giant planet accretion and migration : surviving the type i regime edward thommes norm murray cita,...
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Giant Planet Accretion and Migration:
Surviving the Type I Regime
Giant Planet Accretion and Migration:
Surviving the Type I Regime
Edward Thommes
Norm Murray
CITA, University of Toronto
Edward Thommes
Norm Murray
CITA, University of Toronto
The Western Workshop, UWO, May 19, 2006The Western Workshop, UWO, May 19, 2006JPL
Gas giant formation: The core accretion model
Gas giant formation: The core accretion model
Gas disk lifetime sets upper limit on gas giant formation: ~1-10 Myrs from observations (e.g. Haisch, Lada & Lada 2001)
The core accretion model (Mizuno 1980, Pollack et al 1996):
1. Solid core grows, ~10 MEarth
2. Core accretes massive gas envelope, 100+ MEarth
Observational support for core accretion: planet-metallicity correlation
(Gonzalez 1997, Fischer & Valenti 2003)
HD 149026 planet (Saturn mass, ~70 MEarth core; Sato et al. 2005, Charbonneau et al 2006)
Gas disk lifetime sets upper limit on gas giant formation: ~1-10 Myrs from observations (e.g. Haisch, Lada & Lada 2001)
The core accretion model (Mizuno 1980, Pollack et al 1996):
1. Solid core grows, ~10 MEarth
2. Core accretes massive gas envelope, 100+ MEarth
Observational support for core accretion: planet-metallicity correlation
(Gonzalez 1997, Fischer & Valenti 2003)
HD 149026 planet (Saturn mass, ~70 MEarth core; Sato et al. 2005, Charbonneau et al 2006)
Marcy et al 2005
Planet-disk interactionPlanet-disk interaction Presence of substantial gas disk
means planet-disk interactions important!
Bodies in gas disk launch density waves repulsive torque between body and inner, outer disk
Jupiter-mass planets open a gap, locked into viscous evolution of disk: “Type II” inward migration
Smaller bodies: no gap, outer torques stronger: “Type I” inward migration
Presence of substantial gas disk means planet-disk interactions important!
Bodies in gas disk launch density waves repulsive torque between body and inner, outer disk
Jupiter-mass planets open a gap, locked into viscous evolution of disk: “Type II” inward migration
Smaller bodies: no gap, outer torques stronger: “Type I” inward migration
Density of planetdisk torque
Ward 1997
Geoff Bryden
Migration and accretion ratesMigration and accretion rates
Comparing the timescalesComparing the timescales
Scary result! Thus people tend to ignore/greatly reduce Type I (e.g. Thommes, Duncan & Levison 2003, Ida & Lin 2004, Alibert et al. 2005)
But is there a way to make the worst-case scenario work...?
Scary result! Thus people tend to ignore/greatly reduce Type I (e.g. Thommes, Duncan & Levison 2003, Ida & Lin 2004, Alibert et al. 2005)
But is there a way to make the worst-case scenario work...?
Accretion, no migration Accretion, no migration
Thommes & Murray 2006
Accretion + MigrationAccretion + Migration
Thommes & Murray 2006
A viscously evolving diskA viscously evolving disk
t=0
t=1 Myr
t=10 Myrs
Accretion + Migration in a viscously evolving gas diskAccretion + Migration in a viscously evolving gas disk
Thommes & Murray 2006
=10-2
Mdisk
M100 AU
M30 AU
Disk gas mass
Winners and losersWinners and losers Inner region:
growth too fast, cores lost onto star
Outer region: growth too slow relative to disk lifetime
In between: An annulus where the growth rate turns out just right
Inner region: growth too fast, cores lost onto star
Outer region: growth too slow relative to disk lifetime
In between: An annulus where the growth rate turns out just right
Thommes & Murray 2006
Method: Vary disk mass, metallicity,
For each set (MD,
,[Fe/H]), compute largest protoplanet mass when 1 MJup of gas left inside 100 AU
Results Disks with higher MD,
[Fe/H] do better There is always an
“optimal” , ~10-2-10-3; consistent with fits to T Tauri disks (Hartmann et al 1998)
Method: Vary disk mass, metallicity,
For each set (MD,
,[Fe/H]), compute largest protoplanet mass when 1 MJup of gas left inside 100 AU
Results Disks with higher MD,
[Fe/H] do better There is always an
“optimal” , ~10-2-10-3; consistent with fits to T Tauri disks (Hartmann et al 1998) Thommes & Murray 2006
Disk properties and core formationDisk properties and core formation
SummarySummary In the worst-case scenario of unmitigated Type I
migration: protoplanets in a young, massive gas disk fall onto
central star long before they can reach gas giant core size (~10 MEarth)...
