Become a fan of Slashdot on Facebook


Forgot your password?

The Sun's 10th Planet... Sedna? 636

dsanfte writes "While NASA remains intentionally vague, promising only a news conference Monday, The Australian has the details. The new planet, dubbed Sedna after the Inuit goddess of the sea, is 3 billion km further from the sun than Pluto, and is slightly smaller at 2000km in diameter. This discovery has apparently reignited the debate as to how big a solar object must be in order to qualify as a 'planet', but it is significant nonetheless."
This discussion has been archived. No new comments can be posted.

The Sun's 10th Planet... Sedna?

Comments Filter:
  • by Anonymous Coward on Sunday March 14, 2004 @01:27PM (#8561918)
    So why should we start counting an even smaller "planet"? Pluto gets grandfathered in, and that's it.
    • You exclusive club-types are all alike....

    • by WorkEmail ( 707052 ) on Sunday March 14, 2004 @01:36PM (#8562006)
      I say we put up a huge sign next to the Sun that says "You must be at least this big (insert huge red line) to ride this ride."
    • by c1ay ( 703047 ) on Sunday March 14, 2004 @02:20PM (#8562312) Homepage
      So where's the line between asteroid [] and planet []? IMO, Pluto [] should be labeled an asteroid since it's smaller than even our own moon []. Of course, there are also asteroids with moons but yet, they are considered asteroids, not planets. And what makes a comet [] a comet and not an asteroid, it's orbit? It would certailny seem that agencies like NASA that are so concerned with being precise in other areas could could come up with a more precise classification system.

      • Comets are snowballs; asteroids are rocks. Oversimplification, but you get the idea.
        • by Guppy06 ( 410832 ) on Sunday March 14, 2004 @04:54PM (#8563211)
          "asteroids are rocks"

          We should use this for the demarkation between "asteroid" and "planet." An asteroid is one big chunk of rock. A planet is a bunch of little rocks held together by their own gravity.

          If Pluto primarily orbits the sun and it's dense enough to hold on to an atmosphere from time to time, why shouldn't it be considered a planet?
          • by Martin Blank ( 154261 ) on Sunday March 14, 2004 @06:24PM (#8563799) Homepage Journal
            A large number of known asteroids are exactly that: clumps of rock weakly held together through their own weak gravitational forces.

            This incidentally leads to one of the fears of trying to deflect such an asteroid were it on a collision with the earth -- that it would simply fragment it and cause destruction on a wider scale.
            • by SEWilco ( 27983 ) on Monday March 15, 2004 @03:07AM (#8566319) Journal
              Yes, it would be so much better to just reshape the incoming rock into a long needle so we have destruction confined to only two tiny little spots, including the spot on the opposite side of the Earth.
            • by DunbarTheInept ( 764 ) on Monday March 15, 2004 @03:38AM (#8566447) Homepage
              The key to preventing an extinction-causing asteroid impact is simply to NOTICE it early enough and have a fast means to get a vehicle there. The reason the asteroid-defeating plans are so hard to create is that we have to wait until the asteroid is near us before we can reach it. By then it's too late. If we can affect it sooner, then exploding it into parts could work really well because the parts would be imparted with enough velocity to spread apart so most of them miss the Earth. Even if an object is headed to strike the earth dead-center, then you only need to deflect it far enough to move it a little more than one earth-radius of distance to the side by the time it gets here and that will make it miss.
              (You do need to go a little more than one earth radius because gravity will pull it in - you need to get it far enough out so it will at least slingshot around earth instead of striking it.)

              To put this in perspective, if the asteroid was blown up 40 days before impact, that would give us 960 hours for it to move. In 960 hours, an object can move an entire earth radius by going a mere 4.1 miles per hour. So as long as the explosion can impart a velocity of a little over 4.1 miles per hour perpendicular to the course of the asteroid, then the asteroid bits will veer far enough off course to miss. So exploding the asteroid and sending it's parts off in different directions *can* work, if your explosion is big enough to impart that much velocity, and (this is the hard part) you can get a vehicle carrying the bomb out there 40 days before the impacyt.)

              The best defense against such an asteroid is a better space program, with faster vehicles that don't require months of prep time to launch. That gives us the time for a simple solution to actually work.

