How do Habitable Planets Form

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How do Habitable Planets Form?

• Sean Raymond
• University of Washington

Collaborators Tom Quinn (Washington) Jonathan
Lunine (Arizona)
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Habitable Zone temperature for liquid water
HZ is function of planets atmosphere, type
age of star
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Habitable Planets NEED WATER!
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The Paradox of Habitable Planet Formation

• Liquid water T gt 273 K
• To form, need icy material T lt 170 K

?icy
rocky?
snow line
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The Paradox of Habitable Planet Formation

• Liquid water T gt 273 K
• To form, need icy material T lt 170 K

?icy
rocky?
snow line
Local building blocks of habitable planets are
dry!
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So where did Earth get its water?

• Late Veneer Earth formed dry, accreted water
  from bombardment of comets, or

? ? ? Comets ? ? ?
Asteroid Belt
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So where did Earth get its water?

• Late Veneer Earth formed dry, accreted water
  from bombardment of comets, or
• ?Some of Earths building blocks came from past
  snow line, in outer Asteroid Belt Earth did not
  form entirely from local material

? ? ? Comets ? ? ?
Asteroid Belt
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To guide the Habitable Planet Search (TPF,
Darwin), we need to know

• 1. Are habitable planets common?
• 2. Can we predict the nature of extrasolar
  terrestrial planets from knowledge of
• Giant planet mass?
• Giant planet orbital parameters (a, e, i)?
• c) Metallicity of host star?

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Overview of Terrestrial Planet Formation

• Condensation of grains from Solar Nebula
• Planetesimal Formation
• Oligarchic Growth Formation of Protoplanets (aka
  Planetary Embryos)
• Late-stage Accretion

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Simulation Parameters

• aJUP Giant planets orbital radius
• eJUP Giant planets orbital eccentricity
• MJUP Giant planets mass
• tJUP Giant planets time of formation
• Surface density ? stellar metallicity
• Position of snow line

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Snapshots in time from 1 simulation
Eccentricity
Semimajor Axis
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Radial Migration of Protoplanets
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Simulation Results

• Stochastic Process
• All systems form 1-4 planets inside 2 AU, from
  0.23 to 3.85 Earth masses
• Water content dry to 300 oceans (Earth has
  1-10 oceans)

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Trends

• Higher eJUP ? drier terrestrial planets
• Higher MJUP ? fewer, more massive terrestrial
  planets
• Higher surface density ? fewer, more massive
  terrestrial planets

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Effects of eJUP
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Habitability

• In most cases, planet forms in 0.8-1.5 AU
• In 1/4 of cases, between 0.9-1.1 AU
• Range from dry planets to water worlds with 30
  times as much water as Earth

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43 planets between 0.8-1.5 AU
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11 planets between 0.9-1.1 AU
(1)
(2)
(3)
(4)
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What might planets around other stars look like?
(1) aJUP 4 AU
(2) MJUP 10 MEARTH
(3) MJUP 1/3
(4) Solar System
Images from NASA
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Conclusions

• Most of Earths water was accreted during
  formation from bodies past snow line
• Terrestrial planets have a large range in mass
  and water content
• Habitable planets common in the galaxy

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Conclusions Contd

• Terrestrial planets are affected by giant
  planets! Can predict the nature habitability
  of extrasolar terrestrial planets
• - Useful for TPF, Darwin
• Future develop a code to increase number of
  particles by a factor of 10

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Additional Information

• 2004 Icarus paper, Making other Earths...
• http//www.astro.washington.edu/raymond
• Papers by John Chambers
• Talk to me!

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Additional Slides
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What is a habitable planet?

• Habitable Zone Temperature for liquid water on
  surface
• 0.8 to 1.5 AU for Sun, Earth-like atmosphere
• varies with type of star, atmosphere of planet
• Habitable Planet Need water!

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Initial Conditions

• Assume oligarchic growth to 31 resonance with
  Jupiter
• Surface density jumps at snow line
• Dry inside 2 AU, 5 water past 2.5 AU, 0.1 water
  in between
• Form super embryos if Jupiter is at 7 AU

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Simulation Parameters

• aJUP 4, 5.2, 7 AU
• eJUP 0, 0.1, 0.2
• MJUP 10 MEARTH, 1/3, 1, 3 x real value
• tJUP 0 or 10 Myr
• Surface density at 1 AU 8-10 g/cm2
• Surface density past the snow line

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Simulations

• Collisions preserve mass
• Integrate for 200 Myr with serial code called
  Mercury (Chambers)
• 6 day timestep
• currently limited to 200 bodies
• 1 simulation takes 2-6 weeks on a PC

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Data from our Solar System
Raymond, Quinn Lunine 2003
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Oligarchic Growth growth by the few

• Protoplanets grow faster closer to the Sun!
• Take approx. 10 Myr to form at 2.5 AU
• Mass, distribution depend on surface density

Kokubo Ida 2002
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Distributions of Terrestrial Planets