Paper: astro-ph/0512075

Date: Sat, 3 Dec 2005 07:44:54 GMT (148kb)

Title: Three-Body Affairs in the Outer Solar System

Authors: Yoko Funato, Junichiro Makino, Piet Hut, Eiichiro Kokubo, Daisuke
Kinoshita

Comments: Published in 2003 in the proceedings of the 35th Symposium on
Celestial Mechanics. 8 pages

Journal-ref: In Proceedings of the 35th Symposium on Celestial Mechanics, eds.
E. Kokubo, H. Arakida, and T. Yamamoto. Tokyo, Japan, 2003
\\
Recent observations (Burnes2002,Veillet2002,Margot2002a) have revealed an
unexpectedly high binary fraction among the Trans-Neptunian Objects (TNOs) that
populate the Kuiper Belt. The TNO binaries are strikingly different from
asteroid binaries in four respects (Veillet2002): their frequency is an order
of magnitude larger, the mass ratio of their components is closer to unity, and
their orbits are wider and highly eccentric. Two explanations have been
proposed for their formation, one assuming large numbers of massive bodies
(Weidenschilling2002), and one assuming large numbers of light bodies
(Goldreich2002). We argue that both assumptions are unwarranted, and we show
how TNO binaries can be produced from a modest number of intermediate-mass
bodies of the type predicted by the gravitational instability theory for the
formation of planetesimals (Goldreich and Ward1973). We start with a TNO binary
population similar to the asteroid binary population, but subsequently modified
by three-body exchange reactions, a process that is far more efficient in the
Kuiper belt, because of the much smaller tidal perturbations by the Sun. Our
mechanism can naturally account for all four characteristics that distinguish
TNO binaries from main-belt asteroid binaries.

\\ ( http://arXiv.org/abs/astro-ph/0512075 , 148kb)

Discovery of a large Kuiper Belt object with an unusual orbit

2005 FY9 is back to -0.4 again.

K05F09Y -0.4 0.15 K0636 147.115 296.397 79.555 28.999 0.15503 45.70616 9 X

To be smaller than 2000km in diameter with this absolute magnitude requires an albedo >63%... it would be interesting to know what constraints the Spitzer non-detection puts on lower values of the albedo. This thing is either v. big or v. shiny.

I know!... It's made of Tinfoil!

<adjusts his microweave tantalum-fiber whole-head skimask -- the latest in high-tech paranoid headwear>

Returning to the discussions regarding the classification of the more-or-less spherical wossisnames which orbit around other things (sometimes known as planets, or not, as the case may be), I came across one of the more, er, 'rational' discussions the other day, and it set me thinking. The point was made that you could divide planets into small worlds and big worlds, and the small worlds neatly divided into rocky worlds and ice worlds. The big chaps were, of course, the gas giants. So, for the small worlds, you have nice rocky guys close to the Sun, and ice chaps further out, no matter whether they orbit the Sun or something else. Then I thought of a fly in the ointment: there's actually an outer planetary rock world, with precious little in the way of water.

So, do we call Io a rock world, or a dehydrated ice world?

Just goes to show how rapidly even 'sensible' categories fray around the edges!

Bob Shaw

And it appears if we watch long enough, eventually Enceladus will run out of E-ring replenishment materials, and then we will have a rocky or metallic object orbiting Saturn.

{granted the time scale for this is rather on the longish side}

I've put together a plot showing all the bodies in the solar system more massive than asteroid (511) Davida (except for TNOs other than Pluto & Charon, will add those later):


The red line is the mass/density profile of a body composed of pure hydrogen at 5AU. No objects (aside from fluffy hot jovians) can exist above the red line.

Any catagorisation based on composition (icy, rocky, metallic etc) will have to have density boundaries that curve to the right with increasing mass, just like the profile for a pure hydrogen body. This is due to the effects of gravitational compression.

An interesting paper on 2005 FY9:

http://www.edpsciences.org/articles/aa/pdf...hj131_forth.pdf

Interesting way of looking at them big round(ish) chaps! Now, if you can just get Bode's Law in there as well...

