88 Largest Objects in the Solar System

By Sean Carroll | March 30, 2007 8:59 pm

Every known object in the solar system larger than 200 miles across. (Via Cynical-C.) Here are Eris (formerly Xena), Pluto, and 2005 FYg (informally “Easterbunny”); check out the rest.

Now tell me that Pluto is a planet. Wherever it may be. Or don’t.

By the way, my Caltech colleague Mike Brown, who is the guy who causes all this trouble by discovering all these extra planets, has just been awarded Caltech’s Feynman Teaching Prize. Congratulations, Mike!

  • Dr William Dyer

    Should one consider Pluto a planet? My answer is Splunge.

  • Carl Brannen

    That was a truly cool link.

  • http://blogs.discovermagazine.com/cosmicvariance/john John


  • http://trinifar.wordpress.com/ Trinifar

    Why does Firefox 1.5 crash when I go to that link? Anyone have a clue?

  • http://thechocolatefish.blogspot.com/ Yvette

    I’m using Firefox 1.5 and it loaded just fine.

    And thanks for the link Sean! I still remember being fascinated by the first discoveries of KBOs when I was in 3rd grade (not quite as weird as it sounds, it was in the kiddie version of National Geographic), and marvel at how what was the fantastic has become so commonplace we’ve usurped a planet for it. Makes me excited to think about what we’ll discover in the next dozen years!

  • http://lablemminglounge.blogspot.com/ Lab Lemming

    Looks like a great argument for demoting the smallest terrestrial planet, which is hiding between half a dozen moons.

  • http://www.amara.com/ Amara

    The IAU could have given the situation more thought than they did, however. What they created is truly a monster. These new dynamic definitions now demonstrate that Earth is not a planet, Mars is not a planet, Jupiter is not a planet, and neither is Neptune.

    I would have preferred them to leave it alone, but now we can think what to do to fix the mess in the next IAU meeting in 3.5 years. Here is one idea by Mark Sykes.

  • http://andyxl.wordpress.com/ Andy Lawrence

    I voted in Prague, blogged about it, and have been pursued by the save-pluto banner waver Laurel Kornfeld since. This beautiful picture does indeed lose Pluto in the mix. Its number eighteen. My growing personal feeling is that we don’t need a definition of planet at all. Its not like agreeing the format of co-ordinates, or data transfer protocols. Does the IAU define the difference between a Seyfert galaxy and a quasar ? Of course not. How would that help ? In Prague, like many other people, I basically voted to stop a fruitless angels-on-pins debate.

    I am seriously tempted to frame a proposal that we should not have a definition of planet. Sounds like William Dyer agrees.

    And very well done Mike Brown ! Well deserved.

  • http://www.amara.com/ Amara

    A Seyfert galaxy is considered a galaxy. However, a dwarf planet is not considered a planet. Some consistency would be nice. Astronomers have discovered some >200 extrasolar planets, but the IAU definitions only apply to our Solar System (!!) And where are the brown dwarf stars in that scheme? If astronomy instructors are unable to describe the bodies in the universe to their students with those definitions, and astronomers and planetary scientists cannot use them either, then what was the point?

    At the very least, given the mess that exists now with those IAU definitions, astronomers and planetary scientists should be using this opportunity to describe to the public the wonderful observations that we have, and why this became an issue in the first place.

    Moreover, some very good physics, geophysics, orbital mechanics can be taught in the process, instead of backhanded remarks about how silly the situation is. Why not use this opportunity to explain that the Earth has NEOs in its vicinity, and Pluto has plutinos in its vicinity, Mars has two captured asteroids for moons, Jupiter didn’t exactly clear its orbit because there is belt of broken-up objects in resonance with it called the Main Belt. We can describe what are the differences between classical KBOs (cubewanos), resonant KBO (and plutinos), short-period comets. centaurs, and Scattered Disk objects. We can describe that we don’t know how large are the largest planets or how small are the smallest brown dwarf stars and why. We can describe the role of hydrostatic equilibrium in spheroid shapes, what are the dynamical conditions that puts an edge on the Kuiper belt, why Neptune migrated to its present position, and how the Scattered Disk is formed.

    There’s some fantastic material here for education. Many in the much smaller community of planetary scientists have that attitude to use this debate as a springboard for education in their public interactions. I hope that astronomers can adopt that attitude too.

  • amateur night

    > These new dynamic definitions now demonstrate that Earth is not a planet,
    > Mars is not a planet, Jupiter is not a planet, and neither is Neptune.

    As Hal Levison explains, and any smart high school student can understand:


    Earth is a planet, Mars is a planet, Jupiter is a planet, and so is Neptune.

    Pluto and Ceres are not planets.

  • http://www.amara.com/ Amara

    I appreciate that Hal used the opportunity for education. Thank you, Hal. Please notice that he is not using the IAU definitions. Thank you , IAU for giving us a mess.

    You can hear Mike Brown and others speak about this issue, on the Jim Lehrer News Hour. At least two of the people interviewed said that they thought it was a balanced report. Most of it was recorded during the DPS meeting last October in Pasadena.

  • http://magicdragon.com Jonathan Vos Post

    The acronym for these bodies, the 88 Largest Objects in the Solar System , in order of decreasing diameter, breaks down when names do not yet exist [*], but begins [Sun, Jupiter, Saturn, …] =


    This is hard to pronounce, althouth the substring:
    “CIMETEP” is pronouncible for Callisto, Io, Moon, Europa, Triton, Eris, Pluto.

    This is exactly the sort of thing about which Isaac Asimov used to write delightful essays.

    Of course, I find part of the Periodic Table to to prouncible, sort of:

    ScTiVCrMnFeCoNiCuZn is rendered as:
    Scatty Vickerman Feconey Cousin.

    So, kids, start memorizing “SJSUNEVMGTMCIMETEP…” because it WILL be on the final exam…

  • http://americansector.wordpress.com Josh

    Why limit yourself to 200 mi? Check out size comparisons of everything from solar systems to atoms at Universcale

  • http://predelusional.blogspot.com/ Stephen Uitti


    Pluto is a planet.

    (you asked.)

    The IAU could have given the situation more thought than they did, however.

    The IAU did give the situation more thought. Then, at the last minute, they voted on something else. Given a 700 km limit, there are something like 27 planets. With double planets, there are 29. I’d be just as happy with 100. My ten year old has to memorize the 50 states and their capitals. Not a big deal.

    Then, the IAU should get it’s act together and come up with a lower limit for the size of a moon. At the moment, Saturn has, what, billions? And the Earth has thousands of moons that are tracked.

    A really nice image.

    Perhaps your Firefox has run out of RAM. Do you have a swap partition turned on?

  • http://laurele.livejournal.com Laurel Kornfeld

    This is indeed a beautiful picture, but why does it have to be twisted into a statement against Pluto’s planethood? It is interesting that Eris turns out to be only marginally larger than Pluto. When Eris was first discovered, it was thought to be a lot bigger.

    I agree with Stephen Uitti that the IAU decision was not what was originally discussed and also see no problem in having even 100 planets in the solar system if all those objects meet a sensible definition.


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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .


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