished between ice and solid planets, perhaps. But Neptune? Purely arbitrary, and with Pluto only being a Plutoid part-time, it shows.


RE: But Wait;
By Titanius on 6/13/08, Rating: 0
RE: But Wait;
By masher2 (blog) on 6/13/2008 11:56:58 AM , Rating: 3
> "I for one, because of Pluto's strategic orbit crossing paths with Neptune, will always classify it as a planet"

In other words -- because Pluto does something no other planet does...it's a planet? Come again?


RE: But Wait;
By Titanius on 6/13/2008 12:13:08 PM , Rating: 1
Not because of what it does, because of where it is located, sometimes closer to the sun than Neptune is.


RE: But Wait;
By jbartabas on 6/13/2008 12:27:26 PM , Rating: 2
Again, you totally missed the point: Ceres is much closer to the Sun than Neptune is, and it is not a planet. The distance to the Sun has no implication in terms of being a planet or a dwarf planet.

The distance to the Sun comes into play to distinguish between various types of dwarf planets. And the distance is defined in terms of semi-axis of the ellipse.


RE: But Wait;
By masher2 (blog) on 6/13/2008 12:27:36 PM , Rating: 2
Ceres is located much closer to the sun than Pluto and is also large enough to maintain a spherical shape. Why not call it a planet as well then?


RE: But Wait;
By Titanius on 6/13/2008 11:01:30 PM , Rating: 1
quote:
Ceres is located much closer to the sun than Pluto and is also large enough to maintain a spherical shape. Why not call it a planet as well then?


Why not?


RE: But Wait;
By werepossum on 6/13/2008 5:47:55 PM , Rating: 2
quote:
So what is Pluto classified as when it's orbit brings it between Neptune and the sun? Is it considered a planet for those few month?


Then we shall call it a planetino!

Ten (or more) planets would have been cool. Plutoids - not so much.

quote:
Members of the IAU argued amongst themselves for two years, confused on how to classify dwarf stars like Pluto.


Dwarf stars? I begin to suspect those "members" remain confused.


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