Bob Shaw

Spitzer observed 2005 FY9 on 22 December:

http://ssc.spitzer.caltech.edu/approvdprog...lan/week109.txt

and (90482) Orcus on the 15th

http://ssc.spitzer.caltech.edu/approvdprog...lan/week108.txt

My attempt at a categorization system based on mass

A solar system inventory

Stars: 1 (Sol, Type G2V)

Brown dwarfs: 0

Gas giants/ice giants: 4
Jupiter
Saturn
Neptune
Uranus

Tier Zero worlds: 0

Tier One worlds: 9
Earth
Venus
Mars
Mercury
Ganymede
Titan
Callisto
Io
Luna

Tier Two worlds: 13+
Europa
Triton
Pluto
Titania
Oberon
Rhea
Charon
Iapetus
Ariel
Umbriel
Dione
(1) Ceres
Tethys
+other TNOs (2003 EL61, 2005 FY9, 2003 UB313...)

Tier Three worlds: 3+
Enceladus
Miranda
Mimas
+TNOs

Tier Three irregulars: 21+
(4) Vesta
(2) Pallas
(10) Hygiea
Proteus
(511) Davida
(704) Interamnia
Nereid
(3) Juno
(16) Psyche
(6) Hebe
(624) Hektor
(87) Sylvia
Hyperion
(7) Iris
(324) Bamberga
Elara
(15) Eunomia
Amalthea
Phoebe
Himalia
(45) Eugenia
+TNOs

Your groups remind me of something I read years ago. A plot of the surface gravity of the solar system's largest bodies shows steps similar to Bode's Law. Jupiter's (at the cloud tops) is about 2.5 times Earth's. Venus, Saturn, Uranus and Neptune are close to Earth's. Mars and Mercury at 0.38 are about 1 / 2.5 . Divided by 2.5 again is 0.16 which is the moon's surface gravity. Io, Europa, Ganymede, Titan, and Callisto are similar ranging from 0.18 to 0.13.

SFJCody: either I'm looking at the graph the wrong way or you have got Enceladus' density wrong. Your graph suggests slightly above 1 g/cm^3 while recent measurements by Cassini show this to be more around 1.6 g/cm^3. It's much denser than similarly sized Mimas.

Yep, well spotted. Correction made.

http://www.dfw.com/mld/dfw/news/nation/13515853.htm

So, how's about my 1999 suggestion that the cutoff line be a diameter of 2000 km instead? That would allow Pluto to retain its long-established historical membership in the Planet Club, without loosening the membership requirements enough to let all sorts of small riffraff into it.

Reiterating my arm-waving arguement, posted some months back...

Planetisimals, whether rocky or icy, grow by mechanically colliding with the dust and gravel and smaller bodies in their environment.

When the reach a certain size, so that their escape velocity gets to be some number like the average encounter speed with the small stuff they're eating, their "capture cross section area" starts to get to be significantly larger than their physical cross section. This is what I call the vaccuum cleaner effect, due to their gravity.

These protoplanets, no longer planetisimals, now can grow faster than the small stuff, and engage in runaway accretion, cut short by the dissipation of the local nebula, or by gravitational stirring (for example by Jupiter at the asteroid belt) increasing collissional velocities so things are broken up, rather than accreting, in colisions.

My arguement is that a PLANET is an object that had gotten into the gravitationally-enhanced accretion mode, regardless of the absolute diameter involved, for that radius from the sun in the presolar nebula. Pluto, and maybe a few of these other objects really do seem to be off the trend in size-frequency plots in the Kuiper belt, but I'd love to see a best current plot of that, using (1) magnitudes as a standin for real diameters, and (2) diameters, for those bodies that have real numbers rather than albedo dependent estimates.

Bruce:

Anything which makes the Moon a planet is OK by me!

Me, I think a witch is a wooden duck (unless she floats).

Bob Shaw

quoting Elphaba: "I'M MELTING... I'm melting... i'm m......"

Beware of Quantum Ducks: QUARK QUARK!

http://kencroswell.com/TenthPlanetFirstAnniversary.html

Okay, no wonder this committee is having so much difficulty coming to a decision -- they have significant problems with basic arithmetic!

11+8+6 = 19?

I suspect that either the votes for the first proposal are miscounted, since they would create a majority (of 11 out of 19 voters) for that proposal, or there are 25 voters on this committee.

Bill

I think your answer is here

Kuiper Belt Moons Might Be More Common

Summary - (Wed, 18 Jan 2006) Just a few years ago, Pluto was considered unusual for Kuiper Belt Objects because it has a moon. Now three of the four largest KBOs have been discovered with moons, and it's causing astronomers to reconsider how this came about.

