IAU looking to decide if 2003 UB313 is a major planet

[CalliArcale]

I realize some folks may already have seen this, but I only just found it, so I'm posting it. <img src="/images/icons/wink.gif" /> The IAU has formed a working group to decide once and for all what the definition of a major planet is. It appears that they are intending a definition based on size. Until that working group has made a decision, they will not be issuing a name for 2003 UB313, because it will affect how it is named. If it's a minor planet, they will consider the undisclosed name suggested by the discoverers of 2003 UB313. If it's a major planet, they will name it themselves after forming another committee to come up with a name. Apparently they have already decided that if it's a major planet, it should get a name from Greco-Roman mythology. Unfortunately, the vast majority of those are already taken by moons and minor planets, so this could get interesting.<br /><br />Here's what the IAU said on the subject:<br />IAU / FAQ / Trans-Neptunian Object 2003 UB313<br /><i><b>Trans-Neptunian Object 2003 UB313 vying with Pluto in Size</b><br /><br />IAU Circular 8577 announced on July 29, 2005 the discovery of three relatively bright Trans-Neptunian objects by M. E. Brown, C. A. Trujillo, and D. Rabinowitz using the Palomar 1.2-m Schmidt telescope. One of these objects, 2003 UB313, appears to be as big as or slightly bigger than the planet Pluto. The object's distance from the Sun varies between about 38 AU (1 AU is 150 million kilometers) and 98 AU, which is also close to its current distance. Its orbit has a period of about 560 years and is even more elongated and more inclined than the orbit of Pluto (let us here make a link to: http://www.gps.caltech.edu/~mbrown/planetlila/index.html).<br /><br />We repeat below an earlier announcement of an IAU Working Group for establishing a definition of a planet. Th</i> <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[vogon13]

Last decent rest area, if nothing else, between here and Barnard's star.<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>

 

[mikeemmert]

If objects are going to be classified as planets according to their size, there has been a consistent trend to overestimate the size of TNO's by assuming a low albedo. This has led to several false alarms about "HUGE NEW OBJECT FOUND!" and they turn out to be asteroid sized. Pluto was imagined to be very dark black when it was thought it had enough mass to yank Neptune around.<br /><br />There has been quite a bit of methane ice found on these objects. In the lab, methane darkens into tholins under ultraviolet light, which are a dark red. Why doesn't this happen in the outer solar system? It's puzzling. Maybe methane ice traps hydrogen released by the decomposition of the methane and recombines wiht the tholins? Does the ice trap solar wind particles, which are mostly hydrogen? I don't know. If the lab tests are not using solidly frozen methane, that might be a problem.<br /><br />I would like to comment that according to Mike Brown's best guess as to the diameter of 2003 UB313, it is almost exactly the size of Triton. I don't think this is a coincidence (See "Is 2003 UB313 the Lost Moon of Triton?). <br /><br />I ran into the name "Beelzebub" whilst googling "Lagrange objects". That was from an entry into the Catholic Encyclopedia. It had nothing to do with astronomical objects, in fact, "objects" was used as a verb in that article, as if Mr. Lagrange (probably not the same one, but maybe) were an attorney, objecting to a point about the name "Beelzebub".<br /><br />The "Ba'al of Zebub" is the Lord of the Flies in a Philistine religion and was meant to insult the Philistines (it actually refered to the ba'al [god] of Accaron or Ekron). Later this was incorporated into Catholic philosophy as the Lord of the Nether Regions, which morphed into the underworld. He was supposedly Satan's brother.<br /><br />Since Mike Brown hinted that he was going to go to another mythology, I was afraid he was going to use the most big-time Lord of Darkness left. That might ca

 

[Philotas]

In this solar system, every celestial body that is round and that orbits the Sun should be called a planet. In other solar systems we`re going to have to make more 'advanced' definitions. <div class="Discussion_UserSignature"> </div>

 

[CalliArcale]

The IAU does consider any non-star orbiting a star to be a planet. They have not yet made an official ruling on whether freefloating nonstar bodies can be called planets, for instance. What's significant for this discussion isn't whether or not 2003 UB313 is a planet -- it's whether it's a <i>major</i> planet or a minor one. The IAU also has not formally ruled on whether or not Pluto is a major planet. Indisputedly, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune are defined by the IAU as major planets. Pluto is in semantic limbo. Most everything else orbiting the Sun (such as 1 Ceres, 433 Eros, Comet Halley, etc) is a minor planet. (One exceptoin: the very few manmade satellites of the Sun are not considered planets of any kind. Also there is no set lower limit on the size of a minor planet.) <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[Philotas]

