[X] My Assistant

[dvandorn]

Aw, shoot -- and here I had in mind a concept whereby these out-of-plane objects could be classified based on a certain degree of extra-solar composition. I had this image of the objects in the Kuiper Belt and Oort Cloud being condensed out of the interaction between the T-Tauri stage of the solar wind and the supernova remnant gasses and particles into which this energetic solar wind slammed... as such, they would be of a compositional mix between the solar nebula and the surrounding supernova nebula from which the Sun and its planetary nebula evolved.

Since the T-Tauri stage of the solar wind would have pushed out in all directions, it would have established a spherical structure around the Sun of the remnants of the interactions between the wind and whatever it pushed into and through on its way out. That would seem to be the perfect structure from which to derive the KBOs and OCOs, would explain why they occupy a space defining a spherical cloud around the Sun, and would suggest that these objects might be of somewhat different composition from the rest of the solar system.

Granted, all of this extrasolar material ought to similar to the materials derived from the planetary nebula, since the solar system was formed from a piece of the original supernova nebula. But it was my thinking that the extrasolar gasses and ices included in the KBOs and OCOs could let us characterize differences between the planetary nebula (from which the solar system was derived) and the surrounding supernova remnants. Isotopic abundance information would be extremely interesting, I bet...

But if all of these objects were originally formed from the planetary nebula disk and were later ejected into this spherical cloud, then my theory is non-applicable... darn it!

-the other Doug

[Mongo]

I do rather like Mike Brown's definition of a planet as an object, by far the largest in its own neighborhood. in a solitary orbit (not part of a recognised population of objects). I am copying an extract from his definition at:

http://www.gps.caltech.edu/~mbrown/sedna/

Just like the solar system very naturally divides itself between round objects and non-round objects, it also very naturally divides itself between solitary individuals and members of large populations. The best known example of a large population is the asteroid belt. We call it a population because one region of space contains objects with a continuous range of sizes from one moderately large object (Ceres) to a handful of slightly smaller objects (Vesta, Pallas, Hermione) to a huge number of extremely small objects (rocks, dust particles). The solitary individuals are much different. In their region of space there is only them (Earth, say) and then a collection of much much smaller objects (the near-earth asteroids), with no continuous population in between. A single example helps to dramatize the difference between a continuous population and a solitary individual. Ceres, the largest asteroid, has a diameter of 900 km. The next largest asteroid, Pallas, has a diameter of 520 km. After that is Vesta at 500 km, and Hygiea at 430 km, and the list continues on down. The jump in size between asteroids is never more than a factor of two. In contrast, the earth has a diameter of about 12,000 km, while the largest other object in the earth's vicinity, the asteroid Ganymed, has a diameter of about 41 km, a factor of 300!

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune all count as solitary individuals by this definition. Pluto and Quaoar do not. Pluto is clearly a member of the Kuiper belt population, as can be seen from the fact that there are objects in the same vicinity slightly smaller than Pluto (Quaoar, 2004 DW, Varuna), and then even a larger number slightly smaller than that, and then on down.

[...]

Since there is a clear scientific distinction between solitary individuals and members of large populations it is instructive to come up with words to describe these objects. The large populations can each be described by the particular population (asteroid belt, Kuiper belt, inner Oort cloud, Oort cloud). What about the solitary individuals? Isn't the best word to describe them "planet"?

[...]

Is there any historical basis for saying that a planet is a solitary individual that is not a member of a large population? Yes! As mentioned earlier, historically Ceres and the first few asteroids were initially classified as planets. Only when it became known that there were many many asteroids in similar orbits was it decided that they should no longer be classified as planets. Historically, there is a clear distinction between planets and populations. Any definition which fails to make this distrinction is in strong trouble on historical grounds. This simple look at history shows that Pluto is completely analogous to Ceres. Pluto was initially thought to be a solitary individual. Over time we found more objects in the vicinity and realized instead that it is a member of a large population. Historically, then, Pluto, too, should no longer be considered a planet.

We are thus left with a final concept of the word planet. Every object in the solar system quite naturally can be classified as either a solitary individual or a member of a large population. The individuals are planets. The populations are not. This definition fits the historical desire to distinguish between asteroids and planets, and this definition fits all of the requirements of scientific motivation.

Bill

[Guest_BruceMoomaw_*]

"In contrast, the earth has a diameter of about 12,000 km, while the largest other object in the earth's vicinity, the asteroid Ganymed, has a diameter of about 41 km, a factor of 300!"

Yeah, but now you have to define "vicinity". Are Mercury, Venus and Mars in Earth's "vicinity" or not? Conversely, let us suppose that the Kuiper Belt actually consisted of exactly one solar-orbiting object in a really weird orbit vastly different and very distant from the eight previously recognized planets -- but that object was only 3 feet across. Would it therefore be labeled a "planet"? I think not.

