Planet Formation in a disk with a Dead Zone

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Planet Formation in a disk with a Dead Zone

• Soko Matsumura (Northwestern University)
• Ralph Pudritz (McMaster University)
• Edward Thommes (Northwestern University)

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Outline

• Evolution of the Dead Zones
• Planet Formation
• Reproduce the standard models
• What happens with a dead zone?
• Summary

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Planet formation and migration in an evolving
disk with a dead zone

• Pollack et al. (1996), Hubickyj et al. (2005)
  giant planet formation at a fixed orbital radius
  ( 5.2 AU) with no disk evolution
• Alibert et al. (2005) studied giant planet
  formation with migration and disk evolution, and
  found that planet migration can speed up the
  formation.
• Jupiter can be made within about 106 years.
• Planet migration has to be at least 10 times
  slower.
• One of the problems of the core accretion
  scenario planet migration seems to be too fast.

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Motivation

• One of the problems of the core accretion
  scenario planet migration seems to be too fast.
• Alibert et al. (2005) studied giant planet
  formation with migration and disk evolution, and
  found that planet migration can speed up the
  formation.
• Jupiter can be made within about 106 years.
• Planet migration has to be at least 10 times
  slower.

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Planet formation and migration in an evolving
disk with a dead zone

• If a planet is made outside the dead zone, we may
  not need to artificially slow down the planet
  migration.

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Evolution of Dead Zones

• There is a critical surface mass density below
  which the MRI becomes active.
• Cosmic ray attenuation length 100 g cm-2
• In our fiducial model Scrit 16 g cm-2
• Gammie (1996) Mass accretion through the surface
  layers can explain the mass accretion rate onto
  the central star.

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Evolution of Dead Zones

• Gammie (1996) Mass accretion through the surface
  layers can explain the observed mass accretion
  rate onto the central star.

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Evolution of Dead Zones

• Gammie (1996) Mass accretion through the surface
  layers can explain the mass accretion rate onto
  the central star.
• There is a critical surface mass density below
  which the MRI becomes active.
• Cosmic ray attenuation length 100 g cm-2
• In our fiducial model Scrit 16 g cm-2

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Evolution of Dead Zones

• There is a critical surface mass density below
  which the MRI becomes active.
• Cosmic ray attenuation length 100 g cm-2
• In our fiducial model Scrit 16 g cm-2
• Gammie (1996) Mass accretion through the surface
  layers can explain the mass accretion rate onto
  the central star.
• Turner et al. (2006) Gas in the dead zone
  accretes toward the star only slightly slower
  than that in the surface layers.

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Evolution of Dead Zones

• Averaged viscosity alpha

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Evolution of Dead Zones

• Averaged viscosity

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Evolution of Dead Zones

• Averaged viscosity

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Evolution of Dead Zones
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Evolution of Dead Zones
Mdisk 0.01 Msolar
107 yrs
106 yrs
105 yrs
104 yrs
Mdisklt MJ
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Planet Formation (core accretion scenario)

• Core accretion Gas accretion

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Planet Formation (core accretion scenario)

• Core accretion Gas accretion

• Pollack et al. (1996) in-situ planet formation
• Planetary core of 0.6 ME

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Planet Formation (core accretion scenario)

• Core accretion
• Rapid core growth upto 10-3 - 10-2 ME (Ida
  Makino 1993)
• Oligarchic growth (e.g. Kokubo Ida 1998,
  Thommes et al. 2003)
• Gas accretion
• Scaled with Kelvin-Helmholtz timescale (e.g.
  Pollack et al. 1996, Ikoma et al. 2000, Bryden et
  al. 2000, Ida Lin 2004)

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Planet Formation (core accretion scenario)

• Core accretion
• Rapid core growth upto 10-3 - 10-2 ME (Ida
  Makino 1993)
• Oligarchic growth (e.g. Kokubo Ida 1998,
  Thommes et al. 2003)
• Gas accretion
• Scaled with Kelvin-Helmholtz timescale (e.g.
  Pollack et al. 1996, Ikoma et al. 2000, Bryden et
  al. 2000, Ida Lin 2004)

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Planet Formation (core accretion scenario)

• Wide-range in gas accretion timescale

Bryden et al. (2000) Pollack et al.
(1996) Ikoma et al. (2000) Ikoma et al. (2000)
core accretion is stopped Ida Lin
(2004) Chambers (2007) Dashed lines include the
effect of lowered opacity
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Planet Formation (core accretion scenario)

• Pollack et al. (1996) Jupiter can be made within
  8 x 106 years at 5.2 AU.
• Use the solid surface mass density
• Ss 300(r/AU)-2 g cm-2
• and a planetesimal size (10km).
• Oligarchic growth is slower than runaway growth.

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Planet Formation (core accretion scenario)

• Lower opacity speeds up gas accretion (e.g. Ikoma
  et al. 2000, Hubickyj et al. 2005).
• Hubickyj et al. (2005) Jupiter can be made
  within a few 106 years.
• Use a fixed opacity of 0.03 cm2 g-1.

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Planet Formation in a disk with a dead zone

• Initial disk mass is Md 0.01
  Msolar and disk temperature is calculated as in
  Chiang et al. (2001).
• Dead zone is initially stretched out to 13 AU.
• Planetary core with 0.6 ME is placed at 10 AU.
• Standard opacity (1 cm2 g-1) assumed.

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Planet Formation in a disk with a dead zone
Decreased opacity (0.03 cm2 g-1)
Standard opacity (1 cm2 g-1)
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Planet Formation in a disk with a dead zone
Standard opacity (1 cm2 g-1)
Decreased opacity (0.03 cm2 g-1)
Core
Total
Envelope
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Planet Formation in a disk with a dead zone

• Planetary core with 0.6 ME is placed at 15 AU.
• Core accretion is truncated at 10 ME.
• Standard opacity is assumed.

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Planet Formation in a disk with a dead zone
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Planet Formation in a disk with a dead zone

• Formation with a dead zone takes about 8x106
  years.

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Planet Formation (core accretion scenario)

• Is there an optimized place to form planets?

Ikoma et al. (2000)
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Summary

• Dead zones evolve rapidly.
• From 13 AU to 1 AU within 2 x 106 years.
• Dead zones help planet formation by slowing down
  the migration.
• Core mass as well as the difference in
  viscosities between active and dead zones may
  affect the evolution of a planet.