Download How do “habitable” planets form?

Making other Earths:
N-Body Simulations of the Formation of
Habitable Planets
Sean Raymond
University of Washington
Collaborators: Tom Quinn (Washington)
Jonathan Lunine (Arizona)
Habitable Zone: temperature for liquid water
Habitable Planets NEED WATER!
The Paradox
of Habitable Planet Formation
• Liquid water: T > 273 K
• To form, need icy material: T < 180 K
rocky← →icy
”snow line”
The Paradox
of Habitable Planet Formation
• Liquid water: T > 273 K
• To form, need icy material: T < 180 K
rocky← →icy
”snow line”
Local building blocks of habitable planets are dry!
So where did Earth get its water?
• Late Veneer: Earth formed dry, accreted
water from bombardment of comets, or …
Some of Earth’s “building blocks” came
from past snow line: Earth did not form
entirely from local material
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:
a) giant planet mass?
b) giant planet orbital parameters (a, e, i)?
c) surface density of solids?
Overview of Terrestrial Planet
Formation
1. Condensation of grains from Solar Nebula
2. Planetesimal Formation
3. Oligarchic Growth: Formation of
Protoplanets (aka “Planetary Embryos”)
4. Late-stage Accretion
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
Simulation Parameters
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aJUP
eJUP
MJUP
tJUP
Surface density
Position of snow line
Eccentricity
Snapshots in time from 1 simulation
Semimajor Axis
Radial Migration of Protoplanets
Simulation Results
1. Stochastic Process
2. All systems form 1-4 planets inside 2 AU,
from 0.23 to 3.85 Earth masses
3. Water content: dry to 300+ oceans
(Earth has 3-10 oceans)
Trends
1. Higher eJUP  drier terrestrial planets
2. Higher MJUP  fewer, more massive
terrestrial planets
3. Higher surface density  fewer, more
massive terrestrial planets
Effects of eJUP
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 50 times as much water as Earth
11 planets between 0.9-1.1 AU
43 planets between 0.8-1.5 AU
Conclusions
1. Most of Earth’s water was accreted during
formation from bodies past snow line
2. Terrestrial planets have a large range in
mass and water content
3. Habitable planets common in the galaxy
Conclusions
Cont’d
4. Terrestrial planets are affected by giant
planets! Can predict the nature &
habitability of extrasolar terrestrial planets
- Useful for TPF, Darwin
5. Future: develop a code to increase number
of particles by a factor of 10
Additional Information
• 2003 Paper: astro-ph/0308159
• Nature Science Updates: Aug 21, 2003
(www.nature.com)
• Email: [email protected]
• Talk to me!
Additional Slides
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!
Initial Conditions
• Assume oligarchic
growth to 3:1
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
Simulation Parameters
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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
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
Data from our Solar System
Raymond, Quinn & Lunine 2003
Distributions of Terrestrial Planets