I had assumed that 1 Ceres was still considered an Asteroid since it orbits in the asteroid belt and has the same origin as the other asteroids.

But I noticed that on wikipedia they say: "Ceres is a 'dwarf planet', and may no longer be classified as an asteroid."

Wiki sites IAU comments at http://www.iau2006.org/mirror/www.ia...0603_Q_A2.html that say:
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Q: What is Ceres?

A: Ceres is (or now we can say it was) the largest asteroid, about 1000 km across, orbiting in the asteroid belt between Mars and Jupiter. Ceres now qualifies as a dwarf planet because it is now known to be large enough (massive enough) to have self-gravity pulling itself into a nearly round shape. [Published reference for shape of Ceres: P. Thomas et al. (2005), Nature 437, 224-227. Dr. Peter Thomas is at Cornell University.] Ceres orbits within the asteroid belt and is an example of a case of an object that does not orbit in a clear path. There are many other asteroids that can cross the orbital path of Ceres.


Q: Didn’t Ceres used to be called an asteroid or minor planet?

A: Historically, Ceres was called a “planet” when it was first discovered (in 1801) orbiting in what is known as the asteroid belt between Mars and Jupiter. Because 19 th century astronomers could not resolve the size and shape of Ceres, and because numerous other bodies were discovered in the same region, Ceres lost its planetary status. For more than a century, Ceres has been referred to as an asteroid or minor planet.
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Is it NOT correct to say:

Ceres is still the largest asteroid even though Ceres is also a 'dwarf planet'. Pluto is a Kuiper Belt Object (KBO) even though it is also a 'dwarf planet'.

???

-- Kevin Heider

It IS correct say that. Ceres is still an asteroid (or like the IAU says, a minor planet). Pluto and Eris ARE Kuiper belt objects.

Otherwise the term "dwarf planet" would be contradictory: If they're not members of the belts, then why they're not true planets?

EDIT: Argh, now I read the IAU Q&A... I think it's wrong. "Asteroid" means "minor planet" (despite that Wikipedia claims otherwise). When the Minor Planet Center assigned Pluto a minor planet number, they mentioned that objects can have dual classifications (there are a few asteroid-comets). So Ceres is a minor planet, as is Pluto. Ceres it is a dwarf planet, but it is also an asteroid (unless asteroids = small solar system objects sans comets).

__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

Hum,
The term `minor planet` is banned.
All references to it should be removed from the textbooks, public buildings and temples;
The term `small solar system objects` is now preferred.
The term `Asteroid` can be used, but not in public debate or scientific papers - it is best used in pubs for tittle-tattle.

However, Ceres is technically not a small solar system objects because it is a dwarf planet.

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`Irony` actually does mean `metal like`...

Also, remember that the wikipedia article is the collective opinions of everyone who participated in writing it, not any sort of authority on the nomenclature of the solar system.

As I understand it, asteroid is still a useful descriptor for objects that are part of the asteroid belt and NEAs, as it represents a dynamical grouping of bodies that share similar orbital and physical characteristics. Specific names for different groups exist, such as Atens, TNOs, Jupiter Trojans, Centaurs, etc. so it's probably best to use those descriptors, rather than the catch-all SSSB.

the term 'SSSB' replaces the outdated and confusing term 'minor planet', but does not affect the names for more specific dynamic groups.

Thus, the terms SSSB, dwarf planet, and planet tell us something about how massive the object is, from small irregular bodies, to rounded bodies, to bodies large enough to sweep out the debris of planetary formation. The specific names for dynamical groups tell us where the objects are, and in some cases where they came from or what they're made of. Planets can also form dynamic groups, such as the terrestrial planets and gas giants.

So Ceres is both a dwarf planet and asteroid, and is sometimes even counted as a terrestrial planet. Pluto is a dwarf planet, TNO, KBO, and plutino. Eris is a dwarf planet, TNO, and SDO. Both Pluto and Eris also belong to a new and unnamed group of eccentric, inclined, long-period ice dwarfs. (Wouldn't that be a fun bit of terminology, the 'EILPIDs'!)

To me, this new classification system makes a lot of sense, and avoids being extremely arbitrary. There are going to be borderline cases where it's not exactly clear which groups a body belongs to. I see those are merely opportunities to refine the terminology, and don't see why they should doom the definition as a whole.

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audentes fortuna iuvat

The IAU Small Solar System Body Center, eh?

