1. Sean Raymond University of Washington
Making other Earths: N-Body Simulations of the Formation of Habitable Planets
Sean Raymond
University of Washington
Collaborators: Tom Quinn (Washington)
Jonathan Lunine (Arizona)

2. Habitable Zone: temperature for liquid water

3. Habitable Planets NEED WATER!

4. The Paradox of Habitable Planet Formation
Liquid water: T > 273 K
To form, need icy material: T < 180 K
rocky←
→icy
”snow line”

5. 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!

6. 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

7. 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) surface density of solids?

8. Overview of Terrestrial Planet Formation
Condensation of grains from Solar Nebula
Planetesimal Formation
Oligarchic Growth: Formation of Protoplanets (aka “Planetary Embryos”)
Late-stage Accretion

9. 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

10. Simulation Parameters
aJUP
eJUP
MJUP
tJUP
Surface density
Position of snow line

11. Snapshots in time from 1 simulation
Eccentricity
Semimajor Axis

12. Radial Migration of Protoplanets

13. 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 3-10 oceans)

14. Trends Higher eJUP  drier terrestrial planets
Higher MJUP  fewer, more massive terrestrial planets
Higher surface density  fewer, more massive terrestrial planets

15. Effects of eJUP

16. Habitability In most cases, planet forms in 0.8-1.5 AU
In ~1/4 of cases, between AU
Range from dry planets to “water worlds” with 50 times as much water as Earth

17. 11 planets between AU

18. 43 planets between AU

19. Conclusions
Most of Earth’s 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

20. Conclusions Cont’d
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

21. Additional Information
2003 Paper: astro-ph/
Nature Science Updates: Aug 21, 2003 (
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22. Additional Slides

23. 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!

24. 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

25. 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

26. 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

27. Data from our Solar System
Raymond, Quinn & Lunine 2003

29. Distributions of Terrestrial Planets