        • I've got a couple possible solutions regarding the debate over labeling something a planet.

          1. Why not just call all solid [and liquid?] bodies "satellites" ? Asteroid, planet, moon, deathstar, they're all satellites from now on.


          2. Redefine "Planet" to mean: Any satellite of a star with enough mass to retain an atmosphere of any [detectable?] pressure.

          Rocks come in all sizes, so we ought to ditch the term or define it with respect to something as arbitrary as size.

          Our universe is hopelessly complex. Accept it. Part of life as a human is dealing with a world that impossible to fully predict or control. If we didn't have such a world, things would be far less interesting. (we might even be wishing that there would be issues to debate).
      • by Jesus 2.0 ( 701858 ) on Sunday March 14, 2004 @02:34PM (#8562406)
        Pluto should be labeled an asteroid since it's smaller than even our own moon.

        Frankly, I don't understand this line of reasoning. Why does it matter, with regards to whether something is a "planet" or not, whether that thing is bigger than, for example, our moon?

        And "asteroid"? Pluto is far, far larger than anything currently considered an "asteroid".

        Jupiter and Saturn both have moons that are bigger than Mercury. Do you not consider Mercury to be a "planet", either?

        What if Jupiter had a moon bigger than Earth? That's not unimaginable; would Earth then not be a "planet"? In fact, would then nothing be a "planet" except Jupiter, Saturn, Uranus and Neptune?

        I frankly don't see what's wrong with (something like) a "planet" being a non-star that's orbiting (directly) around a star. Sure, that makes for some seriously small "planets" relative to what we're used to, but at least it's not an arbitrary and useless definition like (no offense) yours.

        And anyway, if you want to add back in your preferred amount of arbitraryness, you can always start referring to "major planets", "minor planets", and so forth.
        • by mysticgoat ( 582871 ) on Sunday March 14, 2004 @03:50PM (#8562847) Homepage Journal

          Quoth grandparent: Pluto should be labeled an asteroid since it's smaller than even our own moon.

          Quoth parent: Frankly, I don't understand this line of reasoning. Why does it matter, with regards to whether something is a "planet" or not, whether that thing is bigger than, for example, our moon?

          I agree with parent that in this case size really doesn't matter: it's all in how you use what you got.

          Historically, Neptune was discovered because it was perturbing Uranus' orbit: its existence was theorized long before it was directly observed. Similarly, Pluto was discovered because it was found that Neptune alone was not sufficient to account for all of Uranus' irregularity. While Pluto isn't very big, its size and orbit are such that it definitely affects the other planets.

          In practice then, what we have actually used to distinguish a planet like Pluto from a large body that is not a planet, like Chiron (roughly as big, discovered 1977), is whether the object interacts in a measurable way with known planets. If it does, then accord it planet status because it is clearly part of the planetary system.

          In view of this, the new discovery is probably not a planet, unless it has a weird orbit like Pluto and would account for some of the remaining difference between planetary observations and expectations.

          But what do I know? IANAA.

        • by CrazyTalk ( 662055 ) on Sunday March 14, 2004 @04:06PM (#8562923)
          I remember hearing awhile back when the debate was raging about Pluto that to be a planet, the object has to be sufficently large so that gravitational forces caused it to form in the shape of a sphere. So, varous small hunks of debris orbiting the sun definately are not "Planets". At the other end of the spectrum, objects large enough to radiate a certain amount of heat are considered stars. Neither of these definitions are exact, and the astronomy dictionary will probably need to be rewritten with all the recent scientific discoveries emerging, but there are some definitions out there that are not completely arbitrary.
      • by r2vf ( 761602 ) on Sunday March 14, 2004 @02:47PM (#8562492)

        IMO, Pluto should [shouldn't?] be labeled an asteroid since it's smaller than even our own moon [].

