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

X

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

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

25000 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 Cluster 30 stars/pc3 100 stars/pc3

(Kaib & Quinn, submitted)

Shower Simulations

• Each simulation contains ~106 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 MSun, 3000 AU, 10 km/s

No Cluster

30 stars/pc3

Conclusions• Close stellar passages can raise the long-period

comet flux by a factor of 200-400 for 105 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