Definition of "planet"

[cookie_thief]

I like the term <i>Kuiper Belt Planet</i>. It describes the object as a member of a sub-class of planets that reside within the reaches of the Kuiper Belt. It puts in place a classification process for others objects that remain to be discovered as well. It's as good a compromise as any I've seen and I think it would be culturally acceptable. <br /><br />I'm not sure how the scientists would feel about it, but all they would have to do is is to iron out the difference between KBOs and KBPs.

 

[vidar]

I think that KBO and KBP (or even KB Moon) could be temporary terms until we know more. I think most star systems have made belt and clouds at 50 AU and beyond. <br /><br />But I also think the KB definitions will not help us much when mapping other solar systems. Still the planets should be defined by their properties and not their positions.<br />

 

[Philotas]

I mean that there (for our solar system only) should be two major groups of planets: the major planets and the smaller/lesser planets. I bring this up only to make it easier for the public to know what`s the biggest and most 'important' planets in our system, and for those who are critical to the definition because of the high number of planets we will end up with. <br />Once outside our system we don`t need these two classifications anymore, and only divide planets into classes like gas giants, terrestrials etc.<br /><br />It`s not difficult to deal with the Centauri system all; just change the definition from "object oriting a star" to "object orbiting one or more stars", or alternatively "a round object composed of normal matter; not a blackhole or any other exotic object, and does not exceed 13X the size of Jupiter"(this means that a planet doesn`t have to orbit a star at all). Any object zig-zagging must still somehow orbit the stars, otherwise it wouldn`t be in the system.<br /><br />The dwarf star is still a star despite orbiting any of the other stars in the system, so any round object orbiting Proxima Centauri(believe that`s it name) would be a planet.<br /> Any object orbiting a planet in the Centauri system would simply be a moon. <div class="Discussion_UserSignature"> </div>

 

[jroswald2001]

Once upon a time we had four elements, now we have more than 130. We have now discovered many new planets beyond our own solar system, and this will demand a fundametal rethink as to how we classify them.<br /><br />First up, calssifications should be based primarily on physical parameters, and not whether a body is orbiting a sun or not. Where bodies orbit a star, they should be called "primary planets", and where they order a "primary planet" they should be called a secondary planet. Objects should only be called primary or secondarry planets if they fulfill one basic criteria, they should be large enough for their gravity to form themselves into a sphere or elliptoid (e.g. Saturn). Just what is the point of all these discoveries of new satellites of Saturn that are hardly large enough to punch a hole in a bag full of Kelloggs corn flakes....i exaggerate, but surely you get the point. <br /><br />The physical classification of planets should be carried out in exactly the same way for both primary and secondary (or indeed tertiary etc.) planets. We can have gas giants, terrestrial rocky worlds, ice giants that be either secondary or primary in nature. As subdivisions of terrestrial worlds, we could add the definition as to whether these worlds are of an icy or rocky composition (in the jovian system there could be hybrid possibilities). <br /><br />So in our solar system we have <br /><br />gas giants (2): both primary<br />ice giants (2): both primary<br />rocky worlds (at least 9): 4 primary, at least 6 secondary (moon, titan, 4 jovians, possibly many more jovian and saturnian satellites)<br />icy worlds (at least 6): at least 4 primary (pluto, quaor, sedna, new proposed 10th planet), at least 2 secondary (charon, triton)<br /><br />There are no known tertiary worlds in our solar system, since none fulfil the requirements to become a planet (not large enough to form a sphere). However they could exist in other systems. Planets that exist in open space without a parent sta

 

[jroswald2001]

Here is a classification of the planets based on my last post, listed is the (name;order; radius;mother planet). in recognition that other classes might be discovered, the classes I included are designed to allow other definitions alongside. <br /><br />C-Class - Gas Giants <br /> Jupiter 1 143,128 <br /> Saturn 1 60,268 <br /><br />F-Class - Ice Giants <br /><br /> Neptune 1 25,559 <br /> Uranus 1 24,764 <br /><br />M-Class - Rocky worlds (density /> 1.5) <br /><br /> Earth 1 6378 <br /> Venus 1 6051 <br /> Mars 1 3390 <br /> Ganymede 2 2631 J<br /> Titan 2 2575 S<br /> Mercury 1 2440 <br /> Callisto 2 2400 J<br /> Triton 2 2700 N<br /> Moon 2 1738 E<br /> Europa 2 1569 J<br /> Io 2 1815 J<br /> Titania 2 788 U<br /> Oberon 2 761 U<br /> Ariel 2 580 U<br /> Dione 2 560 S<br /> Ceres 1 480 <br /> Pallas 1 285 <br /> Vesta 1 265 <br /> <br /><br />S-Class - Icy worlds (density < 1.5) <br /> 2003UB313 1 1800 <br /> Pluto 1 1195 <br /> Sedna 1 875 <br /> Rhea 2 765 S<br /> Iapetus 2 730 S<br /> Quaor 1 650 <br /> Charon 2 593 P<br /> Tethys 2 530 S<br /> Enceladus 2 250 S<br /> Mimas 2 200 S<br /> <br />According to this there are in all 32 planets, of which none are zero order, 15 are primary, 17 secondary, and none are tertiary. Of course the entries below 500 km in diameter can be disputed, there are worlds that are irregularly shaped that nevertheless are larger than others with a spherical shape, it gets problematic here and rather grey. <br /><br />If this be regarded as far too generous, an alternative classification could increase the threshold of a planet size to that of a planet in which a clear differentiation of its structure can be inferred (core, mantle, crust etc.). With such a definition objects above a radius of, say, 1000 km are all likely to comply. This reduces the total planet number by 15 to 17, of which 10 are primary and 7 secondary. The distinction between icy and rocky worlds is of course fluid, and may not even be justified, or may call on a subclassification of such

 

[Philotas]

I agree with most of what you say. However, I think the definition of a 'moon' shoulde be kept as it is. If a planet get captured by another, it is now a moon; if a circular shaped moon get`s kicked out of orbit, it`s now a planet. Let`s either divide the moons into primary and secondary moons; primary circular and secundary irregular shaped. Otherwise there isn`t really any point in the defintion 'moon', just call them asteroids since all irregular satelites are captured anyway. Alternatively, call only circular shaped satelites for moons, that way you know that these objects are scientifically interesting and that they orbit a planet. <div class="Discussion_UserSignature"> </div>

 

[igorsboss]

Planet: Having at least 512, but not more than 1023 posts.

 

[Philotas]

Reminds me that I have a long way to go.. <div class="Discussion_UserSignature"> </div>