Only 11% of smaller KBOs have a moon, and probably captured them with gravity. But the moons for the larger objects likely formed when similarly-sized planetoids collided together, and the debris turned into their moons.

http://www.universetoday.com/am/publish/ku...ns.html?1812006

A planet definition from Alain Maury:
http://www.spaceobs.com/perso/textes/planetsandasteroids.htm

Paper: astro-ph/0601414

Date: Thu, 19 Jan 2006 04:21:30 GMT (55kb)

Title: Exploring the surface properties of Transneptunian Objects and Centaurs
with polarimetric FORS1/VLT observations

Authors: S. Bagnulo, H. Boehnhardt, K. Muinonen, L. Kolokolova, I. Belskaya,
M.A. Barucci

Comments: 11 pages, 7 postscript figures, accepted by A&A
\\
Polarization is a powerful remote-sensing method to investigate solar system
bodies. It is an especially sensitive diagnostic tool to reveal physical
properties of the bodies whose observational characteristics are governed by
small scatterers (dust, regolith surfaces). For these objects, at small phase
angles, a negative polarization is observed, i.e., the electric vector E
oscillates predominantly in the scattering plane, contrary to what is typical
for rather smooth homogeneous surfaces. The behavior of negative polarization
with phase angle depends on the size, composition and packing of the
scatterers. These characteristics can be unveiled by modelling the light
scattering by the dust or regolith in terms of the coherent backscattering
mechanism.

\\ ( http://arXiv.org/abs/astro-ph/0601414 , 55kb)

A planet definition from Parade magazine:

http://www.parade.com/articles/editions/20...ce_Tenth_Planet

That is, no more or less, exactly what Alan has posted here as *his* definition of a planet.

Well, at least they swiped their definition from an authoritative source.

-the other Doug

2003 UB313 is much smaller.

- http://sciencenow.sciencemag.org/cgi/content/full/2006/127/1 - Downsizing the "Tenth Planet"

--- That's surprising, Brown said, because it means that the object reflects a remarkable 92% of the light that hits it--compared with roughly 60% for Pluto. "I had expected it to be darker and considerably larger," Brown said. Geysers may continually coat the surface with fresh frost, he speculated, although how that occurs on such a frigid body is unknown.

However, a chart of 2003 UB313's projected size on Brown's Web site indicates that with a reflectivity of 92%, the object would be roughly 1% larger than Pluto's assumed diameter of 2280 kilometers. The team's previous estimates had ranged from 25% larger (on its Web site) to 50% larger (at NASA's announcement in July). ---

http://www.foothill.fhda.edu/ast/news.htm#Anchor5

Well, this is interesting. I wonder how large the error bars on that figure are? And when is this NASA press conference mentioned in the article going to be held?

Good question! I hate missing Live press conferences!

Astrophysics, abstract
astro-ph/0601654

From: Eugene Chiang [view email]

Date: Fri, 27 Jan 2006 21:49:32 GMT (150kb)

A Brief History of Trans-Neptunian Space

Authors: E. Chiang (UCB), Y. Lithwick (UCB/CITA), R. Murray-Clay (UCB), M. Buie (Lowell), W. Grundy (Lowell), M. Holman (Harvard CfA)

Comments: Refereed, accepted, formatted review chapter for Protostars and Planets V compendium

The Edgeworth-Kuiper belt encodes the dynamical history of the outer solar system. Kuiper belt objects (KBOs) bear witness to coagulation physics, the evolution of planetary orbits, and external perturbations from the solar neighborhood. We critically review the present-day belt's observed properties and the theories designed to explain them. Theories are organized according to a possible time-line of events. In chronological order, epochs described include (1) coagulation of KBOs in a dynamically cold disk, (2) formation of binary KBOs by fragmentary collisions and gravitational captures, (3) stirring of KBOs by Neptune-mass planets (``oligarchs''), (4) eviction of excess oligarchs, (5) continued stirring of KBOs by remaining planets whose orbits circularize by dynamical friction, (6) planetary migration and capture of Resonant KBOs, (7) creation of the inner Oort cloud by passing stars in an open stellar cluster, (8) in situ coagulation of Neptune Trojans, and (9) collisional comminution of the smallest KBOs. Recent work underscores how small, collisional, primordial planetesimals having low velocity dispersion permit the rapid assembly of ~5 Neptune-mass oligarchs at distances of 20-40 AU. We explore the consequences of such a picture. We propose that Neptune-mass planets whose orbits cross into the Kuiper belt for up to ~40 Myr help generate the high-perihelion members of the hot Classical disk and Scattered belt. By contrast, raising perihelia by sweeping secular resonances during Neptune's migration might fill these reservoirs too inefficiently when account is made of how little primordial mass resides in bodies large enough to be observable. These and other frontier issues in trans-Neptunian space are discussed quantitatively.

http://arxiv.org/abs/astro-ph/0601654

New results:

New "planet" is larger than Pluto:

Bonn astronomers measure size of newly discovered solar system object

- http://www.astro.uni-bonn.de/~bertoldi/ub313/

The size measurement of 2003 UB313 is published in the 2 February 2006 issue of Nature. Xena is now 3,000 +/-300 kilometers (Albedo 0.6) wide.



