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)

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: giant planet mass? giant planet orbital parameters (a, e, i)? c) surface density of solids?

Overview of Terrestrial Planet Formation Condensation of grains from Solar Nebula Planetesimal Formation Oligarchic Growth: Formation of Protoplanets (aka “Planetary Embryos”) 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 aJUP eJUP MJUP tJUP Surface density Position of snow line

Snapshots in time from 1 simulation Eccentricity Semimajor Axis

Radial Migration of Protoplanets

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)

Trends Higher eJUP  drier terrestrial planets Higher MJUP  fewer, more massive terrestrial planets 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 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

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

Additional Information 2003 Paper: astro-ph/0308159 Nature Science Updates: Aug 21, 2003 (www.nature.com) Email: raymond@astro.washington.edu 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 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