Reported in BA Blog: Eris more massive than Pluto

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Poor poor Pluto...

Well, the opposite would have been quite a surprise. If Eris is only 30% more massive it can't be much larger (as volume increases rapidly as the radius changes + gravitational pressure which shrinks the size).

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I don't think this is exactly right. the mass of the Eris and Dysnomia combined can be found with this method.

Dysnomia is much fainter than Eris, so it is reasonable to expect that it is much smaller, hence much less massive than Eris. In the case where the mass of Eris >> mass of Dysnomia, the orbital period will give an accurate approximation of Eris' mass. But if Dysonmia is fainter because it has a much lower albedo, and all the mass they're attributing to Eris is actually equally divided between the two bodies, then neither may be as massive as Pluto. That is almost certainly not the case, but I wonder if that's a remaining question mark hanging over their conclusion. Maybe I should read their paper and find out.

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...might as well forget the "Pluto Petition" then. :-\

{sigh}

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Well, if somehow Dysnomia's mass was a considerable fraction of Eris', the latter should be seen orbiting the center of mass... Based on the orbital period of 16 days it must be much farther than Charon is from Pluto.

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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.
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Here's the original Hubble press release. More from Mike Brown's website.

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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

ToSeeked, by a matter of minutes apparently.

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Ten planets, works for me.

/rudegesture IAC

Eh, not again. The only two sensible possibilities were 8 and dozens of planets. The IAU did the right decision.

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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

So the number of planets was determined by a plurality of eggheads who can't count beyond the number of digits on their hands?

I agree personally, the main "reason" for not using a definition that would include more planets is that there would be "too many." Boo hoo, I can't count to twenty!

I think the proper course of action would have been to call any spherical object in orbit around a star a "planet," and then splitting the category into two sub-categories: Major planets and minor planets. The major/minor designation could be made by the "clears the area around it" argument. After all, the word planet just means "wanderer." I feel like the IAU just wanted to demote Pluto to make headlines and draw attention to themselves.

"Eight" sounds better than "dunno".

Come on, both Pluto and Eris are ridiculously tiny for planets.

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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

"Ridiculously tiny" is not a terribly quantitative criteria...

Me too. Planet of Sun = Pluto or larger.

Would that make the earth a double planet?

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No. Planet of Sun = Pluto or larger AND orbits the Sun.

"Pluto or larger" is also incredibly arbitrary. I'll clarify my opinion on the definition of a planet. The lower limit for the word "planet" should be the lower limit for what the IAU currently terms "dwarf planets." Then, separate the planets into two sub-categories (major and minor), depending on if they have cleared their neighborhood or not:

* Planet (Any object in hydrostatic equilibrium that is not a satellite of another planet)

- Major Planet (Has cleared its neighborhood)
- Minor Planet (Has not cleared its neighborhood)

Simple and far less controversial!

Yes, "Pluto or larger" is arbitrary.

But so is any other definition.

Thus, since any definition is arbitrary, we should arbitrarily choose a definition that does the least damage to existing nomenclature. "Pluto or larger" is therefore the ideal definition.

But what if a small "planet" is found that is only slightly smaller than Pluto? Does the definition change to "That new planet or larger"?