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Space NASA Science

Mass of Dwarf Planet Eris 27% Greater than Pluto 220

Posted by Zonk from the she-wants-a-bite-of-the-apple dept.
jcgam69 writes "When it was discovered in 2005, some thought Eris should be considered the 10th planet of our solar system. Everyone still considered Pluto a planet then. At first, Eris was thought to be slightly larger. Now — with the help of Eris' moon — Eris is known to be 27% more massive than Pluto. If Pluto had remained a planet to the entire community of astronomers, surely Eris would be considered the 10th planet."
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Mass of Dwarf Planet Eris 27% Greater than Pluto More

Mass of Dwarf Planet Eris 27% Greater than Pluto

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  • Haiku on a Distant Rock (Score:4, Funny)

    by Anonymous Coward on Thursday June 14, 2007 @05:57PM (#19512557)
    Poor lonely Pluto;
    No one loves you now but me.
    And Clyde Tombaugh [wikipedia.org]'s urn.

  • New Nmemonic (Score:5, Funny)

    by DTC ( 450482 ) on Thursday June 14, 2007 @06:00PM (#19512589)
    My Very Excellent Mother Just Serverd Us Nine Pizzas- Excelsior!

    • Re: (Score:3, Funny)

      by Wah ( 30840 )
      and post-plutpwnage it becomes...

      My Very Excellent Mother Just Serverd Us Ninja Excrement.
    • Yeah, but Pluto got voted out... so now.

      My Very Excellent Mother Just Served Us NOTHING!

      You know, Pluto had a good thing going until these stupid other transneptunian objects started to to clutter sky and make people turn on poor little Pluto. It's like being able exploit a flaw in a game. It works great for a while, but then a bunch of people do it and you're screwed.

    • The new mnemonic avoiding Plute and Eros, which aren't really planets, just for Slashdotters:

      Many Veteran E-users May Joke Slashdot Upsets Nerds

  • Hail Eris! (Score:5, Funny)

    by subl33t ( 739983 ) on Thursday June 14, 2007 @06:00PM (#19512597)
    All Hail Discordia!

    Hail yes!

    fnord.

  • What can I say... (Score:4, Funny)

    by setirw ( 854029 ) on Thursday June 14, 2007 @06:03PM (#19512629) Homepage
    ...our beloved ninth planet just got plutowned!

    • Re: (Score:2)

      by h2g2bob ( 948006 )

      our beloved ninth planet just got plutowned
      Not really. Pluto and Charon form a binary system. Together they outmass this upstart.
  • it's a planet. If it's orbiting a larger planet, then it's a moon.

    This is just a classification problem. In my company, the secretary takes care of that shit. WHY ARE WE wasting our time with this crap? I don't give a shit if some schoolkid has to memorize dozens of planets. That's between him and his teacher.

    • Re: (Score:2, Informative)

      by poopdeville ( 841677 )
      You're a member of the IAU? Otherwise, you must be using the Royal we.

      In any event, the "dwarf planet" classification is informative. Dwarf planets have sufficiently low mass that they have no managed to clear their orbital path from other massive objects. Their properties are very different, despite orbiting the sun and being round.

      Why use a cluttered ontology when a clean one can be designed?

    • Re:If it's round (Score:5, Interesting)

      by Pfhorrest ( 545131 ) on Thursday June 14, 2007 @06:50PM (#19513169) Homepage Journal
      it's a planet. If it's orbiting a larger planet, then it's a moon.

      What, no distinction between round moons and non-round moons?

      I think we need to have our system of classifications able to accurately distinguish between:

      - Bodies of sufficient mass that they would undergo fusion if of fusionable composition (stars).
      - Amongst those, ones which are of fusionable composition (active stars) versus those which no longer are (inactive stars).
      - Amongst non-stars, bodies which are of sufficient mass to be approximately round (major planets) versus those which are not (minor planets or asteroids)
      - Amongst planets, those which have an orbit centered on a star (regular planets) versus those which do not (irregular planets).
      - Amongst irregular planets, those which have an orbit centered on another planet (moons) versus those which do not (asteroids).