Then I say that every celestial body that is round and that orbits the Sun should be called a <i>major</i> planet. I can`t see how they can put circular objects, as for example Ceres and Sedna, under the same defintion as irregular objects, as f. ex. 951 Gaspra and Itokawa. Round objects has the ability to capture atmospheres and to be geologically active, while irregular objects hasn`t. The defintions that they are making now is very unfair to the round bodies in our solar system that are too small to be called major planets, they should have been distinguished in <i>some</i> way. <div class="Discussion_UserSignature"> </div>

 

[vogon13]

I see the nomenclature situation as even more complex.<br /><br />What's Dactyl?<br /><br />What would you call Dactyl should its' host Ida wind up orbiting Jupiter as a moon?<br /><br />If somehow, it is determined that Polydueces started off as a primordial satellite of Dione, but now has a Trojan relationship with Dione and Saturn, what is it?<br /><br />What if Triton is determined to be demonstrated as a former 'planet' captured by Neptune, should its classification be unique?<br /><br />What if Jupiters' outer satellites are determined to consist of 3 populations, primordial objects that formed contemporaneously with Jupiter, captured main belt asteroids, and captured Trojans from Jupiters' L4 and L5 positions? Are they all 'just' moons? What do we call their satellites (should any be discovered) ?<br /><br />It may be possible that the Valhalla and Asgard structures on Callisto are the craters from a former Callistoan Lagrange object <i> that had a satellite </i>! What is the satellite of a Lagrange object orbiting a planet? Orbiting the sun?<br /><br /><br /><br />Yoiks! What a mess! What do we call all this stuff?<br /><br /><img src="/images/icons/wink.gif" /><br /><br /><br /><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>

 

[Philotas]

Triton is easy, just call it a moon. If Ida starts orbiting Jupiter you call Dactyl a Jovian asteroid, as all the other irregulary objects orbiting Jupiter should have been called. They don`t need to be distinguished.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>What if Jupiters' outer satellites are determined to consist of 3 populations, primordial objects that formed contemporaneously with Jupiter, captured main belt asteroids, and captured Trojans from Jupiters' L4 and L5 positions? Are they all 'just' moons? What do we call their satellites (should any be discovered) ? <br /><p><hr /></p></p></blockquote><br /><br />We don`t distinguish between circular moons that have formed differently, so there`s no need to distinguish here either. The first use of the term 'moon' was on our Moon wich was created after a giant collision, and if I remember it correctly, a great part of it consist of former Earth-material. So far we have not found anything like that, yet we call objects orbiting other planets for moons.<br /> <br /><blockquote><font class="small">In reply to:</font><hr /><p>It may be possible that the Valhalla and Asgard structures on Callisto are the craters from a former Callistoan Lagrange object that had a satellite ! What is the satellite of a Lagrange object orbiting a planet? Orbiting the sun? <p><hr /></p></p></blockquote><br /><br />It is orbiting the langange object, hence a moon.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>If somehow, it is determined that Polydueces started off as a primordial satellite of Dione, but now has a Trojan relationship with Dione and Saturn, what is it? <p><hr /></p></p></blockquote><br /><br />A moon.<br /><br />See, it wasn`t all that difficult, was it? <img src="/images/icons/wink.gif" /><br /> <div class="Discussion_UserSignature"> </div>

 

[vogon13]

So, to see if I have it right;<br /><br />A marklar orbiting a marklar is a marklar.<br /><br />A marklar that used to orbit another marklar, but now is around a different marklar is still a marklar.<br /><br />Marklars that were marklars around other marklars, even it they have marklars of their own, are still marklars.<br /><br />Whether a marklar is around another marklar or not, if it has a marklar, or had a marklar, even if it wasn't a marklar then, it is still a marklar?<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>

 

[Philotas]

You have it right when it comes to asteroids, but not when it comes to planets.<br /><br />A planet is a round celestial body orbiting the Sun. A moon is a round celestial body that orbits a planet. An asteroid is an irregular celestial body(and that isn`t a comet).<br /><br />Planets cannot have planets.<br />Planets can have moons.<br />Planets can have moons that have moons/asteroids that again may have moons/asteroids.<br />Planets can have asteroids.<br />Planets can have asteroids that have asteroids that again may have asteroids.<br />Asteroids can have asteroids.<br />Asteroids can have asteroids that again may have asteroids.<br /> <div class="Discussion_UserSignature"> </div>

 

[vogon13]

clue (kloo), <i>n</i>., <b>1.</b> a guide in the solution of a problem, mystery, etc.<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>

 

[mikeemmert]

Replying to "Then I say that every celestial body that is round and that orbits the Sun should be called a major planet."<br /><br />Let's see...Earth has mountains up to five miles high and an equatorial bulge. 2003 EL61 is big, but because of it's two hour axial spin, it's shaped like a fat cigar.<br /><br />Define "round".

