2003 Ub 313: The Incredible Shrinking Planet?, No bigger than Pluto? |
2003 Ub 313: The Incredible Shrinking Planet?, No bigger than Pluto? |
Guest_BruceMoomaw_* |
Jan 31 2006, 09:20 PM
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Guest_BruceMoomaw_* |
Apr 12 2006, 12:09 AM
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Robert Roy Britt, in his blog on this subject ( http://www.livescience.com/blogs/author/robbritt ), positively DEMANDS that both Pluto and 2003 UB 313 not be called "planets" yet, unless the IAU gives us permission to do so. Who died and made YOU King of the Solar System, Robert?
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Apr 12 2006, 03:37 AM
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Member Group: Members Posts: 307 Joined: 16-March 05 Member No.: 198 |
Robert Roy Britt, in his blog on this subject ( http://www.livescience.com/blogs/author/robbritt ), positively DEMANDS that both Pluto and 2003 UB 313 not be called "planets" yet, unless the IAU gives us permission to do so. Who died and made YOU King of the Solar System, Robert? Well, to be fair he is trying to make a legitimate point: "Objects like Pluto and 2003 UB313 should be called minor planets or dwarf planets or something else that denotes their relative insignificance compared to the four inner terrestrial planets and the four outer giants. And therein lies the precedent: We already have terrestrials and giants. Just add dwarfs." That sounds like the very solution astronomers used to resolve the pesky problem of Ceres and the asteroids (aka "minor planets") back in the 1800s. Unfortunately, given we already do have a class of astronomical bodies dubbed "minor planets" you have wonder whether it would be wise to either extend that name to Kuiper Belt objects or invent a special term ("dwarf planets") for KB objects that could well end up be confused for the other one. In particular, I notice astronomers themselves seem to be at pains to avoid using the word "asteroid" for KB objects. Yet if they did start using "minor planet" as a label for such objects, or a name which could well be confused with it (eg "dwarf planets"), then the existing association in many people's minds between "minor planets" and "asteroids" may well eventually lead to the "asteroid" label being applied to KB objects also, even if only by lay folk. *** One further point on the more general issue of "is it/is it not a planet?" The whole debate seems to depend not on the nature of the object but on its size. Yet in a sense it is not just size that seems to matter either. It is arguably as much about numbers. So long as there was only one body in the asteroid belt or out in the Kuiper Belt nobody--including astronomers--seemed to much mind calling both "planets". It was only when asteroids and Kuiper Belt objects started to proliferate like rabbits that astronomers started getting cold feet about the term. Yet curiously this need to distinguish Pluto and Ceres from planets does not apply to two other general terms: stars and moons. There are red supergiants out there and there are red dwarfs, but at the end of the day they are all termed "stars". (Only with "brown dwarf" does there seems to be a reluctance to use the word; and then it's arguably because of their nature: brown dwarfs are seen as failed stars.) So too with "moon". While we sometimes hear the term "moonlet" bandied about, nobody seems to be (yet) suggesting we reserve that prestigious term "moon" for the larger objects circling planets and use some other label ("minor moons"? "dwarf moons"? "lunar objects"? "orbital rubble"?) for the riff-raff. (Although maybe astronomers are holding fire on that debate until Cassini or some successor probe actually images a few of the house-size "moons" in Saturn's rings.) That raises the question of whether this present "is it/is it not a planet" debate--as well as the one back in the 1800s--doesn't involve more than modicum of--er--snobbery. Or to phrase the issue another way, I cannot help feeling the only reason this debate has arisen at all with "planet" is because Earth just so happens to bear the label "planet"; and despite all that has come and gone there is still a subconscious wish, even amongst some astronomers, for Earth to be part of a group with a certain degree of--shall we say--exclusivity. Meaning that if Earth had been a moon rather than a planet would we now be arguing over whether to admit Janus to the hallowed ranks whilst not giving two hoots about using "planet" for Pluto and Ceres? Thus, it is all right for Jupiter to be called a "planet". That then puts Earth among the giants. We are even prepared to tolerate midgets like Ceres and Pluto being one--so long as there was only just one of each. Once there start to be too many of such small fry the feeling seems to be that the term "planet" is losing its currency. Hence, while nobody seems to mind labelling Janus or Miranda "moons" were they orbiting the Sun rather than Saturn & Uranus nobody would be calling them "planets". Similarly with Pluto or (say) Ida. Were Pluto or Ida in orbit around a planet astronomers would be quite happy to label both of them "moons". Only when they start circling the Sun does size suddenly become an issue. ====== Stephen |
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