2003 Ub 313: The Incredible Shrinking Planet?, No bigger than Pluto? |
2003 Ub 313: The Incredible Shrinking Planet?, No bigger than Pluto? |
Apr 12 2006, 03:37 AM
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#46
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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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Apr 12 2006, 03:41 AM
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#47
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Merciless Robot Group: Admin Posts: 8784 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
The IAU & everyone else has to face up to one fundamental fact: the objects in the Solar System exist along a continuum of sizes, from individual hydrogen atoms to Jupiter. Defining what is and is not a planet will always be a purely arbitrary convention by any objective standard, except for the apparent distinction that a planet has to independently orbit the Sun. Maybe it's time to throw out the concept entirely...?
Well, short of that heresy, maybe we just need to distinguish between "major" and "minor" planets. If that definition were adopted, I'd say that Mercury becomes the standard minimum body, and we have eight major planets. (Let's face it: it's embarrassing that Pluto is only half the size of the Moon!) -------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Apr 12 2006, 04:45 AM
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#48
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Member Group: Members Posts: 307 Joined: 16-March 05 Member No.: 198 |
Well, short of that heresy, maybe we just need to distinguish between "major" and "minor" planets. If that definition were adopted, I'd say that Mercury becomes the standard minimum body, and we have eight major planets. (Let's face it: it's embarrassing that Pluto is only half the size of the Moon!) The problem is that it's easy to say that now with just one solar system and nine (or eight or ten, depending on who's counting) planets. What happens when we start finding solar systems where the equivalent of Mercury is the size of Europa or Triton? Is the response of astronomers to be: Sorry, you have to be "this big" to qualify as a planet. ====== Stephen |
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Guest_BruceMoomaw_* |
Apr 12 2006, 04:51 AM
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#49
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Guests |
I remain convinced of what I said in 1999: if you are going to call some things "planets" at all, it must be on the basis of their being above some size -- and since that size is ultimately entirely arbitrary, let's set it at some figure that (just barely) lets Pluto retain its historical status that everyone's used to, while not letting a lot of smaller riffraff join the club. 2000 km seems the perfect figure for this purpose. Then -- for the sake of everyone's sanity -- let's DROP THE SUBJECT.
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Apr 12 2006, 05:15 AM
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#50
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Junior Member Group: Members Posts: 37 Joined: 21-December 05 Member No.: 614 |
QUOTE The problem is that it's easy to say that now with just one solar system and nine (or eight or ten, depending on who's counting) planets. What happens when we start finding solar systems where the equivalent of Mercury is the size of Europa or Triton? Is the response of astronomers to be: Sorry, you have to be "this big" to qualify as a planet. For some reason the exoplanets in the PSR 1257+12 system never get a lot of attention, yet they are as small or even smaller as Pluto. Did we discover small planets or are they the first asteroids/minor planets we found around another star? |
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Apr 12 2006, 05:45 AM
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#51
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Member Group: Members Posts: 249 Joined: 11-June 05 From: Finland (62°14′N 25°44′E) Member No.: 408 |
PSR 1257+12 B and C are a few times more massive than the Earth, A is about the size of the Moon. There's probably yet another body, but not even the discoverers call it a planet as it is has only one fifth the mass of Pluto.
-------------------- The universe is not only stranger than we imagine, it is stranger than we can imagine.
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Apr 12 2006, 06:05 AM
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#52
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Member Group: Members Posts: 307 Joined: 16-March 05 Member No.: 198 |
PSR 1257+12 B and C are a few times more massive than the Earth, A is about the size of the Moon. There's probably yet another body, but not even the discoverers call it a planet as it is has only one fifth the mass of Pluto. Interesting. Yet again it seems to be only the term "planet" which attracts this debate. Consider neutron stars. They are not even as big as many asteroids or Kuiper belt objects, much less Pluto, yet no astronomer seems to be suggesting that their diminutive size means we should stop calling them "neutron stars" and dub them (say) "neutron objects" or "neutron dwarfs" instead. ====== Stephen |
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Apr 12 2006, 08:16 AM
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#53
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Member Group: Members Posts: 249 Joined: 11-June 05 From: Finland (62°14′N 25°44′E) Member No.: 408 |
It's the mass that dominates. Even the least massive neutron stars are more massive than the Sun, and the upper limit of neutron stars is somewhere three times solar mass. So calling them "dwarfs" would be misleading despite their tiny size. But of course calling them stars is also wrong because they are not real stars anymore.
-------------------- The universe is not only stranger than we imagine, it is stranger than we can imagine.