      Thus, Phobos and Deimos are minor irregular planets, and also moons (call them just "minor moons" since all moons are irregular planets); while similar bodies in the asteroid belt are also minor irregular planets, but are not moons but rather asteroids. Europa and Ganymede are a major irregular planets and also moons ("major moons"). Luna is a major moon. Eris and Pluto (if I understand the irregularity of their orbits correctly) are major irregular planets and also asteroids (or just "major asteroids", for all asteroids are irregular planets). Earth, Mars, etc are major regular planets, and schoolkids can memorize those and ignore the rest; for simplicity of terminology we can always assume "major" and "regular" unless specified otherwise, so "planet" alone refers just to bodies like those.

      There now, everybody happy? Pluto is a planet; it's even a major planet; however, it's an irregular major planet and thus not a "planet" simpliciter.

      • - Amongst non-stars, bodies which are of sufficient mass to be approximately round (major planets) versus those which are not (minor planets or asteroids)

        Er, scratch that "asteroids" bit, that was written in error.

        Also, it dawns on me that all non-stars are planets (though not planets simpliciter) by this system of classification, so, this line merely distinguishes between major and minor planets.

        On that note, it would probably also be useful to distinguish first between bodies at rest upon other bodies (like me and this computer) versus bodies in freefall (like all the forgoing bodies), for I'm uncomfortable with myself being classified as either a star or

      • I think we need to have our system of classifications able to accurately distinguish between: [classification snipped]

        Why? The actual physical and astronomical facts about the matter, given our contemporary understanding of astronomy, do not depend on such a classification at all. The classification of the celestial objects is not a matter of convenience, not of fact. No astronomical fact follows independently from the "fact" that body X is classified as a Y in your scheme. That is, the only facts tha

        • Re:Gah, cut it out (Score:5, Interesting)

          by Pfhorrest ( 545131 ) on Thursday June 14, 2007 @11:16PM (#19515015) Homepage Journal
          You are of course completely right that naming conventions per se tell us nothing about the physical universe. However, good taxonomies and naming conventions will allow someone to tell a lot about the physical attributes of something which has previously been examined and classified by someone else just be hearing it's name. For example, "lion" and "tiger" are two names which refer to very similar objects, but you wouldn't know that just by their names. Panthea leo and Panthera tigris, on the other hand, let you know that these are both subtypes of some object class Panthera, and if you know what that entails, then you'll know a lot about both of those objects. If I overheard that there's a wild Fubar on the loose, I'd have no idea what that was until it was explained to me (though by context I could guess that it's some sort of animal); however, if I overheard that a Panthera fubaris had escaped, while still not knowing what exactly that was, I'd know it was some sort of large carnivorous feline, and thus just by convenient naming, I'd be able to learn (and communicate) new information much more quickly.

      • Re: (Score:2)

        by Xtifr ( 1323 )
        > "What, no distinction between round moons and non-round moons?"

        Round moons are planets; non-round moons aren't. That was implicit, and no other distinction is needed. I basically agree with grandparent poster, and think that any system of categorization which claims that Mercury is more like Jupiter than it is Ceres is...utterly brain-dead.

  • So let 'em both in (Score:3, Insightful)

    by FlyByPC ( 841016 ) on Thursday June 14, 2007 @06:06PM (#19512691) Homepage
    Pluto is big enough to have a moon (okay, so Pluto/Charon is really a double planet). Eris is more massive than Pluto. Sounds like they should both get to (re)join the club. Why not?

    • Re:So let 'em both in (Score:5, Interesting)

      by ushering05401 ( 1086795 ) on Thursday June 14, 2007 @06:18PM (#19512827) Journal
      The funniest thing to me is that we are so fixated on the planet/not-a-planet debate. Let em both in, don't let either in...

      Both bodies will continue to be studied, and when the time comes, they will be exploited for their natural resources.

      This debate will only matter fifty years from now when we actually begin mining other planets and mining related laws discriminate between bodies with different scientific designations.

      Regards.

