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Assessing the Threat of Oort Cloud Comet Showers

Explore simulation results and calculations on the probability and frequency of comet showers reaching the inner solar system from the Oort Cloud. Understand the impact of stellar encounters on the shower strength and intensity. Findings shed light on the dynamics of long-period comets in our cosmic neighborhood.

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Assessing the Threat of Oort Cloud Comet Showers

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  1. Assessing the Threat of Oort Cloud Comet Showers Nathan Kaib & Tom Quinn University of Washington

  2. Outline Long-Period Comet Production Jupiter-Saturn Barrier Simulation Results Comet Shower Probability

  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. 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

  7. Simulations • Initial cloud orbits (~106) drawn from recent OC formation simulation results (Kaib & Quinn, accepted) • Modify SWIFT (Levison & Duncan, 1994) with time-reversible adaptive timestepping routine (Kaib & Quinn, accepted) • Evolved under influence of Sun, 4 giant planets, Milky Way tide and passing stars • Vary stellar mass, impact parameter, and encounter velocity

  8. 25,000 AU 4 AU M* = MSun v = 20 km/s, Dmin = 3000 AU Dt = 105 yrs

  9. Calculate years for normal LPC flux to produce comets Quantifying Shower Strength M* = 0.8 MSun v = 20 km/s Dmin = 1300 AU LPC defined as q < 5 AU

  10. Simulation Results v = 20 km/s

  11. Use impulse approximation to calculate DvSun for each stellar passage: DvSun = (2GM*)/(bv)

  12. One parameter controls shower strength

  13. Finding Shower Frequency • Use Rickman et al. (accepted) stellar encounter code to generate ~106 passages • Find dN(DvSun)/dt

  14. 1/t ~ (DvSun)-2(Rickman et al., accepted)

  15. Conclusions • Comet shower intensity for a given Oort Cloud is basically governed by one parameter: DvSun • Showers releasing at least 10 Myrs of LPCs occur every 100 Myrs • Showers releasing at least 40 Myrs occur every Gyr

  16. Conclusions II • Transforming results to an impact rate is HARD: Need to know real current flux of LPCs • Weissman (2007) estimates 1 background LPC impact every 38 Myrs • Implies 1 shower-induced impact every Gyr • Implies showers not a significant additional impactor source • Conservative estimate: we use a minimum inner Oort Cloud population

  17. Divide LPC distribution by Oort Cloud distribution  Probability of LPC as a function of a

  18. Regions Sampled by LPCs

  19. Effects of Solar Formation Setting Inner Oort Cloud population very sensitive to formation environment of Sun (Fernadez & Brunini, 2000; Brasser et al., 2006; Kaib & Quinn, accepted)

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