        An interesting point, though to be fair, its an arbitrary cutoff. There are moons elswhere in our solar system larger than Mercury, which is indisputably a planet, for example. Also its worth pointing out that our moon is large enough that it and Earth are sometimes called a double planet. Consider this, Luna does not orbit Earth as near the equator as is usual among most other moons. Also, peculiar to all 138 known moons with the exception of Charon, it possesses an orbit where the effect of the Sun's gravity is greater than that of Earth's. Without their host planets, they would float off, wheareas the moon would continue orbiting the sun quite contently.
        • by el-spectre ( 668104 ) on Sunday March 14, 2004 @03:46PM (#8562807) Journal
          To be fair, luna is also the closest moon to the sun by a hundred million miles...
        • Escape velocity (Score:5, Informative)

          by geoswan ( 316494 ) on Sunday March 14, 2004 @04:06PM (#8562926) Journal
          Without their host planets, they would float off, wheareas the moon would continue orbiting the sun quite contently.

          I have been interested in Astronomy since I was about six years old. Just over forty years. I have heard what you suggest before -- but only in the last few years. And I don't understand it any more this time than I did on the earlier occasions.

          Frankly, I strongly suspect it is a false factoid, like that the internet was built to survive a Nuclear War. I strongly suspect it is a bullshit meme that keep being repeated because it sounds cool, but is completely false.

          Pray explain what you mean when you say the other 138 moons would float off ?

          I am trying to do the "thought experiment" of silently, quietly erasing the principals of those moons, mass and all. I am finding this difficult to do. I don't believe there is any way this could occur, in our Universe.

          So, instead I imagined doing something to accelerate a moon, any moon, to the escape velocity of its principal. What happens then? Well, the object accelerated to just beyond a planet's escape velocity will assume an orbit very similar to that of the Planet it just escaped from. Sometime in the last couple of years ago there was a flap about a small object [] that seemed to have been temporarily captured in the Earth-Moon system. But it turned out to be NASA space debris. It appeared to be the discarded upper stage of an Apollo moon shot.

          • Re:Escape velocity (Score:4, Informative)

            by Doomdark ( 136619 ) on Monday March 15, 2004 @01:02AM (#8565848) Homepage Journal
            false factoid, like that the internet was built to survive a Nuclear War.

            Perhaps it's a typo from your part -- original Arpanet was certainly designed such that a network could be built that would survive effects of parts of network to be completed wiped out; something that could happen as a result of nuclear strike. I don't think Arpanet infrastructure itself was more than a (eventually large-scale) prototype (physically, I mean; protocols were certainly engineered correctly), and thus neither it, nor Internet later on, was built to be as tolerant as what protocols would allow.

            That Arpanet was designed to survive catastrohic (yet not completely destructive -- there still has to be at least one route between nodes that want to communicate, obviously), is not an urban legend , and should be easily verified from various accounts by its creators.

        • by MickLinux ( 579158 ) on Sunday March 14, 2004 @04:47PM (#8563156) Journal
          The moon's orbit is everywhere concave towards the Sun. Therefore, the moon is a satellite of the Sun, and not a satellite of the earth. As such, perhaps it should be called a member of a binary planetary system.
      • by catbutt ( 469582 ) on Sunday March 14, 2004 @03:27PM (#8562697)
        So where's the line between asteroid and planet?

        Why does there have to be one? Man's tendency is to compartmentalize things, to make sure everything has a name and that name is unambiguous. Problem is, nature doesn't cooperate. There are always going to be intermediate forms, so there are never going to be definitions that aren't arbitrary.

        Same thing applies to species. The nice simple definition "if it can interbreed, its the same species" doesn't always work, and there is no reasonable definition that covers all cases and removes ambiguity.
      • by geoswan ( 316494 ) on Sunday March 14, 2004 @03:32PM (#8562714) Journal
        Is this a decision based on Science? Or is it based on Politics and emotion?

        Did you know that in 1998 Senator Patrick Leahy, of Vermont, got his State's largest Lake, Lake Champlain, to be reclassified as the 6th Great Lake? [] At least as far as the awarding of researh grants. Being considered a "Great Lake" made the academic institutions in his constituency eligible to apply for certain research grants.

        There is talk of sending a probe to Pluto. Is it possible that it is easier to sell a probe to "planet Pluto" than to send one to Kuiper-belt object Pluto?

        I remember, back in the days when I tuned in to debates as to which newsgroups should be created, the big debate as to whether a new group should be talk.acquaria, rec.acquaria or sci.acquaria.

        In Leahy's defence, these were environmental research grants, and I should probably assume he added this line to the bill to protect his constituent's natural environment -- not for the petty partisan purposes.

