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Report from the Oort Cloud

Report from the Oort Cloud. Simulations of the Formation of the Comet Reservoir Luke Dones Hal Levison Paul Weissman Martin Duncan. Scenario for Oort Cloud Formation. Icy planetesimals formed in the region of the giant planets

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Report from the Oort Cloud

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  1. Report from the Oort Cloud Simulations of the Formation of the Comet Reservoir Luke Dones Hal Levison Paul Weissman Martin Duncan

  2. KBO Workshop, 9/1/2003

  3. Scenario for Oort Cloud Formation Icy planetesimals formed in the region of the giant planets Some formed the cores of Jupiter, Saturn, Uranus, and Neptune Some stayed small and were scattered into big orbits Most were ejected from the Solar System, but the orbits of some were lifted from the planetary region by galactic tides and passing stars and reached the Oort Cloud This scenario neglects gas, interactions between planetesimals due to gravity or collisions, … Tides and stars perturb some comets back into orbits that approach the Sun within a few AU, making them sublime KBO Workshop, 9/1/2003

  4. Tremaine, in Planets Around Pulsars (1993) KBO Workshop, 9/1/2003

  5. Goals To determine … • where Oort cloud [OC] comets originated (Conventional wisdom: Uranus-Neptune region, but compositions are diverse) • the fraction of comets that end up in the Oort cloud  the original mass in solids in the giant planets region • the spatial distribution of comets in the OC • Does a massive inner OC exist?  If so, big comet showers are possible • the temperatures reached by OC comets as their orbits evolved KBO Workshop, 9/1/2003

  6. 200,000 AU Comets ejected Outer Oort Cloud 20,000 2000 Long period comets 50 5 Inner Oort cloud Kuiper Belt, scattered disk KBO Workshop, 9/1/2003

  7. Wiegert and Tremaine (1999) KBO Workshop, 9/1/2003

  8. Fading Problem • Observed • 109 new long-period comets (a > 10,000 AU) • 178 returning long-period comets (34 AU < a < 10,000 AU)  • There are 1.6 returning comets for each new comet. • Predicted • 57 returning comets for each new comet (gambler’s ruin model) • 34 returning comets for each new comet (Paul Wiegert’s thesis) •  We’re still off by a factor of 20. KBO Workshop, 9/1/2003

  9. Calculations Direct integrations of 3000 “comets” for up to 4 billion years Integrations include Sun Jupiter, Saturn, Uranus, Neptune with current masses and orbits Present-day Galactic tides (r and z components) Passing stars Two sets of runs, both with a0 between 4 and 40 AU Cold: 2000 particles, root-mean-square e0 = 0.02, i0 = 0.01 Warm: 1000 particles, root-mean-square e0 = 0.2, i0 = 0.1 Integrate orbit of each comet until it: is ejected from the Solar System impacts the Sun or a planet survives for 4 billion years KBO Workshop, 9/1/2003

  10. KBO Workshop, 9/1/2003

  11. KBO Workshop, 9/1/2003

  12. KBO Workshop, 9/1/2003

  13. KBO Workshop, 9/1/2003

  14. KBO Workshop, 9/1/2003

  15. Duncan, Quinn, Tremaine (1987) KBO Workshop, 9/1/2003

  16. KBO Workshop, 9/1/2003

  17. KBO Workshop, 9/1/2003

  18. KBO Workshop, 9/1/2003

  19. Hale-Bopp Halley KBO Workshop, 9/1/2003 Everhart, Astron. J.72, 1002 (1967)

  20. Mass of the Oort Cloud • Outer Oort cloud: 0.5 x 1012 comets with absolute magnitude H10 < 11 • Number in inner Oort cloud ~ Number in outer Oort cloud  Total of 1012 comets in the entire Oort cloud • Calibrate to Halley, which has H10 ~ 6 and known size, assume density of 0.6 g cm-3 and Everhart’s size distribution  mean mass of a comet ~ 4 x 1016g = 7 x 10-12Earth masses •  Present-day mass of Oort cloud Mnow~ 7 Earth masses • Fraction of comets in the Oort cloud at present: h = 0.046 •  Original mass in planetesimals between 4 and 40 AU: Mdisk= Mnow/h~ 150 Earth masses KBO Workshop, 9/1/2003

  21. Hahn & Malhotra (1999) KBO Workshop, 9/1/2003

  22. KBO Workshop, 9/1/2003

  23. KBO Workshop, 9/1/2003

  24. KBO Workshop, 9/1/2003

  25. Science 280, 1250 (1998) KBO Workshop, 9/1/2003

  26. KBO Workshop, 9/1/2003

  27. Cometary Impact Rates • Impact rates on Earth and galilean satellites due to active long-period comets are low at present (Zahnle et al. 1998) • Two uncertainties: • Inner Oort cloud: Many or few comets? • “Fading” My my, hey hey, Rock and roll is here to stay It's better to burn out, than to fade away My my, hey hey KBO Workshop, 9/1/2003

  28. KBO Workshop, 9/1/2003

  29. 57P/du Toit-Neujmin-Delporte KBO Workshop, 9/1/2003

  30. Levison et al., Science296, 2212 (2002) KBO Workshop, 9/1/2003

  31. Oort Cloud “To Do” List • Assume the Sun formed in a cluster • Let planets grow and migrate • Include other perturbers: • planet or brown dwarf in the Oort cloud • molecular clouds • residual gas in solar nebula • Model collisions • Include fading on the way out KBO Workshop, 9/1/2003

  32. Icarus 150, 151–162 2001) ° Adams and Laughlin, Icarus 150, 151 (2001) KBO Workshop, 9/1/2003

  33. Ida et al.,Ap. J.528, 351 (2000) KBO Workshop, 9/1/2003

  34. First 50 Myr First 5 Myr Thommes et al., Astron. J.123, 2862 (2002) KBO Workshop, 9/1/2003

  35. KBO Workshop, 9/1/2003

  36. KBO Workshop, 9/1/2003 Nature 409, 589 (2001)

  37. Conclusions • The fraction of comets that reach the Oort cloud and survive to the present is small, < 5%. • Efficiency is low because most comets evolve inward and are ejected from the Solar System by Jupiter or Saturn. • Two-stage formation: • Early by Jupiter and Saturn • Late by Uranus and Neptune (peaks at 1 billion years) • Typical comet evolves inward to ~10 AU (Saturn’s distance from Sun) before being placed in the Oort cloud. • Inner Oort cloud does not appear to be the Phantom Menace • More observations and modeling are needed to work out the cosmogonic implications. KBO Workshop, 9/1/2003

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