2004 DW -- Largest TNO?

[selden]

Gee. The planetary specialists here are falling down on the job!

2004 DW was discovered a few days ago (and already mentioned by CNN). With an estimated diameter of 1600km, it's larger than Quaoar.

Code: Select all

"2004 DW" "Sol"
{
   Class "asteroid"
   Mesh   "roughsphere.cms"
   Texture "asteroid.jpg"
   # the same color as Eros
   Color   [ 0.52 0.47 0.42 ]
   BlendTexture true
   Radius  800
   Albedo 0.12 #? guestimated to be the same as Quaoar's

   InfoURL "http://www.gps.caltech.edu/~chad/2004dw/"

   EllipticalOrbit
   {
      Period             248.0
      SemiMajorAxis     39.4739612
      Eccentricity       0.2179056
      Inclination       20.55527
      AscendingNode    268.53704
      ArgOfPericenter   73.33446
                   MeanAnomaly      157.53750
      Epoch  2453200.5
     
   }
}


[TERRIER]

Excellent, I shall paste this code into my 'kuiperbelt.ssc' that already contains Quaoar, and maybe use the Quaoar texture.

regards
TERRIER

[JackHiggins]

Great! I was going to post about this on the Physics/Astronomy forum (no, really I was!) but I didn't think the size had been pretty much confirmed yet.

[selden]

Jack,

My impression is that there are still pretty big error bars on the size estimate, but since they mention the possibility of a 1600km diameter, that's what I put in the SSC file. Even the orbit is still not known as precisely as they'd like. But give them time: they've only known about it for a few days!

I got the orbital parameters from Minor Planets Electronic Circular 2004-D15.

[granthutchison]

Selden:
I'm just wondering if this might not be more accurately portrayed as a smooth sphere. At 800km radius it's comparable to Rhea, Oberon and Titania, and considerably larger than Miranda, Ariel, Umbriel, Tethys, Dione, Iapetus and Charon. It's only in the radius range 200-300km that we begin to see a mix of spherical objects (Mimas, Enceladus) and lumpy objects (Proteus).
Admittedly we don't know the structure of Edgeworth-Kuiper objects in detail, but it seems like our known sample of cold icy objects are all quite spherical by the time this radius is reached.

Grant

[selden]

Grant,

I believe you're right.

One estimate I've seen is that silicate objects with a mass > 3x10^21 kg have to be round.
http://www.gravityfromthegroundup.org/pdf/roundbodies.pdf

Presumably KBOs don't have the structural strength of silica, so smaller masses will be round.

Assuming an average mass of 1g/cm^3 (water), an object with a radius of 800km would have a volume of 4piR^3 = 12.5x(8x10^7cm)^3 = 6.4x10^24 cm^3. i.e. a mass of 6.4x10^21 kg. So it probably is as round as a billiard ball, unless I've slipped a decimal point somewhere.