Since dwarf planets are also minor planets asteroids, the term "asteroid" includes both non-cometary SSSBs and dwarf planets. In other words, asteroids don't form a subset of SSSBs.

__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

As a TOP1000 Wikipedia contributor who has focused on asteroids I know that.

I don't count comets as minor planets, nor does the MPC. In a sense it is odd since KBOs are minor planets but comets like Halley which is believed to have originated from there, isn't. Although the term "SSSB" is clumsy, it hopefully makes this more clear.

Then we agree.

Not actually. 'Minor planet' is synonymous to 'asteroid' (or if you don't count TNOs as asteroids, then MP = asteroids + TNOs). I think it's highly unlikely that the term 'minor planet' will be removed from use.

Then why the term "dwarf planet" had to be invented (planetoid, although historically synonymous to asteroids, would have been much better)... To be fair, if Resolution 5B had passed, they would have formed a subset of planets. And it is a nod to Pluto and its kin. Not a planet, but a dwarf planet anyway.

There's nothing dynamical in terrestrial/gas giant classification. It is based purely on physical properties, but happens to split the groups nicely in dynamical sense in our Solar system since the gas giant's didn't migrate as much as in some planetary systems.

Ceres is not a terrestrial planet by any means.

The members in the unnamed group are dwarf planets and are located beyond Neptune. Circular, non-inclined orbits are allowed, so "EILPID" would be a misleading term.

I like the three-tier classification system planet/dwarf planet/SSSB. What I don't like is that the term "asteroid/minor dwarf" isn't a true subset of SSSBs. But I understand it would highly impractical to manage dwarf planets separately.

__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

As far as I knew, the new category was for bodies with eccentric inclined orbits with a period >200 years. Did that part of it not make it past the draft resolution?

I kinda liked the word I made up... It wouldn't be any more misleading than many of the other terms used in astronomy, though... There's precedent! XD

Oh, and I know Ceres isn't a traditional terrestrial planet, that's why I said sometimes. so there!

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audentes fortuna iuvat

It does seem that Ceres would be a very interesting destination for an unmanned probe. Do any of the space agencies have plans to send anything to check it out?

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Gone Sailing

Yes. Dawn

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Fiction has to be plausible. Reality is under no such constraint.

I believe DAWN will be visiting in a few years time: http://www.dawn-mission.org/mission/index.asp

Cool - just have to wait 9 years to see how it works out...

Thanks for the link

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Gone Sailing

Has it started fusioning or something? :-P

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http://amssolarempire.blogspot.com

Despite the IAU Q&A cited, there is still some dispute as to whether Ceres remains an asteroid or not.

It is definitely a dwarf planet. The question is whether a dwarf planet can simultaneously be an asteroid. Do the definitions overlap?

The definition passed in August divided bodies other than the Sun in our solar system into three - planets, dwarf planets and small solar system bodies (SSSBs). The resolution stated: "All other objects³ except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies"". Note 3 was: "These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies."

OK, if SSSBs only include 'most' of the asteroids, then there must be some asteroids that are not SSSBs. The eight planets were never asteroids, so that only leaves the three dwarf planets as possible asteroids (or TNOs). Hence - is Ceres still an asteroid?

Is Australia an island, continent, or country?

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http://amssolarempire.blogspot.com

For which I ask:

Name the 1st Asteroid discovered? Ceres or Pallas?

Name the largest Asteroid? Ceres or Vesta?

*IF* Ceres is truely no longer an asteroid because it is spherical then those two very basic questions have new answers!

-- Kevin Heider

Hum,
my take on it is that it is an asteroid. (though the term is now outdated)
But by being classed as a dwarf planet it excludes it from being a SSSB.

(ie, the earth is classed as a planet so it excludes it from being a SSSB)

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`Irony` actually does mean `metal like`...

I agree.

I disagree. The term Asteroids still define non-planets originating from the region of the asteroid belt. The Asteroid Belt and Kuiper Belt do exist.

I disagree. Then why was Pluto and Eris assigned a Minor Planet (now SSSB) number? I believe that 'dwarf planets' are a subset of SSSBs, and thus will never be major planets.

-- Kevin Heider

Dwarf planets are not SSSBs.

After the definitions of a planet (1) and a dwarf planet (2) comes the definition of Small Solar System Body:

(emphasis mine)

__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

But that does not require that 'dwarf planets' be excluded from the list of Minor Planets (SSSBs). Since Pluto and Eris have been assigned SSSB numbers, I think the IAU intends to include 'Dwarf Planets' as SSSBs.