    • by Rick the Red ( 307103 ) <Rick DOT The DOT Red AT gmail DOT com> on Sunday March 14, 2004 @02:21PM (#8562321) Journal
      What we need is a simple rule: If it orbits a star and has an atmosphere, it's a planet. If not, it's not. I.e., things orbiting other planets are moons, even if they have an atmosphere. Things orbiting a star are asteroids (or whatever) if they don't have an atmosphere, no matter how large they are.

      Pluto has an atmosphere [], so it's a planet. What about Sedna? Does anyone know, or must we wait until Monday?

    • by big_groo ( 237634 ) <(moc.liamg) (ta) (sivoorg)> on Sunday March 14, 2004 @02:31PM (#8562381) Homepage

      Here----> .

  • by Operating Thetan ( 754308 ) on Sunday March 14, 2004 @01:27PM (#8561921) Journal
    Cue conspiracy theories, New Age freaks, Planet X believers and other idiots. Still, at least this discovery has the redeeming quality of completely fucking up astrology
  • by dealsites ( 746817 ) on Sunday March 14, 2004 @01:28PM (#8561926) Homepage
    I wonder what is so important that NASA is going to wait until Monday. Maybe they will be unveiling something else at the same time?

    Real-time deal updates []
    • by AnamanFan ( 314677 ) <anamanfan&everythingafter,net> on Sunday March 14, 2004 @01:35PM (#8561993) Homepage
      It's a standard rule of Public Relations. Never announce anything between Friday at 4pm till Monday at 8am.

      The reason being that news outlets are not at full capacity during the weekends, so any news announced over the weekend won't get as much coverage. If NASA announced the news today, it will be covered on the Sunday evening news, and never again since that piece of news was already done, even when not many saw it.

      You can notice this practice when someone famous dies over a weekend. There will be an immediate announcement saying that the person is missing or very ill or something of the sort, then make the announcement on Monday.
      • by Bearpaw ( 13080 ) on Sunday March 14, 2004 @02:22PM (#8562329)
        It's a standard rule of Public Relations. Never announce anything between Friday at 4pm till Monday at 8am.

        Unless, of course, it's something you have to announce for some reason but don't want most people to hear. Then late Friday afternoon is the perfect time to announce it. Politicians do this a lot. It would probably be quite instructive to review Friday late-afternoon press releases from the White House, for the last two or three decades.

    • by gnu-generation-one ( 717590 ) on Sunday March 14, 2004 @02:21PM (#8562324) Homepage
      "I wonder what is so important that NASA is going to wait until Monday. Maybe they will be unveiling something else at the same time?"

      It's the monthly bug-report announcement. "A local root vulnerability has been found in the astrology community. NASA rates it as non-critical"
  • whew! (Score:5, Funny)

    by odano ( 735445 ) on Sunday March 14, 2004 @01:28PM (#8561929)
    Thank god I am out of elementary school. Memorizing 9 planets was hard enough, but 10! They have got to be kidding.
  • by LostCluster ( 625375 ) * on Sunday March 14, 2004 @01:29PM (#8561934)
    The order of planets we all learned in 4th grade was out of date already because now Neptune is further away than Pluto. Now, I guess we're going to have to memorize another planent for the next quiz.
  • Alf (Score:3, Funny)

    by TheGreatAvatar ( 49772 ) on Sunday March 14, 2004 @01:29PM (#8561936) Homepage
    was right after all!

  • by Anonymous Coward on Sunday March 14, 2004 @01:30PM (#8561943)
    Pluto is 2300 km diameter, ranges from 4.3 to 7.4 billion km from the sun. stics.html []
  • by meringuoid ( 568297 ) on Sunday March 14, 2004 @01:30PM (#8561949)
    ... and the last I heard was that it was about the size of Charon. I doubt it will ever be recognised as a planet - we already have Quaoar out there and swarms of other little Plutinos.

    Whether Pluto is 'really' a planet or just a big Kuiper object seems to be a silly argument. Even if it's not justifiable, we'll call Pluto a planet out of tradition.

    • by Gutboy_Barrelhouse ( 260624 ) on Sunday March 14, 2004 @01:57PM (#8562179)
      No. Charon is slightly smaller than Quaoar.