      • Re: (Score:2)

        by syousef ( 465911 )
        I couldn't care less if Pluto is classified as a planet or not. What I do care about is that the definition for a planet makes sense. The current one voted by the IAU is a joke. Dwarf Planets are not Planets (confusing and unscientific calssification), bodies orbiting other stars are not planets by definition. Therefore years of literature about extra-solar planets is made technically incorrect in one fell stupid swoop. If you're going to reclassify Pluto as something other than a planet, go for it, but the

    • Re: (Score:2)

      by Kelson ( 129150 ) *

      Pluto is big enough to have a moon (okay, so Pluto/Charon is really a double planet).

      Sure, but the asteroid Ida has a moon, Dactyl [nasa.gov], as well, so I'm not sure that's useful criteria for planethood.

      • Re: (Score:2)

        by arth1 ( 260657 )
        In my opinion, the solar system consists of what a visiting alien would notice:
        • One star, Sol
        • Two large gas planets: Jupiter and Saturn
        • Two medium ice gas planets: Uranus and Neptune
        • Two small rock planets: Venus and Tellus
        • Various rock debris mostly between the inner planets and the gas giants (including Mars and the other asteroids).
        • Various ice debris mostly outside the medium ice gas planets (including Pluto, Eris and the other transneptunian objects)

        Mercury and Mars are just too small to be counted (Ma

        • Re: (Score:2)

          by bytesex ( 112972 )
          Tellus ? Is that Terra, as in Earth ? Did I miss something ?

        • Re: (Score:2)

          by Ihlosi ( 895663 )
          Mercury and Mars are just too small to be counted (Mars is only around 10% of Earth's mass and 15% of Earth's volume).

          Both are close enough to the sun and large enough to be fairly noticable.

          It probably depends on what kind of planet the alien would find habitable/interesting/valuable. If their main interest lies in hot Jupiters, our solar system would get a "nothing interesting here, let's try the next one". If they're interested in the most massive objects, it would be "One sun, one smallish and one tiny

    • First, a quick response to your proposal: LOTS of things have moons. There are quite a few non-round asteroids (not big enough to gravitationally collapse) that have moons. In general, if any of us here in the peanut gallery have a proposed definition that sounds even vaguely plausible, it's a good bet that the professional astronomers have not only thought of it years ago, but also figured out solid reasons why it wouldn't work.

      Speaking of asteroids, I'd like to remind everyone that for most of the 19th

  • You see? You see? Your stupid minds...stupid! Stupid!!

    (Okay, so it's "Eris" and not "Eros". Sue me.)

  • Kuiper belt (Score:3, Insightful)

    by blind biker ( 1066130 ) on Thursday June 14, 2007 @06:10PM (#19512729) Journal
    The Kuiper belt, I am sure, contains still some surprises for us. Perhaps many surprises, and who knows, maybe some of them unpleasant. I wouldn't be surprised if Neptune one day grabs one of those rocks and launches it over here. That'll be lots of fun.
    • "The Kuiper belt, I am sure, contains still some surprises for us."

      Yeah, like finding Cthulhu there instead of the Pacific ocean. Then it won't be Neptune launching the rocks....

      (ok, go for the Uranus jokes now)

  • every one knows . . . (Score:3, Informative)

    by jd142 ( 129673 ) on Thursday June 14, 2007 @06:18PM (#19512817) Homepage
    That Mondas is the 10th planet. Duh.
  • .. the planet is defended by 5 lions.

  • Ah, astronomers... (Score:5, Funny)

    by UbuntuDupe ( 970646 ) on Thursday June 14, 2007 @06:22PM (#19512871) Journal
    Remember: just now they figured out which of Eris and Pluto is more massive...

    but they also know the internal density distributions of extrasolar planets that barely take up a pixel on the most powerful telescopes.
    • LOL, too true.

      With the mass of Eris and Pluto, it was a relatively high precision measurement (for astronomers anyway). For the internal density profiles of planets, it's not a direct measurement---it's modeling of the data to argue for consistency with various models. So, to put it more accurately, they just measured the masses of Eris/Pluto correctly; but for the extrasolar planets, they considered various models consistent with the data and showed which one is most likely.

