POLL: How many Planets in our Solar System

[toothferry]

what if a planet like spear is found (9/10 the size of Pluto) there will be lots of pressure to call it a planet too <img src="/images/icons/crazy.gif" />

 

[toothferry]

that makes sense, but there are Lots and Lots of minor planets then.

 

[Philotas]

What I forgot to add to my previous post:<br /><br />Objects to be 'upgraded' to planet status with the definition “A planet is a object orbiting a star with enough mass to gravitationally assume a spherical or ellipsoidal shape”: Ceres, Varuna, Quaoar, Sedna, 2003 EL61 and 2003 UB313; wich gives 15 planets(I forgot to count 2003 EL61 and Sedna earlier). <br /><br />To make it easier for the public to learn the names on the planets one can divide planets into two groups: ‘the major planets’ and ‘the minor planets’. <br />The major planets are the biggest and most important planets in our solar system. They count 8 or 7, depending whether you want to call Mercury major. A new major planet must be bigger than Mecury or Mars, that also depends on ones definition. <br />These are the planets one have to learn about at school and such, because they are the biggest, and so far have their orbits relatively for themselves and doesn`t make up a group, hence they are worthy indiuvidual facts, not like asteroids or KBO`s wich share composition etc.<br /><br />Still minor planets are planets, and not asteroids or comets.<br /><br />This way, the biggest planets can have a worthy planet status for themselves, while we still have a sharp, good scientifically definition for a planet. <br />Once out of our solar system we don`t need major or minor planets, but just planets.<br /> <div class="Discussion_UserSignature"> </div>

 

[vogon13]

Would consider objects that meet a certain number of characteristics out of a list I'm working on to be planets:<br /><br />*solar orbit that calculates out as stable over billion + year time scale (and read this to exclude any object orbiting another planet)<br /><br />*atmosphere (temporary, but periodic atmosphere OK)<br /><br />*spherical to pretty high precision (oblate due to high rotation OK)<br /><br />* satellite(s)<br /><br />* orbit inclined to solar equator less than 22.5 degrees<br /><br />*non-chaotic rotation (sorry Hyperion!)<br /><br />*eccentricity of solar orbit less than .25<br /><br />* orbit around sun, when projected in 2D, does not intersect the orbit of another bonifide planet<br /><br />*has some detectable internal processes (geothermal, volcanic, magnetic field, quakes, geysers, etc.)<br /><br /><br /><br />Well, that's a list of 9 characteristics. May think of others later.<br /><br />But for now, am thinking any object that has 5 or more characteristics (I might say 6 in the morning) from the list is a planet.<br /><br />Think that list would make Pluto a planet, and the new objects are in limbo till we get more information.<br /><br />IOW, we don't have to decide the planet thing now and can foist the inevitable controversy on a later generation.<br /><br /><img src="/images/icons/wink.gif" /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[lunatio_gordin]

<font color="yellow">* orbit around sun, when projected in 2D, does not intersect the orbit of another bonifide planet </font><br />That makes pluto not a planet, doesn't it?

 

[vogon13]

Pluto meets enough of the other criteria (5 out of 9, or maybe 6 out of 9, I can't decide) to retain planethood.<br /><br />So does Mercury, despite lack of atmosphere. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[vidar]

I am sorry that I can not vote on this poll.<br />Since Mercury is smaller than moons Ganymede and Titan, I think Mercury is a moon too.<br />Therefore there are seven planets in our solar system.<br />

 

[teije]

I'll go nasty and go with the ancient greek definition.<br /><br />5 planets. <br /><br />- It's a light thingy in the sky that moves different from the other light thingies.<br />- It's not the sun or the moon<br />- It's naked eye visible (the greeks didn't have any other way after all.)<br /><br />That gives me Mercury, Venus, Mars, Jupiter, Saturn. NB: not even Earth would be considered a planet by that definition. <img src="/images/icons/laugh.gif" /><br /><br />Ok ok, I know it's trivial, but IMHO all the other definitions are just as trivial really.<br />Teije

 

[Philotas]

That`s diffusing the definitions. A moon is an object at any size orbiting a planet, a star hence can`t have a moon. And what if an object bigger than Mars, or maybe even the Earth is found orbiting a gasgiant? <br />Then Earth wouldn`t be a planet any longer, or what? <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[vidar]

This is discussed under the topic: Definition of "planet".<br />My view is that it’s not the position that determines whether it is a planet or moon, but rather its properties. A moon can be knocked out of its orbit. That’s what I think has happened to Pluto and Mercury.<br />

