As I understand, the IAU has now described the asteroid Ceres as a Dwarf planet, along with Pluto and newly discovered Eris. In conversation I have found dissenting opinion on the spheroid shape of Ceres, as in "its not really that spheroid, and its too small for the category anyway". Anyone who can expound upon Ceres' spheroid shape and its internal differentiation? Any personal thoughts on the new classification of Ceres as dwarf planet?

Ceres has a mass of 9.5e20 kg, which would make it the 16th largest moon in the solar system if it were orbiting a planet. It's about 70% of the mass of Charon, which was almost deemed a planet by the initial IAU resolution.

It would be about the 7th largest known dwarf planet, after Eris, Pluto, 2005 FY9, 2003 EL61, Sedna, 2002 TC302 and Quaoar.

As far as roundness goes, it has a minimum diameter of 909 km and a maximum of 975 km. That's an oblateness of 7%. That's definitely less round that the rocky planets (generally less than 1%), but in the same ballpark as the gas giants (2-10%).

The question is not whether Ceres is round enough, but whether the general roundness of it's shape is due to gravity. After all, even very massive objects like Saturn can be spun out of "roundness" due to rotational velocity.

I'm not sure if Ceres passes this test. Saturn has an oblateness of 9% and it seems round enough, but Proteus (a moon of Neptune) has a 8% oblateness and doesn't seem round to me.

http://en.wikipedia.org/wiki/Proteus_%28moon%29

The only pictures we have of Ceres are very fuzzy (see link below). I would not be too surprised if it were demoted back to "minor planet" after the Dawn mission.

http://en.wikipedia.org/wiki/1_Ceres

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Some observers have found evience that Ceres is covered in part with clay, indicating that long ago it was covered in water. It also seems likely to me that Ceres may be more massive than Charon, which is also listed as a dwarf planet.

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Is it?

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I believe that the mass of Charon and Ceres are both known with some confidence. I could be wrong, though.

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According to Wikipedia, Ceres' mass is 9.5 × 10²⁰ kg and Charon's mass is (1.52 ± 0.06) × 10²¹ kg. Because Charon's mass can be measured accurately thanks to Pluto, I would think that the latter value is more accurate.

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When I search for current listings of Dwarf planets, I find only Pluto, Eris, and Ceres. I believe Charon is not listed because its a satellite, but there is the possibility that Charon and Pluto are binary planets. Which would likely upgrade Charon's status to dwarf planet.

As I understand it, the rule is, as long as the mass of the planet causes something near to Hydrostatic Equilibrium, oblateness is not an issue, because the general shape is still round, and oblateness is caused by rotation, and not mass.

I would think that a surface texture ratio (ie smoothness) would be a good indicator of hydrostatic Equilibrum in in such cases, as would internal differentiation. Ceres is believed to be internally differentiated with more massive materials at the core and less masive materials near the surface. Then you consider objects like EL61 which have certainly enough mass for hydrostatic equilibrium, but EL61 is highly elongated from extraplanetary impact (theorized) and a high rotation speed (4 hours). Could EL61 be classified as a dwarf planet?

Yes, it could. That's why they used the language "Hydrostatic Equilibrium", rather than saying an object has to be sperical or speroidal or whatever.

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