Neal Turner Jet Propulsion Laboratory, California Institute of Technology
Protostellar Disks: Protostellar Disks: Birth, Life and DeathBirth, Life and Death
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Death of Protostellar Disks1. Origins of the gas giant planets2. Dispersal of remnant material3. Origins of the terrestrial planets4. Debris disks5. Key issues for the future
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Fischer & Valenti 2005
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Hubickyj et al. 2005
solid core
gas envelope
total
Core Accretion
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Lufkin et al. 2004
Gravitational instability with cooling time < orbital period.
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Marcy et al. 2005
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Tidal Torques in the Disk
This leads to:• Gap Formation • Orbital Migration
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From G. Bryden
Nelson et al. 2000 Type I Migration: R
ocky Cores
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Kley & Crida 2008
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Kley & Crida 2008
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Bryden & Lin 1996 Type II Migration: G
iant Planets
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Gap-Opening Criterion
Equilibrium gap width balances gap-opening tidal torques with gap-closing pressure + viscous forces.
Planetary tides overwhelm the pressure if the Hill sphere is bigger than the disk thickness:
€
a M p
3M*
⎛ ⎝ ⎜
⎞ ⎠ ⎟
1/ 3
> H
The tides overwhelm the disk viscosity if:
€
M p
M*
> 40a2Ων
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Dispersal of Remnant Disk Material
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Haisch et al. 2006
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Jayawardhana et al. 2006
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Andrews & Williams 2005
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Richling &
Yorke 2000
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Photoevaporative Clearing
Gas ionized by UV photons from the star or nearby stars heats to a temperature T ~104 K.
Outside the gravitational radius, the sound speed exceeds escape speed and the gas flows almost radially away from the star.
€
Rg =GM*μmp
kBT≈10AU
Outside a smaller critical radius, the vertical gas pressure gradient accelerates flows to escape.
€
Rc = γ −12γ
Rg ≈ 0.15 Rg
Liffman 2003National Aeronautics and Space Administration
Alexander et al. 2006
€
Rc
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Varnière et al. 2006
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Terrestrial Planet Formation
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Starting Condition is a Gas-Poor Planetesimal Disk
Sizes ~ 1km.
Weak gravitational interactions stir relative motions up to escape speed ~ 1 m/s.
Collisions and mergers produce steady growth.
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Equipartitions energy between big and small bodies
Dynamical Friction
vD
rag
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Gravitational Focusing
Cross-section for collisions is enhanced by the gravitational pull of the body.
v
b
€
bv = Rvesc
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€
σ =πR2 1+ vesc2
v 2
⎛ ⎝ ⎜
⎞ ⎠ ⎟
Gravitational Focusing
Cross-section for collisions is enhanced by the gravitational pull of the body.
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1. The protoplanets stir up the remaining planetesimals, or
1. Most of the mass is in protoplanets, so dynamical friction is ineffective.
In either case, gravitational focusing grows weak.
Runaway growth ends when…
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Nagasawa et al. 2007
Oligarchs Grow Chaos
Model Solar System
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Canup &
Asphaug 2001
Nat
iona
l Aer
onau
tics
and
Spa
ce A
dmin
istra
tion
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Debris Disks
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Dust in the Solar System
• Interplanetary dust particles are released by asteroid collisions & comet passages.
• Particle concentration in the ecliptic plane causes zodiacal light.
• Median size is 30m, but a wide range is seen.
• Even though luminosity is just 10-7 of Solar, the zodiacal light is the most luminous component of our planetary system.
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Collisional Families in the Asteroid Belt
Nesvorny et al. 2002National Aeronautics and Space Administration
The Brightest Debris Disks: Fomalhaut
Confined ring withradius 133-158 AU
Offset center –eccentric ring forcing
Dynamical modeling suggests planet;not yet confirmed
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Augereau et al. 2001
The Edge-on Warped Disk of Pictoris
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Distribution of Disk Luminosities
Based on 70 μm data, ~12% of old F5-K5 stars have disks that intercept >10-5 of the stellar flux
The grains are short-lived.
Hence disruptive collisions releasing 100x more dust than the present Solar system are common!
Trilling et al. 2008
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Brighter disks are more common for RV planet hosts
Bryden et al., submitted
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The fraction of Sun-like stars found with warm dust declines with age over ~100 Myr
Timescale for Loss of Debris
From G. BrydenNational Aeronautics and Space Administration
Debris Disks vs. Metallicity
No correlation!
(very different from strong correlation of gas giant planets with metallicity)
From G. BrydenNational Aeronautics and Space Administration
Brighter Kuiper Belts 1
From G. BrydenNational Aeronautics and Space Administration
Brighter Kuiper Belts 2
From G. BrydenNational Aeronautics and Space Administration
Key Questions for the Future
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1. What determines cloud core masses?
Alves et al. 2007
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2. How is the angular momentum removed from disks?
Mejia et al. 2005
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Asensio Ramos et al. 2007
Model H2D+ 372.4 GHz Maps
x-offset / AU
y-of
fset
/ A
U
-300 300-300
300
Intensity units 10-6 erg cm-2 s-1 sr-1
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Hot, Dense
Cold, Less Dense
Grain v=vK
3. How do planetesimals form?
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4. What remnants of planet-building remain around other stars?
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Key Questions for the Future1. What determines cloud core masses?2. How do disks lose their angular
momentum?3. How do planetesimals form?4. What remnants of planet-building
remain around other stars?
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