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

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

5. KBO Workshop, 9/1/2003 Science 292, 1334 (2001)

6. KBO Workshop, 9/1/2003

7. 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

8. KBO Workshop, 9/1/2003 Comet Taxonomy

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

10. KBO Workshop, 9/1/2003 Comet with a = 1000 AU has 50% chance of ejection in one passage Duncan, Quinn, and Tremaine (1987)

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

12. KBO Workshop, 9/1/2003 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. Fading Problem

13. KBO Workshop, 9/1/2003 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 a 0 between 4 and 40 AU –Cold: 2000 particles, root-mean-square e 0 = 0.02, i 0 = 0.01 –Warm: 1000 particles, root-mean-square e 0 = 0.2, i 0 = 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

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19. Duncan, Quinn, Tremaine (1987)

20. KBO Workshop, 9/1/2003

21. Dybczynski 2002

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25. Duncan, Quinn & Tremaine (1987)

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

27. KBO Workshop, 9/1/2003 Mass of the Oort Cloud  Outer Oort cloud: 0.5 x 10 12 comets with absolute magnitude H 10 < 11 with absolute magnitude H 10 < 11  Number in inner Oort cloud ~ Number in outer Oort cloud  Total of 10 12 comets in the entire Oort cloud Total of 10 12 comets in the entire Oort cloud  Calibrate to Halley, which has H 10 ~ 6 and known size, assume density of 0.6 g cm -3 and Everhart’s size distribution  mean mass of a comet ~ 4 x 10 16 g = 7 x 10 -12 Earth masses mean mass of a comet ~ 4 x 10 16 g = 7 x 10 -12 Earth masses  Present-day mass of Oort cloud M now ~ 7 Earth masses  Fraction of comets in the Oort cloud at present:  0.046  Original mass in planetesimals between 4 and 40 AU: M disk  M now/  ~ 150 Earth masses M disk  M now/  ~ 150 Earth masses

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

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32. Science 280, 1250 (1998)

33. KBO Workshop, 9/1/2003 Garcia-Sanchez et al., Astron. J. 117, 1042 (1999) 0.4»0.6 M_0.4»0.6 M_ Gliese 710 M ~ 0.5 M Sun p ~ 70,000 AU

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35. 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

36. KBO Workshop, 9/1/2003 Newton, PASP 6, 30 (1894)

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38. Tozzi and Licandro, Icarus 157, 187 (2002)

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

40. KBO Workshop, 9/1/2003 Levison et al., Science 296, 2212 (2002)

41. KBO Workshop, 9/1/2003 Dybczynski 2002

42. KBO Workshop, 9/1/2003 Oort Cloud “To Do” List 1.Assume the Sun formed in a cluster 2.Let planets grow and migrate 3.Include other perturbers:  planet or brown dwarf in the Oort cloud  molecular clouds  residual gas in solar nebula 4.Model collisions 5.Include fading on the way out

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

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

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

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47. Nature 409, 589 (2001)

48. KBO Workshop, 9/1/2003 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.