Very interesting:

--- Note on reports of an HST size measurement (31.1.)

Mike Brown gave a public talk recently where he presented some preliminary results on an attempt to measure the size of UB313 with the Hubble Space Telescope [Albedo 0.92 news]. A journalist picked this up and reported it, against Mike Brown's explicit request. In response to this report Mike Brown stated on Jan 31:

"Contrary to rumors otherwise, we're just in the preliminary stages of analyzing the HST data. When we are done we should have a very precise measurement. The study that is coming out in Nature is the best info that we have for now about how big and reflective it is. The uncertainties are large, but it seems a solid result to me. I hope that we will have the HST analysis done within perhaps a month, and I'll be able to say more then." ---

Brown's webpage has an update on progress on deciding whether 2003 UB313 is a planet or not

http://www.newscientistspace.com/article.ns?id=dn8681

You know, planets were being defined and undefined and given names long before the IAU existed. If the IAU insists on sitting on its hands for years and years, I think that astronomers and astronomy-buffs ought to take matters into their own hands and simply adopt a solution. I suspect that the IAU committee have just been thinking too hard about the question. I recommend a solution that required almost no thinking at all :

My solution is:
Our solar system has ten planets; they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto and Proserpina.

The minimal amount of thought that went into it was this:

Pluto has been accepted as a planet for 76 years and that is unlikely to change regardless of what the IAU thinks;
If Pluto is a planet, there is no reason for 2003 UB313 not to be a planet, since it goes around the sun and is bigger than Pluto;
Therefore 2003 UB313 will be accepted as a planet.

I use the name Proserpina, because even though it wouldn't be my first choice for the name, discoverer Mike Brown has favored either Persephone or Proserpina, and Latin forms are preferred for planets.

Edit: I should add that the only way that this represents my private view is that I want to see the nonsense cut through and a decision finally arrived at. I think that this is likely to be what happens at the end of the argument anyway, and I'd rather have it happen immediately than in two, three, or five years' time. I'd be just as happy with a decision that a body has to be at least as big (or as massive) as Mercury in order to be a planet.

Plus you can now say "My Very Educated Mother Just Served Us Nine Pizzas Politely" or Punctually or Pleasantly.

But what happens when we find other KBOs bigger than Pluto and Proserpina, as I am sure we will? Better start using other mythologies besides the Greek:

http://www.pantheon.org/

Astrophysics, abstract
astro-ph/0602316

From: David E. Trilling [view email]

Date: Tue, 14 Feb 2006 19:52:04 GMT (484kb)

The Albedo, Size, and Density of Binary Kuiper Belt Object (47171) 1999 TC36

Authors: J.A. Stansberry, W.M. Grundy, J.L. Margot, D.P. Cruikshank, J. P. Emery, G.H. Rieke, D.E. Trilling

Comments: ApJ, in press (May, 2006)

We measured the system-integrated thermal emission of the binary Kuiper Belt Object 1999 TC36 at wavelengths near 24 and 70 microns using the Spitzer space telescope. We fit these data and the visual magnitude using both the Standard Thermal Model and thermophysical models. We find that the effective diameter of the binary is 405 km, with a range of 350 -- 470 km, and the effective visible geometric albedo for the system is 0.079 with a range of 0.055 -- 0.11. The binary orbit, magnitude contrast between the components, and system mass have been determined from HST data (Margot et al., 2004; 2005a; 2005b). Our effective diameter, combined with that system mass, indicate an average density for the objects of 0.5 g/cm3, with a range 0.3 -- 0.8 g/cm3. This density is low compared to that of materials expected to be abundant in solid bodies in the trans-Neptunian region, requiring 50 -- 75% of the interior of 1999 TC36 be taken up by void space. This conclusion is not greatly affected if 1999 TC36 is ``differentiated'' (in the sense of having either a rocky or just a non-porous core). If the primary is itself a binary, the average density of that (hypothetical) triple system would be in the range 0.4 -- 1.1 g/cm3, with a porosity in the range 15 -- 70%.

http://arxiv.org/abs/astro-ph/0602316