Evaluating the Effects of Oort Cloud Comet Showers on the Earth Nathan Kaib University of Washington

Background Halo of km-size bodies surrounding solar system Comprised of icy planetesimals leftover from planet formation Scattered out by encounters with giant planets Reservoir of Long-Period Comets

Oort Cloud extends out to ~200,000 AU

Long-Period Comets

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Jupiter Barrier Comets must have large perihelion shift to make it past Jupiter in one orbital period Only weakly bound comets will have large perihelion changes Jupiter shields inner solar system from inner 20,000 AU of Oort Cloud 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 AU

Inner Oort Cloud Strength of shower depends on: –Stellar encounter –Population of Inner Oort Cloud Inner Oort Cloud population very sensitive to Sun’s birthplace environment No Cluster30 stars/pc stars/pc 3 (Kaib & Quinn, submitted)

Shower Simulations Each simulation contains ~10 6 comets These are run for 40 Myrs and include one very close stellar passage, many weaker encounters and galactic tide Formation environment and stellar encounter parameters are varied Flux of objects coming into the inner 5 AU is monitored

Results Encounter: 1 M Sun, 3000 AU, 10 km/s No Cluster 30 stars/pc 3

Conclusions Close stellar passages can raise the long-period comet flux by a factor of for 10 5 years To assess affect on Earth we need better measurement of LPC size distribution and current LPC flux New generation surveys (LSST, Pan-STARRS) will better determine the background flux in the coming years