Structure and evolution of large kuiper belt objects and dwarf planets
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Structure and Evolution of Large Kuiper Belt Objects and Dwarf Planets. William B. McKinnon 1 , S. Alan Stern 2 , E. Asphaug 3 1 Dept. EPSC and McDonnell Center for the Space Sci.,Washington Univ., St. Louis, MO USA 2 Southwest Research Inst., Boulder, CO USA 3 UC Santa Cruz, CA USA

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Structure and evolution of large kuiper belt objects and dwarf planets

Structure and Evolution of Large Kuiper Belt Objects and Dwarf Planets

William B. McKinnon1, S. Alan Stern2, E. Asphaug3

1Dept. EPSC and McDonnell Center for the Space Sci.,Washington Univ., St. Louis, MO USA

2Southwest Research Inst., Boulder, CO USA

3UC Santa Cruz, CA USA

TNO 2006, Catania, 5 July 2006


r min

r max

Stern, McKinnon & Lunine 1997

Jewitt & Sheppard 2002

Axial ratio ≥ 1.5:1:0.7 –>

1090 kg/m3 ≤ r ≤ 1270 kg/m3

The nature of the beast…


r min

r max

  • ≤ 1270 kg/m3

    740

    530

    375

Sheppard & Jewitt 2002


Stansberry et al. 2006

1999 TC36

1998 SM165 Spencer et al., this meeting

Dprimary ≈ 250–330 km; r = 0.35 –0.85 g cm-3

porosity

vs.

solid density


Porosity

R

r

  • Real geological rubble, regoliths have f ≈ 0.4

  • Cometary porosities (f ≥ 0.5) are possible ... for comets!

Carrier et al. 1991

Porosity

  • Pressures in large KBOs (r ≥ 100 km) non-negigible:

  • Pc = 30 MPa for spherical Varuna of ice density

  • Real geological rubble, regoliths have f ≈ 0.4

  • Cometary porosities (f ≥ 0.5) are possible ... for comets!


Phydro

Durham, McKinnon & Stern, 2005






Radius (km)

rrock = 2.63 g cm-3

ACM 2005



2003 EL61

1999 TC36

Brown, Rabinowitz and coworkers

Yes, Gerard,

there is a

Santa KBO…



Discussion

  • Range of believable densities outside the Pluto/Triton + porosity paradigm

  • Moderate to large KBOs have a range of densities/compositions-- classes?

  • Asteroid compositional classes – S, M, C, P, D, etc due to different factors:

Distance from Sun --> ice content

Internal differentiation and collisional evolution

  • Large ice-rich and rock-rich KBOs require strong collisional evolution

  • Pluto and EL61 imply different collisional environments

  • More constraints on formation models (Viva Niza!)

  • Much more to come on internal evolution of big KBOs!


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