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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. 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

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  1. 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

  2. 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…

  3. r min r max • ≤ 1270 kg/m3 740 530 375 Sheppard & Jewitt 2002

  4. 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

  5. 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!

  6. Phydro Durham, McKinnon & Stern, 2005

  7. Ice Compaction DMS2005

  8. EOS Comparison

  9. ACM 2005

  10. ACM 2005

  11. Radius (km) rrock = 2.63 g cm-3 ACM 2005

  12. Phoebe Thermal Evolution

  13. 2003 EL61 1999 TC36 Brown, Rabinowitz and coworkers Yes, Gerard, there is a Santa KBO…

  14. 1999 TC36

  15. 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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