      Sedna is over 4 times the size (volume) of Quaoar.

      Whether it's a planet is a silly argument, but even so, "we already have Quaoar" is really irrelevant.

    • by AlecC ( 512609 ) <> on Sunday March 14, 2004 @02:30PM (#8562376)
      The concept of Planets should no longer be regarded as a formal (as opposed to colloquial) classification. We have four rocky inners, four gassy outers, and a vast number of planetismals. Forming a group of the first two classes, with or without a few of the last, is a false classification.
    • by RobertFisher ( 21116 ) on Sunday March 14, 2004 @02:53PM (#8562525) Homepage Journal
      The question becomes even more convolved once we move outside the solar system, since we now know of a wide diversity of systems, of which our own solar system is only one particular instance. (And perhaps not even typical at that.) We know that there are objects extending all the way down from massive stars (around 100 Msun) to hydrogen-burning stars like our sun to brown dwarfs to planets. Clearly any definition of a planet must apply not only to our solar system, but also to these extrasolar systems. Some of these systems are much like our own (for instance, they may contain a brown dwarf orbiting a star, or a planet orbiting a star), and some (including a few systems of low enough mass to qualify as a planet) are "free-floaters" -- just sitting out there by themselves in space.

      I think ultimately the question is whether there is a single continuous "initial mass function" of isolated objects or not. The best idea as to how stars acquire their initial mass is that turbulence in the interstellar medium, which exists on all scales, establishes a power-law distribution of initial masses. Every once in a while, you get a very strong shock which passes by inside a giant molecular cloud and forces the collapse of a large region which then goes on to form a massive star. But more typically, you form stars more like our sun. And just as rare as massive collapses are very small mass ones which go on to form isolated brown dwarfs and free-floating planets. If this model holds up to be true, then we are all mincing words in our definitions of isolated systems, since they are all manifestations of the same universal formation process.

      However, to avoid the difficult question of formation mechanisms, an IAU working group of some of the most respected people in the field established a working definition [] to define by fiat what it means to be a brown dwarf, and a planet. Extrasolar "planets" are those objects orbiting a star which are beneath the deteurium-burning limit -- regardless of how they are formed. "Brown dwarfs" are defined to be those which burn deuterium but not lithium, and "sub-brown dwarfs" (NOT free-floating planets!) are defined to be those isolated objects which do not burn deuterium. Even the working group itself admitted that this definition was not satisfying to a single member of the group, and so it is likely it will be replaced at a later time with something more physically-motivated. The "planet/planetismal/KBO" distinction was pushed back to our own solar system, since it will be some time before anyone sees anything that small in another system.

      Also of interest is the following link, which gives a history of previous claims for additional planetary members of our solar system : SEDS [].

  • I thought planets were Roman gods. It's not even like we've run out of them. We can still find Vulcan (Mulciber if you want to avoid rabit Trekkies), Juno, Minerva, Apollo (You can call this one Phoebus if you want to avoid confusing it with space probes), Diana, Vesta.

    And that's before you start getting slightly obscure ones like Janus, Bacchus (Or Liber), Fanus, Quirinus, Pomona, or Vertumnus.
  • I claim it (Score:3, Funny)

    by AbstracTus ( 576474 ) <einar AT binary DOT is> on Sunday March 14, 2004 @01:32PM (#8561970) Homepage
    Please email resident applications to me.
  • They (Score:4, Funny)

    by chadseld ( 761331 ) on Sunday March 14, 2004 @01:33PM (#8561977)
    They should call it rupert.
  • by mbone ( 558574 ) on Sunday March 14, 2004 @01:33PM (#8561982)
    Out in the Kuiper belt and the Oort cloud [] there are thought to be as many as one trillion objects - most small 1 to 10 km chucks of ice.

    The really interesting question is, what is the mass distribution ? (I.e., how does the number of objects scale with their mass ?) This is basically unconstrained by real data. All such cosmic mass distributions are steep, but many (for example, planets in the Solar System, Asteroids in the Asteroid belt) are dominated by the most massive bodies.