...but as the gas disk dissipates, a window may open for cores to form and survive
endgame: gas envelope accretion plays large role in cleaning up rest of disk (cf. Lecar & Sasselov 2003)
Predictions Favourable disk properties: high M(0), high [Fe/H], and
~10-2 - 10-3
no giant planets (i.e. for ALMA, no gaps) in very young, massive disks
In the worst-case scenario of unmitigated Type I migration: protoplanets in a young, massive gas disk fall onto
central star long before they can reach gas giant core size (~10 MEarth)...
...but as the gas disk dissipates, a window may open for cores to form and survive
endgame: gas envelope accretion plays large role in cleaning up rest of disk (cf. Lecar & Sasselov 2003)
Predictions Favourable disk properties: high M(0), high [Fe/H], and
~10-2 - 10-3
no giant planets (i.e. for ALMA, no gaps) in very young, massive disks
“Dead zones” in disks“Dead zones” in disks Magnetorotational
instability (MRI) (Balbus & Hawley 1991) leading candidate for disk viscosity
MRI requires ionized disk, to couple it to magnetic field cosmic rays, stellar X-rays (near star)
When the full vertical column not ionized, dead zone forms (Gammie 1996, Matsumura & Pudritz 2003)
Magnetorotational instability (MRI) (Balbus & Hawley 1991) leading candidate for disk viscosity
MRI requires ionized disk, to couple it to magnetic field cosmic rays, stellar X-rays (near star)
When the full vertical column not ionized, dead zone forms (Gammie 1996, Matsumura & Pudritz 2003)
Gammie 1996
Disk evolution with a dead zoneDisk evolution with a dead zone
Dead zone: lower viscosityslower accretionpile-up of gas
Steep jumps in surface density can result
How does this affect migration...?
Dead zone: lower viscosityslower accretionpile-up of gas
Steep jumps in surface density can result
How does this affect migration...?
?
Disk torques at a surface density jump
Disk torques at a surface density jump
Type I migration: inner < outer, gas
Introducing jump in gas can reverse the torque imbalance
outer edge of a dead zone can completely stop Type I migration!
Type I migration: inner < outer, gas
Introducing jump in gas can reverse the torque imbalance
outer edge of a dead zone can completely stop Type I migration!
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Matsumura, Thommes & Pudritz, in prep.
QuickTime™ and aCinepak decompressor
are needed to see this picture.
Thommes
A “hybrid” code: N-body+gas diskA “hybrid” code: N-body+gas disk The N-body part: SyMBA (Duncan, Levison & Lee 1998)
uses Wisdom-Holman (1991) symplectic method fast for near-Keplerian systems bounded energy error
resolves close encounters The disk-evolution part: 1-D (azimuthally, vertically
averaged) Keplerian disk, Σ evolves according to
The N-body part: SyMBA (Duncan, Levison & Lee 1998) uses Wisdom-Holman (1991) symplectic method
fast for near-Keplerian systems bounded energy error
resolves close encounters The disk-evolution part: 1-D (azimuthally, vertically
averaged) Keplerian disk, Σ evolves according to
(Goldreich & Tremaine 1980, Ward 1997)
--∫(dT/dr)dr applied to planet∫(dT/dr)dr applied to planet ...Fast! Can simulate 10...Fast! Can simulate 1077 yrs in ~2 days yrs in ~2 days
-
QuickTime™ and aCinepak decompressor
are needed to see this picture.
Thommes 2005
Resonant exoplanetsResonant exoplanets
Marcy et al. 2005
The “standard model” of core accretion
The “standard model” of core accretion
Pollack et al (1996): 3 stages:1. solid core accretion
2. slow gas accretion until Mgas ~ Mcore
3. runaway gas accretion Corrections to the standard
model: Stage 1 simplified, actually
takes longer (e.g. Thommes et al. 2003)
Stage 2 HAS to be a lot shorter (can be done by lowering envelope opacity)
Pollack et al (1996): 3 stages:1. solid core accretion
2. slow gas accretion until Mgas ~ Mcore
3. runaway gas accretion Corrections to the standard
model: Stage 1 simplified, actually
takes longer (e.g. Thommes et al. 2003)
Stage 2 HAS to be a lot shorter (can be done by lowering envelope opacity)
Pollack et al. 1996
OutlineOutline Background
giant planet formation by core accretion migration by planet-disk interaction
The timescale problem Calculations of concurrent core accretion and migration in
an evolving disk A way around the timescale problem
Disk properties and the prospects for planet formation Summary
Background giant planet formation by core accretion migration by planet-disk interaction
The timescale problem Calculations of concurrent core accretion and migration in
an evolving disk A way around the timescale problem
Disk properties and the prospects for planet formation Summary