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Using Known Long-Period Comets to Constrain the Inner Oort Cloud and Comet Shower Bombardment

Using Known Long-Period Comets to Constrain the Inner Oort Cloud and Comet Shower Bombardment. Nathan Kaib & Tom Quinn University of Washington. Outline. Long-Period Comet Production Inner Oort Cloud Comet Production Constraints from Known LPCs Comet Shower Significance. Long-Period Comets.

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Using Known Long-Period Comets to Constrain the Inner Oort Cloud and Comet Shower Bombardment

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  1. Using Known Long-Period Comets to Constrain the Inner Oort Cloud and Comet Shower Bombardment Nathan Kaib & Tom Quinn University of Washington

  2. Outline Long-Period Comet Production Inner Oort Cloud Comet Production Constraints from Known LPCs Comet Shower Significance

  3. Long-Period Comets

  4. X

  5. 25000 AU Jupiter-Saturn Barrier • Comets must have large perihelion shift to make it past Jupiter/Saturn in one orbital period • Only weakly bound comets will have large perihelion changes • Jupiter/Saturn shield inner solar system from inner 20,000 AU of Oort Cloud

  6. Simulations • Initial cloud orbits (~106) drawn from recent OC formation simulation results (Kaib & Quinn, 2008) • Oort Cloud model has 1.5:1 inner-to-outer population ratio • Modify SWIFT (Levison & Duncan, 1994) with time-reversible adaptive timestepping routine (Kaib & Quinn, 2008) • Evolved under influence of Sun, 4 giant planets, Milky Way tide and passing stars for 1.2 Gyrs • Analyze LPCs from last 200 Myrs

  7. Start OC Objects Fates a = 500,000 AU Start Constrained a (AU) x Unconstrained NOC

  8. Inner OC LPCs q = 1 AU a = 28,000 AU Start Similar evolution in SDO simulations (Levison et al., 2006)

  9. Inner OC LPCs Constrained a (AU) Unconstrained NOC

  10. Original Orbits qLPC < 5 AU

  11. Incoming Orbits qLPC < 5 AU

  12. Inner OC LPCs a (AU) Start NOC

  13. Population Constraints • Predicted LPC rate: 1/116,000 per Myr • Max Observed rate: 10 per yr (everhart, 1967) • Predicted population: ~1012 km-sized bodies between 3,000 and 20,000 AU (assuming nOC ~ r -3.2) • Not much larger than current outer Oort Cloud population estimates (3-5 x 1011) • Modest inner Oort Cloud can produce observed LPC flux

  14. 25000 AU Comet Showers • Rare close stellar encounters (< 5000 AU) are able to perturb more tightly bound orbits • The Earth is temporarily exposed to the entire Oort Cloud • Possible source of mass extinctions seen in fossil record (Hut et al., 1987; Farley et al., 1998)

  15. Comet Shower LPCs a (AU) NOC

  16. 25,000 AU 4 AU M* = MSun v = 20 km/s, Dmin = 3000 AU Dt = 105 yrs

  17. Relative Shower Strength DvSun = (2GM*)/(bv)

  18. 1.5:1 3:1 10:1 Relative Shower Strength 1/t ~ (DvSun)-2(Rickman, 2008)

  19. Constrained Shower Curve (Weissman, 2007) most powerful showeryields 2-3 km-sized impactors

  20. 3 impacts 2 Myr He3 spike (Farley et al., 1998) Rohde & Muller (2005)

  21. Conclusions • Inner Oort Cloud is a significant and perhaps dominant source of LPCs • Current LPC flux gives an estimate of the total Oort Cloud population, not just outer • Implies comet showers are not responsible for more than ~1 extinction event

  22. Oort Cloud Mass Problem • Outer Oort Cloud traps 1-2% of planetesimals during formation • Previous outer Oort Cloud mass estimates implied > 200 MEarth planetesimal disk between 4 and 40 AU (Dones et al., 2004) • Inner Oort Cloud can trap more efficiently (5-15%) and still produce observed LPCs (Brasser et al., 2006; Kaib & Quinn, 2008)

  23. Disk Mass Requirements Minimum mass solar nebula  40 MEarth(Dones et al., 2004)

  24. LPC Inclinations 55% Retrograde

  25. LPC semimajor axes Inner amed = 26,000 AU; Outer amed = 35,000 AU Observed amed = 27,000 AU

  26. Compact Inner Clouds (Brasser et al., 2006) ~103 MSun/pc3 produces Sedna and LPCs

  27. Showers from Alternative Clouds A < 3,000 AU case requires 1200 MEarth disk

  28. Quantifying Shower Strength M* = 0.8 MSun v = 20 km/s Dmin = 1300 AU LPC defined as q < 5 AU

  29. Jupiter-Saturn Barrier Edge log D(1/a) q (AU) Duncan et al. (1987)

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