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Apr 12 2006, 08:28 AM
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#54
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Member Group: Members Posts: 809 Joined: 11-March 04 Member No.: 56 |
The IAU & everyone else has to face up to one fundamental fact: the objects in the Solar System exist along a continuum of sizes, from individual hydrogen atoms to Jupiter. Defining what is and is not a planet will always be a purely arbitrary convention by any objective standard, except for the apparent distinction that a planet has to independently orbit the Sun. Maybe it's time to throw out the concept entirely...? Well, short of that heresy, maybe we just need to distinguish between "major" and "minor" planets. If that definition were adopted, I'd say that Mercury becomes the standard minimum body, and we have eight major planets. (Let's face it: it's embarrassing that Pluto is only half the size of the Moon!) Earth people are known for their curious definitions, but this one is quite astounding; every schoolchild knows that planets, other than the minor planets, have an atmospheric depth of at least 5000 km, are massive enough to attract a large system of satellites, and have rings. Some silly proposals have been made to include the rocky, almost atmosphere-less inner bodies as "planets", but they have perished from their self-evident absurdity. After all, our schoolchildren have only four tentacles; why should we expect them to memorize more than four planets? Jupiter, Saturn, Uranus, and our own beloved Neptune: it was good enough for Zaljyx, and it's good enough for me! |
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Apr 12 2006, 09:31 AM
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#55
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Senior Member Group: Members Posts: 1870 Joined: 20-February 05 Member No.: 174 |
....it was good enough for Zaljyx, and it's good enough for me!
If you think these verses floor us Then go write another chorus Just as long as you don't bore us Then it's good enough for me! http://www.whitetreeaz.com/vintage/realotr.htm For 880 verses to "REAL OLD TIME Religion" and enough not yet entered to put the count over 1000. (Yes... they've got verses to offend everybody who isn't laughing so hard their glasses fog up) |
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Apr 12 2006, 01:24 PM
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#56
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Senior Member Group: Members Posts: 1276 Joined: 25-November 04 Member No.: 114 |
Here is a image comparison... http://www.nasa.gov/images/content/146570main_xena_size.jpg
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Guest_JamesFox_* |
Apr 12 2006, 01:37 PM
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#57
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Guests |
When I read that blog by Robert Roy Britt, I noticed the he acts as if it's a proven scientific fact that Pluto and 2003 UB313 are not planets, but the only reason he gives is that the 8 other planets have low inclination, as opposed to high ones. He also ignores (like most others), the fact that the term minor planet is already in use.
Many of those objecting to Pluto's status also seem to act as if the whole purpose of defining a planet is to provide a list for schoolchildren. In doing so, they tend to automatically ignore extrasolar planets - some even go so far as to declare that planets must orbit our sun (or even worse, insist that they must orbit at Neptune's distance or closer!) . They then compile lists of attributes that separate Xena and Pluto from the other 8, and use them to make anti-Kuiper belt planet definitions. The inclination argument is one I've seen before. For example, I remember seeing a nice chart of inclination versus mass that seems to boost the anti-pluto case. However, a number of large extrasolar planets have very high eccentricities, even crossing the orbits of other planets in thier systems. Although their inclinations are unknown, it seems likely that some of them have high inclinations. In addition, would there be some sort of rule against having Pluto in a Quaoar-like orbit? Perhaps something like this exists in some extrasolar system. I suspect that many people simply don't like Pluto or Xena, and feel that they are too small and wierd to be included alonside Mars or the Earth. So definitions are invented to exclude them, in an attempt to pretend that they are not being arbitary. Ignoring extrasolar planets makes this easier. When you look at these definitions more closely, however, hard boundaries and classifications are revealed as just as arbitrary as a lower size limit. In the end, planets are largeish, round, and do not orbit planets seems to be the only general (if vague) definition in common use, before people started to try to kick Pluto out of the club. Since there is, in my opinion, no accepted scientific definition, a formal planet definiton should take the previous into account. Also, we have to deal with the minor planet issue. |
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Apr 12 2006, 01:46 PM
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#58
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Member Group: Members Posts: 593 Joined: 20-April 05 Member No.: 279 |
Defining what is and is not a planet will always be a purely arbitrary convention by any objective standard, except for the apparent distinction that a planet has to independently orbit the Sun. Independently? Well, that rules out the Earth-Moon binary system then. ;-) Andy |
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Apr 12 2006, 02:01 PM
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#59
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Member Group: Members Posts: 159 Joined: 4-March 06 Member No.: 694 |
...as Triton did. As child I read in an old astronomy library book from the '50s - I think it was from Otto Struve - Triton's diameter should be ~6000 km: 'Wow, a moon nearly as large as Mars...' I'm not quite sure what it was before Voyager II - maybe about 3500 km, but at the the end it came down to poorly 2720 km, probably the same size as UB313 now. If we get more cases like Pluto, Triton, UB313, we'll find a 'shrinking law' from 'detection-diameter' to real diameter at the end... Bye. I do remember that someone used the "speckle infrarometry" method to measure Triton's diameter before the Voyager 2 flyby. They got a figure of 2,500 km. Could they use this method on UB313? -------------------- I call heaven and earth to witness against you this day, that I have set before thee life and death, the blessing and the curse; therefore choose life, that thou mayest live, thou and thy seed.
- Opening line from episode 13 of "Cosmos" |
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Apr 12 2006, 04:48 PM
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#60
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Junior Member Group: Members Posts: 34 Joined: 9-January 06 Member No.: 639 |
I do remember that someone used the "speckle infrarometry" method to measure Triton's diameter before the Voyager 2 flyby. They got a figure of 2,500 km. Could they use this method on UB313? Right now, I wouldn't be surprised to see 2003 UB313 end up being smaller than Pluto. Later! J P |
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