 

[craigxc]

I go with 11:<br />Mercury,venus,earth,mars,<br />jupiter,ganymede,callisto,<br />saturn,titan,<br />uranus,<br />neptune.<br /><br />That's all there are that are over 4500 Km in diameter, and I don't care where it orbits. Anything smaller than 4000-4500 Km is a moon or an oid. Ganymede, Callisto and Titan don't get 1/10th the recognition they deserve just because they orbit other planets. Pluto, 1/3 the size [volume] of Earth's moon, can be no more than a moon, and in fact everything known So Far beyond Saturn except Uranus and Neptune, if all squashed together, wouldn't add up to a Callisto or a Mercury, much less a Titan or a Ganymede.<br /><br />Any double definition (orbit and size) will get into trouble because there will be things that are included by one ctriterion and excluded by the other.<br />

 

[toothferry]

I thought this thread would be a great place to write message #512. I think that means that <b>now I'm a planet!</b><br /><br />add another to the list <img src="/images/icons/cool.gif" />

 

[vidar]

The planet toothFerry?<br />It can not be as big as Mars, Jupiter, Neptune and the others named after gods?<br />

 

[Philotas]

It can actually be big enough to be spherical though, looking at one of the latest names of a big KBO. <div class="Discussion_UserSignature"> </div>

 

[mrmux]

You're all wrong. There's only one real planet - the rest are just wannabes...<br /><br />(official statement from the Jovian government)

 

[jatslo]

Why can a star orbit a star, but a planet cannot orbit a planet?

 

[toothferry]

<img src="/images/icons/laugh.gif" /> hey.. ToothFerry is a God too.. just not a Greek one <br /><br />Planet ToothFerry.. yes, that works just fine for me. <img src="/images/icons/cool.gif" />

 

[TheShadow]

The International Astronomical Union, THE authority on the cataloging and naming of astronomical objects has no plans to reclassify Pluto. Their Press Release reads in part:<br /><ul type="square">The Status of Pluto: A clarification <br />Lately, a substantial number of smaller objects have been discovered in the outer solar system, beyond Neptune, with orbits and possibly other properties similar to those of Pluto. It has been proposed to assign Pluto a number in a technical catalogue or list of such Trans-Neptunian Objects (TNOs) so that observations and computations concerning these objects can be conveniently collated. This process was explicitly designed to not change Pluto's status as a planet.</ul><br /> <div class="Discussion_UserSignature"> <p> </p><p> </p><p> </p><p> </p><p><font size="1" color="#808080">Who knows what evil lurks in the hearts of men, the Shadow knows. </font></p> </div>

 

[vidar]

I do think a planet can orbit another planet.<br />Titan and Europe are two examples.<br />

 

[vidar]

Well I know ToothFerry is a skilled alchemist making golden coins out of teeth.<br />That might qualify for devine properties.<br />However, a star named ToothFerry, will not do.<br />

 

[Philotas]

<blockquote><font class="small">In reply to:</font><hr /><p>I do think a planet can orbit another planet. <br />Titan and Europe are two examples.<p><hr /></p></p></blockquote><br /><br />Yes it can, Triton and Charon being the best examples known this far. But a planert orbiting another planet is under the term 'moon', not planet. If it gets kicked out of its orbit around the planet it becomes a planet once again.<br /> <div class="Discussion_UserSignature"> </div>

 

[vidar]

It all comes down to this ancient definition of planet.<br />I think you are right per definition.<br />However, I point out that the definition is inaccurate about the objects’ properties.<br />

 

[toothferry]

<img src="/images/icons/laugh.gif" /> agreed. although TheShadow could also have become a cool name for an outer planetoid (or planet).. ..though it looks like we will remain stuck at 9 named planets.

 

[vidar]

No! You weren’t supposed to agree.<br />I think you have the potentials to be a star, at least in this discussion board.<br />TheShadow could even be a black hole (dark star).<br />

 

[pluto_vic]

Methinks Kuiper Belt objects can be planets too, just of a different classification, like the jovian & rocky planets. Except we shouldn't really talk about them as such, as there are many. Btw, I wouldn't classify Jupiter as a planet, but rather a brown dwarf. I guess this would mean its moons could be called planets. And the number of planets you ask? Approaching 80. There would have to be some point where anything further out is an asteroid, comet, meteor, its obit is too irregular and unpredictable...