We really need to face facts: ANY criterion we use to try to define "planet" -- or "moon" -- will be crammed with unavoidable ambiguity and arbitrariness. (It's also increasingly clear that the same thing applies to our attempt to firmly separate "asteroids" from "comets", at least when the possible comets are so far from the Sun that no material is sublimating off them to allow us to tell how much of them is ice and how much is rock.) The situation is entiely different from the star/brown dwarf/planet distinction, where we do have a nice firm divider: brown dwarfs are big enough to fuse deuterium but not big enough to fuse regular hydrogen.

[Guest_Myran_*]

Alan Stern said: And as to Sedna and Pluto and UB313, as best we can tell, they were accreted just like Earth, Mars, etc., but aborted early in their growth.

Isnt that true for the asteroids also? In that case the most popular theory seems to be that the interaction with Jupiter prevented further growth, but the asteroids still had started on the same accretion process.
While talking about the asteroids one can note that 2003 UB313 have an inclination of 44% to the ecliptic, and that fact makes me think of one asteroid again and thats the 35 degree inclination of Pallas.

That Pluto have a moon have been used as part of the argument to keep its planetary status, but again, both asteroids as KBO's have turned out to have secondary objects as well.

I was beaten by Mongo on the last part of this reply, and that is that planets are solitary bodys in their orbits, whereas the asteroids belong to a group. The same appear to be true for the KBO's.

So the bottom line before I make my final post to this discussion are that whats said above are the reasons I found the declaration that 2003 UB313 is a 'newly discovered planet' to be quite inappropriate.

[Jyril]

In my opinion, large Kuiper Belt objects (including Pluto) do not qualify as planets. However, it sounds awkward to call them asteroids, because a typical asteroid/KBO is just a mostly unalterd chunk of rock or ice. Instead of asteroids, at least some of these larger bodies have much more complex geological histories and internal structures. Instead, there should be some term to define those miniplanets.

Someone (was it Brown?) proposed that they should be called "planetoids". Nobody really uses that term for asteroids anymore, and it describes them nicely as "planet-like".

[Alan Stern]

Bill--
You're back to that old location argument, which realtors like but few scientists do.
(Yes,Mike Brown is one of the ones who does, to my amazement.).

A real problem with the argument you like is that "a planet" is just the biggest thing
around., and nothing more. That means a planet has no properties other than mass.
So would a big spaceship (I mean BIGGGGG) count? How about a star? A black hole
in a planetary system? By the definition Brown expouses, they would be planets.

And even if you rule these out by demaning it be naturally created and not doing
fusion for a living, you have two other problems to overcome. First, as we learned in
the 1990s, migration is a very important dynamical process for planetary systems--
i.e., objects move about, particularly early and late in the evolution of the system
(when the parent star is young and when it is a red giant).

This kind of movement can cause Earths to move from orbits like ours to be Jupiter
crossing-- would that suddently cause Earth to be declassified as a planet in your
fave scheme. To me this is patentely undesirable. Worse, you say you want to
classify objects as to whether or not they are an individual or part of a big population,
but Earth is embedded in the NEA and Jupiter carries with it about 10^5 Trojans, so
neither is an individual at all.

[Guest_BruceMoomaw_*]

Back in the 1980s, Isaac Asimov proposed that comet nuclei be renamed "cometoids". This didn't catch on, but it would seem to be one promising approach to the KBO nomenclature problem -- except that, without getting very good analyses of their compositions, we genuinely can't tell whether objects far enough from the Sun to be frozen are made mostly out of ice or rock, and dynamics simulations suggest that several percent of KBOs really may be rocky asteroids that wandered out of the inner System.

[Mongo]

This kind of movement can cause Earths to move from orbits like ours to be Jupiter
crossing-- would that suddently cause Earth to be declassified as a planet in your
fave  scheme. To me this is patentely undesirable. Worse, you say you want to
classify objects as to whether or not they are an individual or part of a big population,
but Earth is embedded in the NEA and Jupiter carries with it about 10^5 Trojans, so
neither is an individual at all.

Well, if Earth were put into a Jupiter crossing orbit, it would presumably either eventually collide with it, or be ejected from the solar system, and in either case, the issue of whether it was a planet would not arise. *grins*

According to Mike Brown's suggested definition, the presence of a population of much smaller objects in the vicinity of a much larger object does not affect the much larger object's 'major planethood' status, so neither NEOs (in the case of Earth) nor Jupiter Trojans (in the case of Jupiter) are relevant to their status as major planets, as there is a major difference in diameter and mass.

I would also discount trojan objects as being true planets, whatever their size, as they are clearly in a close dynamical relationship with their 'primary' -- not as directly as with a satellite, but still tied to its gravitational influence. In any case, the maximum stable mass of a trojan would be well below the mass of its 'primary', if I am not mistaken.

Having said all this, I am not married to Brown's definition either. It should be possible to cobble together something that works for our planetary system, but it will be harder to come up with something that works for all planetary systems. Heck, I am no fan of the current nomenclature for naming extrasolar planets! Talk about illogical...