      Generally the public does

      • Re:Ah, astronomers... (Score:4, Informative)

        by bdeclerc ( 129522 ) on Friday June 15, 2007 @03:34AM (#19516249) Homepage
        Actually, while the measurement of the extrasolar planets with "known" masses is likely to be considerably less precise than the mass measurements of Eris & Pluto, it is by no means as "based on models" as you imply.

        Those planets for which actual density has been determined are in a special class (or at least, special from our viewpoint):
        These are planets which (a) pass in front of their star as seen from earth, thereby causing a slight dimming of the starlight seen from here, and (b) have sufficient mass to cause a measurable red/blueshift in the spectrum of their parent star.

        The dimming of the light gives us their apparent diameter relative to their parent star, the duration of the dimming gives us a pretty accurate idea of the diameter of the star, the red/blueshift gives us their mass relative to their parent star and the orbital period gives us, to a considerable degree of accuracy, the mass of their parent star.

        These four parameters are actual measurements, so since we can derive the actual mass & diameter of the planet from these four parameters quite easily, the average density value we derive is as close to a direct measurement as we'll get.

        For planets which do not eclips their star as seen from earth, only lower limits to their mass can be determined (so the planet has to be "at least x earth masses") and even those do indeed depend on stellar modelling to determine the mass of the star, but since without the eclipses, there is currently no way to determine the diameter of said planet, there is no realistic way to determine the actual density of the planet anyway.
    • I'm not a big astronomy guy, but could this be because extra-solar planets are the current "sexy" thing to look at? It seems that the "sexier" stuff gets more funding, ergo, let's half-guess some crap up about Alpha Unicron?

  • Everyone? (Score:2, Informative)

    by KenAndCorey ( 581410 )

    Everyone still considered Pluto a planet then [in 2005]

    What are you talking about? I haven't considered it a planet since I took astronomy in the early 90's. Of course the public didn't have a clue, but a lot of astronomers knew Pluto shouldn't be considered a (regular) planet.

  • Mistaken assumption (Score:5, Interesting)

    by aafiske ( 243836 ) on Thursday June 14, 2007 @06:53PM (#19513203)
    I think the mistake in the logic here is assuming that Pluto was kept a planet because it had a certain mass, or orbit, or whatever. Pluto was kept a planet because of tradition, in essence. If it were found today, I don't think it would be considered one. So no opening of the floodgates for every hunk of rock that has some number that measures larger than Pluto.
    • While the basic gist of your comment is correct, I think the mistake in your logic is assuming Pluto is still a planet.

  • Dwarf Planet is so Politically Incorrect... (Score:5, Funny)

    by sconeu ( 64226 ) on Thursday June 14, 2007 @07:00PM (#19513301) Homepage Journal
    Pluto and Eris prefer the term "Gravitationally Challenged".
    • Eh, get with the times, "... challenged" is so 20th century. Nowadays they prefer the term "differently gravitated".
  • Eris dies.
  • 27% Greater than Pluto

    I don't believe any statistic about a planetoid named after the Goddess of Disinformation.

    "There's lies, damn lies, and statistics...and then there's Discordians."
  • What difference does it make whether there are nine things we call "planets," or eight, or ten, or a hundred, or a thousand? I suppose "planet" is a less special term if there's a lot of them, but we already know there are hundreds out there already; so what if there's a hundred in our solar system, or only fifty, or whatever. Seriously, what difference does it make to anything?

    The physical and orbital characteristics of Pluto and Eris will remain the same regardless of whether we call them planets or min
  • It goes around our sun? Check
    It's somewhat large? Check
    It even has it's own moon? Check

    So why is this not considered a planet? I never understood why we demoted Pluto.

  • If you really want to get picky on classification, we probably shouldn't put the outer planets in the same category with Earth. Earth & Pluto are more alike than Earth & Uranus. Earth & Pluto are both round, solid masses of various minerals. Uranus and the other outer planets are just enormous masses of gas with no solid surface and no rocky minerals.

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