    If this holds true in the Oort cloud, in particular, there could be some pretty big objects. Even a Jupiter sized object might be able to hide from the Infrared surveys (the best way of detecting such an object).
    • by mikerich ( 120257 ) on Sunday March 14, 2004 @02:43PM (#8562457)
      If this holds true in the Oort cloud, in particular, there could be some pretty big objects. Even a Jupiter sized object might be able to hide from the Infrared surveys (the best way of detecting such an object).

      Clyde Tombaugh who discovered Pluto performed an exhaustive search for Planet X for several decades. From his results he concluded that there were no undiscovered Jupiter-sized bodies within 470AU of the Sun, and no Neptune-sized objects with 210AU. (Pluto is never more than 50AU from the Sun).

      The Oort Cloud is believed to have been populated by planetismals thrown out of the early inner part of the Solar System by the formation of Uranus and Neptune. They would have slungshot smaller bodies into the outer darkness into orbits that match the hypothetical orbits in the Oort Cloud. They would not have been able to shunt anything larger out that far - at least not without disrupting their own formation.

      A further problem is that planet formation models run into trouble this far out. Distances between the planetismals that made up the proto-planets would have been so great, and relative velocities so small that its hard to see how they would ever have collided to built up a bigger planet.

      Best wishes,

  • by sudog ( 101964 ) on Sunday March 14, 2004 @01:38PM (#8562028) Homepage
    I for one welcome our new Mi-Go masters!
  • by schnarff ( 557058 ) <> on Sunday March 14, 2004 @01:42PM (#8562064) Homepage Journal
    I think I can answer all of the people on here who are asking "Why didn't they go with a Roman name?". It's real simple: political correctness. After all, Roman names were given to the planets by a bunch of old, dead white men, and are a vestige of a conquering, warfaring civilization. This new Inuit name represents one of those poor, marginalized, powerless indigenous tribe types. It's like affirmative action for planets.

    Personally I think we should have just stuck with the Roman names and kept a consistent system...but then again, I am a middle-class white male. ;-P
  • by SmallFurryCreature ( 593017 ) on Sunday March 14, 2004 @01:46PM (#8562097) Journal
    Screws up astrology and that can only be a good thing. Lets add one every 2-3 years and watch them squirm.

    Anyway something 2000km in diameter is hardly small. Aren't astoroids that could kill earth just a couple of kilometers accross?

    Anyway excluding it is sizeist. Can't have that. If you are going to classify keep it simple. Object larger then a rock orbetting the sun and being close to round. I think that is what most people consider a planet.

    So welcome sedna.

    • Hrmm, I agree screwing up astrology is always a good thing. But what if this HELPS them? What if now astrologers defend all their false "predictions" by explaining that it was in fact Sedna's influence that skewed the results?


  • Not a problem yet (Score:5, Interesting)

    by SiliconEntity ( 448450 ) on Sunday March 14, 2004 @01:47PM (#8562104)
    It won't be an issue until they find a Kuiper object that is bigger than Pluto. Then they'll have an awkward situation. Making Pluto a planet when this bigger object isn't one doesn't make sense; nobody wants to add a new planet, because in retrospect it was a mistake to make Pluto a planet, and adding another Kuiper object would just compound it; and removing Pluto from the list of planets offends tradition.

    Everyone wants to push this off as long as possible, so if the new object is really smaller than Pluto, they'll breathe a sigh of relief and go on with things as they are.
  • That would be 11th! (Score:3, Informative)

    by Vo0k ( 760020 ) on Sunday March 14, 2004 @01:54PM (#8562160) Journal
    Quaoar [] (though some claim it's too small for a planet...)

    Alf predicted them both!
  • If I remember (Score:4, Interesting)

    by bigattichouse ( 527527 ) on Sunday March 14, 2004 @02:08PM (#8562243) Homepage
    There was a formula for predicting orbital paths that was related to Fibbunaci's sequence, I wonder if sedna falls into the sequence?
  • by pla ( 258480 ) on Sunday March 14, 2004 @02:15PM (#8562287) Journal
    Sedna? No. Plenty of people in this thread have complained about two facts - One, our planets have names derived from the Roman, not Inuit, panthon. And two, we already have a planet named after a sea-god, ie, Neptune.