This is getting off-topic, but the current system is crazy. In multi-planet systems, we are seeing that the planets are given letters in the order of their discovery, which leads to random orders within the planetary system. I think that A, B, C should be restricted to stars, as they had been for decades. With the planets so far discovered, the one datum almost always found, other than their mere existence, is their orbital period -- and even when the exact period is not yet known, it can be estimated. Why not tie the planet name to that? I am thinking in particular of using the common logarithm of the planet's orbital period in days, so that (for example) a planet, orbiting HD 123456, with a period of 3.2 days, would be called HD 123456 p05, and its neighbor with a period of 800 days would be called HD 123456 p29.

For a specific example, take the 55 Cnc system:

55 Cnc E -- p = 2.81 days
55 Cnc B -- p = 14.67 days
55 Cnc C -- p = 43.93 days
55 Cnc D -- p = 4517.4 days

This could be changed to:

55 Cnc p04
55 Cnc p12
55 Cnc p16
55 Cnc p37

Which would have the advantage that the planets in a planetary system would always be sortable by period (and semimajor axis), with no other information needed other than their designations.

I doubt that it will ever happen, though, as the current system of nomenclature has become fairly well-established, despite its evident flaws.

Bill

[Guest_BruceMoomaw_*]

It now looks like 2003 FY9 is bigger than originally reported.  The original MPEC circular listed H = 0.1, but its absolute brightness was increased today to H = -0.4 (compared to Pluto at H = -0.5).

Given any plausible albedo, this would also mean a diameter in excess of 2000 km.

So we now know of three TNOs with diameters greater than 2000 km:

2003 UB313  H = -1.1  D = 2600-3200 km
Pluto  H = -0.5  D = 2390 km
2003 FY9  H = -0.4  D = 2200-2500 km (personal guestimate)


Bill

Where'd you get this information, Bill? It isn't yet in the Minor Planet Electronic Circulars.

[Guest_BruceMoomaw_*]

By the way, it's "2005 FY9", not "2003 FY9".

[Mongo]

Where'd you get this information, Bill?  It isn't yet in the Minor Planet Electronic Circulars.

There was a post at mpml today from SFJCody that the newest MPEC daily orbit update gives an H value of -0.4 for this object (yes it is 2005 FY9, of course -- mea culpa). The circular is here, and the changed information is about 3/4 of the way down the list:

K05F06F 16.8 0.15 K058I 89.885 323.875 169.168 3.014 0.06214 2.26700 3 X
K05F07Q 17.0 0.15 K058I 42.784 15.107 157.245 14.384 0.18256 2.69019 2 X
K05F09Y -0.4 0.15 K058I 199.428 256.589 79.412 28.999 0.14117 45.58983 2 X
K05G13Y 14.7 0.15 K058I 316.249 203.539 89.030 12.347 0.13933 3.22548 2 X
K05G30F 15.8 0.15 K058I 294.161 232.095 77.869 6.996 0.11826 2.42330 5 X

Bill

[deglr6328]

Getting away from the planet/KBO/TNO debate for a minute....

do we have enough data yet on the KB region to make valid statistical guesses on the size distribution of the objects we're likely to find there? What about the Oort cloud? Is it reasonably possible to find a near Earth size object eventually? There was an idea from David Stevenson at Caltech in the late '90s that TOTALLY fascinated me and since then has always stuck in the back of my head when thinking about these (very) far out objects. He calculated that for ~Earth mass objects floating in interstellar space with Kbar surface pressures, liquid water oceans are possible. I often wonder if this idea can't be applied to large KBOs which we may (or very well may not?) find.

[Alan Stern]

These new guys are lilely to not be KB but instead Oort Cloud members. In any case,
there are very good arguments, I think, that there should be objects up to at
least Earth size, possibly a couple of times that, out there int he OC. See my 1991
paper: On the Number of Planets in the Solar System: Evidence of a Substantial
Population of 1000-km Bodies. Icarus, 91, p271, 1991. This paper predicts
both the find made today and much larger finds. One argument worth noting
for the really big guys is that to achieve the tilts of Uranus and Neptune, you need
collisions with objects of 2-5 Earth masses, and for every object that hit U and N,
several get ejected in near-miss collisions..

[deglr6328]

Cool! I will have to wait to read your paper in icarus when I get abck to work monday, where I have access.

[Guest_BruceMoomaw_*]

In our little private "Planetary Sciences" webgroup, Ron Baalke quoted Mike Brown himself as saying yesterday: "Based on Spitzer measurements, 2005 FY9 is confirmed to be smaller than Pluto." Unfortunately, he didn't say how much smaller. But at any rate the Revolution is now upon us: depending upon what size you use as a dividing line, the Solar System no longer has 9 known planets. It now has 10 or 11, or else it has 8, or else (if you follow Alan Stern's lead) it has a hell of a lot more. What we are really going to have to tell the schoolkids, of course, is that the question from now on will be forever ambiguous.