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The Resonant Captures of TNOs

The Resonant Captures of TNOs. Ing-Guey Jiang (NCU, Taiwan) Li-Chin Yeh (NHCUE, Taiwan). Outline. The Resonances The Resonant TNOs 3. Review of Previous Work 4. The Model 5. The Results 6. Conclusions. The Resonances. GJ 876 and HD 82943 are in 2:1 Resonance

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The Resonant Captures of TNOs

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  1. The Resonant Captures of TNOs Ing-Guey Jiang (NCU, Taiwan) Li-Chin Yeh (NHCUE, Taiwan)

  2. Outline • The Resonances • The Resonant TNOs 3. Review of Previous Work 4. The Model 5. The Results 6. Conclusions

  3. The Resonances • GJ 876 and HD 82943 are in 2:1 Resonance • 47 UMa is close to 7:3 Resonance • 55 Cancri are confirmed to be in 3:1 Resonance • Kirkwood Gaps in Asteroid Belt • What mechanism make them in resonance ? • Are these systems dynamically stable ?

  4. The Resonant Trans Neptunian Objects • Also called “Plutinoes” • They are in 3:2 mean motion resonance with the Neptune • They are about 1/3 of whole TNO population • There are only seveal TNOs in 2:1 resonance

  5. Malhotra (1995) • Possible migrations suggested by Fernandez & Ip (1984) • Assuming pure radial migration • The Neptune was migrating outward • Its mean motion resonance is swept ahead through the Kuiper Belt and captures Pluto along with plutinoes into 3:2 resonance • This theory predicted the populations of the 3:2 and 2:1 resonances to be the same order • Zhou et al. (2002)’s stochastic migration

  6. The Migrating Orbit • Pure radial migration is too naïve • Eccentricity should increase (Yeh and Jiang 2001) • Neptune is currently on a circular orbit • Thommes et al. (1999) showed that one needs a massive Kuiper Belt to circularize the Neptune’s orbit

  7. The Mass of Kuiper Belt • There is an observational upper limit, about 0.1 Earth mass • If it was more massive, it has to be depleted • Levison and Morbidelli (2003) proposed a pushing-out model but only have 2:1 TNOs • Could Neptune form around current positions ? Bryden et al. (2000) claimed “Yes”

  8. The Drag-Induced Resonant Capture • The TNOs shall be forming while the proto-stellar disc is there • It influences the proto-TNOs • TNOs are losing energy due to Drag • Drag might make the TNOs migrate inward • Could these TNOs get captured into resonance by the Neptune ? • Into 3:2 or 2:1 ?

  9. Jiang & Yeh (2004) • A system of the Sun-Neptune-Disc and test particles • The disc mass is 0.01 Solar Mass, giving both gravitational force and drag • 900 test particles are randomly placed in the region around 30 to 60 AU from the Sun • The simulation lasts about 10^7 years • Calculating both 3:2 and 2:1 Resonant Arguments • Neptune already on circular orbit, no matter where it was formed

  10. The Results • Particles migrate inward due to drag • Number of particles captured into 3:2 resonance steadily increases with time • Great fraction of particles are captured into 3:2 resonance by the end of simulation • None is captured into 2:1 resonance • However, only one drag strength is studied • The nature of test particles is not assigned

  11. The Recent Work • Try different drag strength • Test particles represent km-sized planetesimals • Still more captured into 3:2 but the ratio of particles captured into 3:2 over the ones in 2:1 depends on the drag strength, i.e. migrating speed • We will consider the capture of dust grains

  12. Conclusions • Disc’ drag reduces particles’ energy and make them migrate inward • We can produce 3:2 resonant TNOs easily and thus seem to be an attractive mechanism • The main problem: Was drag strong enough ? • Youdin & Chiang (2004) shows that a model with MNSN will have enough drag to make grains migrate inward • The main concern of Neptune’s outward migration: it cannot be a purely radial migration, it could be complicated • Combinations with 2 possibilities is an interesting work

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