Only Major Planets and satellites will not receive SSSB numbers.

-- Kevin Heider

No, that means some minor planets/asteroids are not SSSBs. Pluto and Eris have been assigned minor planet numbers. There's not such thing as "SSSB number" (comets have different designation schemes).

Like mentioned earlier, it reads most, not all.

Pluto and Eris received minor planet numbers for practical reasons: Ceres already has one and some of the largest numbered TNOs will most likely be reclassified as dwarf planets.

__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

Hum,
perhaps...
But its possible that they didn't think of that consequence when they created the new class of Dwarf planet.

http://en.wikipedia.org/wiki/Small_solar_system_body

If the IAU really intended to include 'Dwarf Planets' as SSSBs, then it could be assumed that the definition of planets is a also subgroup of SSSBs.

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`Irony` actually does mean `metal like`...

"All other objects..." says rather explicitly that objects excluding planets, dwarf planets, and moons are SSSBs.

Never say never... If the Resolution 5B had passed, "dwarf planets" and "classical planets" would have formed two categories of objects called "planets". Since it didn't pass, "dwarf planets" are not real planets. That vote was the one which actually demoted Pluto.

__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

Splitting the solar system into three groups (planets, dwarf planets, SSBs)...

Poor Titan.

Honestly what's the need for the term dwarf planet. I think if the definition were just based on orbital characteristics it would make things easier.

Planet=orbits primary body (star, brown dwarf, free floater), and has dynamically cleared its zone.
In our solar system: 4 terrestrial planets, 2 gas giant planets, 2 ice giant planets

Debris=orbits primary body (star, brown dwarf, free floater), and is dynamically insignificant.
In our solar system: an assortment of asteroids, ice dwarfs, and comets

Satellites=orbits secondary body (planets, debris).

So IMO, Ceres is an asteroid...a Main Belt Object to be specific.

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This space is for rent.

True. But that is why I wrote MAJOR Planet. I left myself wiggle room.

OK. I thought the IAU was replacing all future references to Minor Planets with SSSBs. But you are right active comets do not receive Minor Planet numbers.

So Ceres is a 'dwarf planet', asteroid, 'minor planet', and aka big rock in space.

If the term 'minor planets' is still used that means we still have 136k minor planets instead of 136k SSSBs.

Now I can go play with 1 Ceres at Wiki and get yelled at.

-- Kevin Heider

I can't see any reason to stop calling Ceres an asteroid. Are they going to renumber all the others now?

I'd agree with those who find the "dwarf planet" class a little odd. There are seven mere satellites larger than most (all?) dwarf planets - known and unknown, and they are all incomparably more interesting.

Why classify by orbit at all? Surely such namings belong to publicity not science.

Ceres remains an asteroid and other asteroids will not be renumbered (what would be the point with that)? Vesta, Pallas, and Hygiea were potential planets in the original draft resolution so they may get eventually promoted.

Why not? After all, the term 'planet' refers to a substellar (and sub-brown dwarf) object which orbits a star. So the term is fundamentally related to dynamics.

An example of more "scientific" classification scheme could be a classification based on separate physical and orbital properties (circumstellar planemo ~ 'planet', circumplanetary planemo ~ 'large moon' etc.).

__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman

Yes!

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Since everybody is into reclassifying things, why not reclassify Saturn's moon Enceladus a comet nucleus. Some of the pictures of it taken by Cassini, it certainly shows the characteristics of a comet nucleus.

They like to say that if Pluto were discovered today it would never have been considered a planet. Well, if we had no knowledge of Jovian type planets and Jupiter was discovered today, would it be a planet or a failed star?

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I'm not a scientist, but I play one on the internet.
http://www.rrac.org

The plumes of Enceladus are most likely generated by internal heat. In comets, the Sun's warmth makes them active. So, it's not a comet nucleus. Even worse, it orbits a planet, which makes it a satellite, no matter how comet-like it would be (c.f. the irregular satellites which may be very comet-like in composition and origin).

They're right.

Maybe not a planet but not a failed star, either (Jupiter is not nearly massive enough).

__________________
Science is a way of trying not to fool yourself. The first principle is that you must not fool yourself, and you are the easiest person to fool.
-- Richard Feynman