The search for habitable planets and the quest to understand their origins D.N.C. Lin KIAA, Peking University, University of California, Santa Cruz, Kavli Institute for Theoretical Physics China Beijing, China May 26th, 2007 30 slides

High-precision spectroscopy 2/30

Mass-period distribution A continuous logarithmic period distribution A pile-up near 3 days and another pile up near 2-3 years Does the mass function depend on the period? Is there an edge to the planetary systems? Does the mass function depend on the stellar mass or [Fe/H]? 3/30

Avenues of planet formation 4/30

Inner disks disappear ~ 10 Myr Hillenbrand & Meyer 2000 1.0 r Oph CrA N2024 0.8 N1333 Trap Mon R2 Taurus 0.6 LHa101 L1641y N7128 Fraction of disks 0.4 ONC L1641b Lupus IC 348 Cha N2264 The fraction of stars with inner disks (r < 1 AU), as measured by near infrared excesses, decreases in young clusters on a time scale of order 10 Myr. The typical lifetime is entirely adequate to build up planetesimals and even some giant planets. 0.2 TW Hyd Pleiades Hyades 0.0 a Per Ursa Major 0.1 1 10 100 1 Gyr Age (Myr) 5/30 Gas accretion rate

Chondritic meteorites Limited size range, sm-cm, Glass texture, flash heating, Age difference with CAI’s, Matrix glue & abundance, Weak tensile strength. Formation timescale 2-3 Myr 6/30

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From planetesimals to embryos Feeding zones: D ~ 10 rHill Isolation mass: Misolation ~ S1.5 a3 Initial growth: (runaway) 8/30

Disk-planet tidal interactions type-I migration type-II migration Lin & Papaloizou (1985),.... Goldreich & Tremaine (1979), Ward (1986, 1997), Tanaka et al. (2002) planet’s perturbation viscous diffusion disk torque imbalance viscous disk accretion 9/30

(Mass) growth vs (orbital) decay Embryos’ migration time scale Outer embryos are better preserved only after significant gas depletion Critical-mass core:Mp=5Mearth Loss due to Type I migration Jovian-mass ESP’s are rare around late-type stars 10/30

Dependence on M* 1) hJ increases with M* 2) Mp and ap increase with M* Do eccentricity and multiplicity depend on M*? 11/30

Planetary interior: diverse structure & Fe/H HD149026b: 67 earth-mass core 12/30

Giant impacts Diversity in core mass Spin orientation Survival of satellites Retention of atmosphere Late bombardment of planetesimals 13/30

The period distribution: Type II migration 14/30 Disk depletion versus migration

Stellar metallicity, mass loss, & circularization of hot Jupiters Early formation Extensive migration High mortality rate Planetary mass loss Tidal circularization Signs of evolution? 15/30

short-period cutoff Prediction: 90% disruption of hot Jupiters Stopping mechanisms: 1) magnetospheric cavity 2) stellar tidal barrier 3) protoplanetary consumption 4) planetary tidal disruption Ogilvie Prediction: 90% disruption of hot Jupiters Bimodal Q*: prevalence of 1-day planets Tidal inflation Bodenheimer 16/30

Transits: atmosphere & structure 17/30 29/48

period cutoffs depletion vs growth time Prediction: period fall-off 18/30 Prediction: period fall-off Test: gravitational lense Ice giants: Collisions vs ejections

Multiple systems Diversity in mass distribution Resonant system with limited mass What fraction of Jovian mass planets reside in multiple systems? Is multiplicity more correlated with [Fe/H] or M* than single planets? 19/30

Multiple planets a) Induced formation of multiple giants b) Resonant planets c) Formation time scale comparable to migration Bryden 20/30

Post Depletion Dynamical Stability Dynamical filling factor: e excitation & chaos Rayleigh distribution 21/30

Migration-free sweeping secular resonances Resonant secular perturbation Mdisk ~Mp (Ward, Ida, Nagasawa) Ups And Transitional disks 22/30

Sweeping secular resonance in ESP’s Triple system around Ups And Rotational flattening & precession Nagasawa, Mardling Excitation of e & tidal inflation in HD209458 & disruption in 55 Can Gu, Ogilvie, Bodenheimer, Laughlin 23/30

Mean motion resonance capture Migration of gas giants can lead To the formation of hot earth Implication for COROT Zhou Tidal decay out of mean motion resonance (Novak & Lai) Impact enlargement Rejuvenation of gas Giant. HD 209458b (Guillot) 24/30 Detection probability of hot Earth Narayan, Cumming

Dynamical shake up (Nagasawa, Thommes) Bode’s law: dynamically porous terrestrial planets orbits with low eccentricities with wide separation 25/30