 

[CalliArcale]

Personally, I think they should go by mass. It's more significant in terms of celestial mechanics. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[aaron38]

I also think that the major planet class should be limited to objects with little inclination to the orbital plane of the solar system.<br /><br />An inclination of 10 and 17 degrees that Ceres and Pluto have respectively should make them minor planets.<br /><br />However, I would give Pluto some sort of "dual citizenship". It's messy to correct ingrained historical mistakes.

 

[Philotas]

By round I mean that the object has big enough gravity to pull itself into a <i>roughly</i> spherical shape; it`s not irregular like asteroids. I haven`t heard any news about that they are 100% sure that 2003 EL61 is cigar-shaped, but I don`t really consider it a planet if it is.<br /><br />While Earth may have 8km high mountains and an equatorial bulge, it`s mass roughly distributed even between south, W, E and north, while asteroids might have 45% of their mass distributed to both E and W and only 5% each to N and S, if you get what I mean. <div class="Discussion_UserSignature"> </div>

 

[Philotas]

<blockquote><font class="small">In reply to:</font><hr /><p>An inclination of 10 and 17 degrees that Ceres and Pluto have respectively should make them minor planets.<p><hr /></p></p></blockquote><br /><br />Mercury have an inclination of 7 degrees, shouldn`t that also make Mercury a minor planet? 7 degrees is 3 degrees higher than Venus, the next planet on the "ranking". Ceres is also 3 degrees from the planet "above", shouldn`t that make Ceres a planet? <div class="Discussion_UserSignature"> </div>

 

[formulaterp]

Just make it simple:<br /><br />Pluto = Planet<br /><br />Bigger than Pluto = Planet<br /><br />Smaller than Pluto = Space Rock

 

[Philotas]

According to that definition, our Sun is a planet...<br />--<br />It`s not more simple than the spherical definition really, less controversy with the public perhaps. <div class="Discussion_UserSignature"> </div>

 

[formulaterp]

So be it. <img src="/images/icons/tongue.gif" />

 

[CalliArcale]

Personally, I vote for less controversy with the public. This is a semantic issue, and really won't affect science at all. But when it comes to language, there are some battles that can't be won. If most people think Pluto is a planet, we're stuck with it. (Dictionary writers understand this; they write their definitions to reflect actual useage, not to impose new useage.) <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[Philotas]

I don`t completely agree with you there. If Ceres had kept its status as a planet, NASA had visited it so that they could say: "We`ve visited every planet in the inner solar system. "<br />I bet they had. <div class="Discussion_UserSignature"> </div>

 

[mikeemmert]

CalliArcale wrote:<br /><br />"Personally, I think they should go by mass. It's more significant in terms of celestial mechanics."<br /><br />What if it has no observable moon? How would you measure the mass?<br /><br />I'm aware of Pluto's new moons. However, there may be Sedna-like objects out there. The source of this object is a mystery (I like the brown-dwarf-shedding-objects theory but haven't really looked at it hard).<br /><br />If Sedna has a moon, good luck finding it. On the other hand, any object big enough to warrant consideration as a planet can probably be seen by Spitzer or a successor.

 

[mikeemmert]

Thanks for your answer, Philotas, but we would need a more precise definition under your scheme.<br /><br />Jupiter is an oblate spheroid, so would it be a planet? We may find other rapidly rotating objects, which may be distorted into something that is not really a sphere. 2003 EL61 is a very good case in point, thanks for bringing it up. <br /><br />I would favor an arbitrary definition based on diameter, which is the easiest quantity to measure. Something like "2000 km in it's shortest dimension".<br /><br />

 

[vogon13]

They are all Marklars.<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>

 

[mlorrey]

I think there should be a distinction between classifying an object by its mass/composition versus how or what it orbits. Essentially anything rounded by its own gravity should be a planet. Anything of insufficient gravity to do so is either an asteroid or a comet, depending upon its composition. Any of these objects can be moons of planets. A moon is any kind of natural satellite of a planet .