    So, I propose that in protest to such a blatant attempt at PC Multiculturalism, we as a community refer to the tenth planet as Nox, the Roman goddess of night. Since it lies the furthest from the sun, that actually fits it, in a descriptive sense.

    Sedna... Whatever. Remember, we hear about this stuff months before your typical Fox news junkie, and people tend to respect us as sources of information. So spread the word - We have a new, tenth planet, named Nox. Sedna? Nope, they must have heard wrong. Nox. Nox? Nox!
  • by bpd1069 ( 57573 ) on Sunday March 14, 2004 @02:15PM (#8562288) Homepage
    for obvious reasons...
  • by joebeone ( 620917 ) on Sunday March 14, 2004 @02:18PM (#8562302) Homepage

    My former advisor here at UC Berkeley, Gibor Basri, has a neat way of discriminating between planets and the lesser (comets, asteroids, etc.). His idea is that if the object has enough self-gravity to force it into a spherical shape, it's a planet... if it doesn't (like Mars' "moons"), it's something less.

    Here's a snipet:

    How can this be resolved? A consensus is slowly developing (I believe) for the following solution. We can first define what we mean by "planetary mass", and base this only on physical characteristics. Then we can include circumstance into the definition of "planet". I propose the following three definitions:

    FUSOR - an object that achieves core fusion during its lifetime.

    PLANEMO - a round non-fusor.

    PLANET - a planemo orbiting a fusor.


    read on for his full article [].

    The following is a draft of an article now published in the Nov/Dec 2003 issue of Mercury. Draft of Mar. 20, 2003.

    Defining "Planet" by Gibor Basri Univ. of California, Berkeley

    Even before they were civilized, people looked into the sky and recognized different celestial objects. The Sun defined daytime, and the stars provided a fixed background of faint, twinkling lights at night. Among them moved the Moon, and a few special steadier lights. The Greeks called those which moved "planets" (it is worth noting that the Sun and Moon were originally included, since motion against the stars was the defining characteristic). Most cultures have an analogous word for these "wanderers". Both the stars and the planets were thought to revolve around the Earth.

    After the Copernican Revolution, we recognize the Moon as the only body that orbits the Earth. The Sun is a very nearby example of a star, and the visible planets are other large bodies that orbit the Sun. We see them by reflected sunlight, while stars produce their own visible light. This understanding yields the dictionary (lay public) definition of the word "planet": a large heavenly body that shines by reflected light and orbits the Sun. In the past century we gained much understanding of our Solar System, and even visited most of the planets robotically. Yet today, professional astronomers find themselves unable to agree upon a succinct definition of "planet". Replacing "the Sun" with "a star" is obviously necessary now that many extrasolar planets have been discovered, but the problem goes well beyond that.

    Two recent controversies that found their way to the popular press illustrate further difficulties. One is the "Pluto controversy". This arose because of the discovery of a large belt of icy objects beyond Neptune. They are the outer remains of the original protoplanetary disk. This "Kuiper Belt" is a natural outcome of incomplete planet formation in the outer Solar System, and is the source of some of the comets we see. As Kuiper Belt objects (KBOs) were discovered in increasing numbers in the 1990s, including a population of "Plutinos" which share Pluto's orbital characteristics (somewhat different from the other planets), some astronomers began to suggest that Pluto itself (which shares many properties with, but is the largest KBO known so far) does not qualify as a planet. The recent discoveries of Varuna and Quaoar (which are KBOs half the size of Pluto, like its moon Charon) may presage the time when we find another Pluto-sized KBO.

    The current situation is much like that in the early 1800s, when the first asteroids were discovered. Ceres was originally hailed as the fifth planet, particularly since one in its position was expected from "Bode's Law" of planetary spacings. It lost its status within a few years, when other members of the asteroid belt began turning up. Herschel, who had been the only person to have discovered a new planet before then, aided the effort to demote Ceres. The arguments against its planeta

  • by Boss, Pointy Haired ( 537010 ) on Sunday March 14, 2004 @02:49PM (#8562503)
    This will be handy for those short-sighted sysadmin types that name their servers after finite sets like planets.

    Now they'll be able to buy up to 10 servers before re-thinking their naming strategy.

On the Internet, nobody knows you're a dog. -- Cartoon caption