Migration, Collisions, & damping Clearing of the asteroid belt Earlier formation of Mars Sun ward planetesimals Late formation (10-50 Myr) Giant-embryo impacts Low eccentricities, stable orbits 26/30

Giant impact & lunar formation Lunar material similar to the Earth’s crust. Formation after the differentiation (30 Myr) Mars-size impactor Post impact circular orbit Formation after 60 Myr Formation on 30-60 Myr 27/30

Last melting events of chondrules Flash heating: Large S : evaporation Medium S : melting Small S : preservation 28/30

Frequency of Earth 29/30

Sequential accretion scenario summary Damping & high S leads to rapid growth & large isolation masses. Jupiter formed prior to the final assemblage of terrestrial planets within a few Myrs. 2) Emergence of the first gas giants after the disk mass was reduced to that of the minimum nebula model. 3) Planetary mobility promotes formation & destruction. 4) The first gas giants induce formation of other siblings. 5) Shakeup led to the dynamically porous configuration of the inner solar system & the formation of the Moon. 6) Earths are common and detectable within a few yrs! 30/30

Dependence on the stellar [Fe/H] Santos, Fischer & Valenti Frequency of Jovian-mass planets increases rapidly with [Fe/H]. But, the ESP’s mass and period distribution are insensitive to [Fe/H]! Is there a correlation between [Fe/H] & hot Jupiters ? Do multiple systems tend to associated with stars with high [Fe/H]? 4/43

Disk evolution only external disk but accreting star Protostellar disks: Gas/dust = 100 Dabris disks: Gas/dust = 0.01 Transitional disks only external disk but accreting star 6/43

From dust to planetesimals Retention of heavy elements: tgrowth~Sdust but tdecay ~ Sgas 6a/43

Potential observational signatures Coexistence of gas and solid phase volatile ices Evolution of snow line 8/43

Condensation sequence Meteorites: Dry, chondrules & CAI’s Icy moons 9/43

Signs of Crystalline grains Bouwman Apai 8a/43

Growth during gas depletion Rapid damping: many small residual embryos. Slow damping: large eccentricity Delicate balance: Kominami & Ida Separation of eccentricity Excitation and damping is Needed! 12/43

Competition: M growth & a decay 10 Myr 1 Myr 0.1 Myr Limiting isolation mass Hyper-solar nebula x30 Metal enhancement does not always help! need to slow down migration 13a/43

Embryos’ type I migration (10 Mearth) Cooler and invisic disks Warmer disks 14/43

Accretion onto cores Pollack et al Challenges: Core growth: perturbation slow down & planetesimal gaps (Ida) Radiation transfer efficiency grain survival & opacity (Podolak) 3) Low global Sdust (Bryden) Korycansky Bodenheimer 18/43

Flow into the Roche lobe H/a=0.07 Bondi radius (Rb=GMp /cs2) Hill’s radius (Rh=(Mp/3M* )1/3 a) Disk thickness (H=csa/Vk) Rb/ Rh =31/3(Mp /M*)2/3(a/H)2 decreases with M* H/a=0.04 21/43

Preferred cradles of gas giants: snow line Limited by: Isolation slow growth 17/43

Effect of type I & II migration Habitable planets M/s accuracy 22/43

The mass distribution Origin of desert: Runaway gas accretion Bryden 28/43

Metallicity dependence [Fe/H] Two determining factors for the slope: Heavy element retention efficiency, growth vs accretion Growth rate and isolation mass of embryos 29/43

Stellar mass-metallicity More data needed for high and low-mass stars 30/43

Sweeping clear of planetesimals Sweeping secular resonance & gas drag b Pic:Duncan, Nagasawa 37a/43

Formation of warm Neptunes Jupiter-Saturn secular interaction & multiple extrasolar systems Relativistic detuning in m Arae 39/43

A 2 Mearth “hot rock” planet in a 7-d orbit observed for 6 months with APF @ 1.3 m/s precision Easily detected! But this short-period planet is much too hot for habitability 40a/43

1 Mearth planet in a 35-d habitable-zone orbit around a nearby M dwarf – observed for 6 months with a 9-telescope global array @ 2.0 m/s precision Easy detection! 42/43

Outstanding issues: Frequency of planets for different stellar masses Completeness of the mass-period distribution Signs of dynamical evolution Mass distribution of close-in planets: efficiency of migration Halting mechanisms for close-in planets Origin of planetary eccentricity Formation and dynamical interaction of multiple planetary systems Internal and atmospheric structure and dynamics of gas giants Satellite formation Low-mass terrestrial planets