DDA 2015 – Using Populations of Gas Giants to Probe the Dynamics of Planet Formation

This is one of a series of notes taken during the 2015 meeting of the AAS Division on Dynamical Astronomy, 3-7 May, at CalTech. An index to this series (all the papers presentedĀ at the meeting) is here.

Session: Exoplanet Theory I

Ruth Murray-Clay (UC Santa Barbara) (invited)




  • How do giant planets and brown dwarfs form?
  • Architecture of Solar System is atypical.
  • Lots of gas giants at large distances, small distances (“hot Jupiters”), but not much in between a la Solar System. Why?
  • SS: rocky planets (~1 AU), gas giants (~5-10 AU), ice giants (~20-30 AU)
  • Theory: cannot predict numbers, but can predict patters in system architectures and statistical populations
  • How to get companions to stars: 1) turbulent fragmentation, 2) grav. instability, 3) core accretion
  • HR8799: testbed for planet formation theories
    • 4 Jupiter-mass planets
    • turbulent frag.? No: system is not hierarchichal
    • grav. inst.?
      • iffy – minimum fragment distance problems (but could have migrated)
      • Timing – collapse must occur at end of infall or a binary star results
    • core accretion?
      • dynamical (growth) timescale is too long ($t_{grow} > t_{infall}$)
      • $t_{grow} > t_{disk}$
      • cross section regimes — all problematic:
        • physical cross section
        • grav focusing
        • gas drag capture
  • Make gas useful.
    • no gas: particles can orbit inside core Hill radius
    • gas: “wind shear”
      • binary capture
      • particle capture can occur out to Hill radius
      • growth time at 70 AU can be short enough to nucleate an atmosphere
      • turbulent gas: okay
    • accretion cross sections increase by up to $10^4$
  • Gemini Planet Imager couldĀ confirm this theory.
  • Metal-rich stars hostmorehotJupiters and highly eccentric planets: signature of planet-planet interactions? Why?
    • Scattering?
    • Secular chaos?
    • Perhaps those systems form many Jupiters.
  • Are the solar system analogs orbiting low metallicity stars?

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