The search for habitable planets andthe 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 distributionA pile-up near 3 days and another pile up near 2-3 yearsDoes 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]?

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Avenues of planet formation

4/30

Hillenbrand & Meyer 2000

Inner disks disappear ~ 10 Myr

Per

Pleiades Hyades

Ursa Major

TW Hyd

N2264

IC 348

L1641bLupus

Cha

ONC

N7128

LH101

Taurus

L1641y

Mon R2

N1333

CrA

Trap

N2024

Oph

0.1 1 10 100 1 Gyr

Age (Myr)

0.0

0.2

0.4

0.6

0.8

1.0Fr

act

ion

of

dis

ks

5/30 Gas accretion rate

Chondritic meteorites

1) Limited size range, sm-cm,2) Glass texture, flash heating, 3) Age difference with CAI’s,4) Matrix glue & abundance,5) Weak tensile strength.6) Formation timescale 2-3 Myr 6/30

7/30

Feeding zones: 10 rHill

Isolation mass:Misolation ~ a3

From planetesimals to embryos

Initial growth: (runaway)

8/30

type-II migration

planet’s perturbation

viscous diffusion

type-I migration

disk torque imbalance

MyrAU1

05.023

23

*

g

SNg,Imig,

a

M

M

M

M

op

MM )10010( MM )11.0(

MyrAU1

10

2

12

1

*

o3

J

p

g

SNg,IImig,

a

M

M

M

M

Disk-planet tidal interactions

viscous disk accretion

Goldreich & Tremaine (1979), Ward (1986, 1997), Tanaka et al. (2002)

Lin & Papaloizou (1985),....

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(Mass) growth vs (orbital) decay

Loss due to Type I migrationJovian-mass ESP’s are rare aroundlate-type stars

MyrAU1)(

)0(04.0

*

o

g

gImig,

43

a

M

M

t

Embryos’ migration time scale

511

AU1)0(

)(

g

g

Imig,

embryo

at

Outer embryos are better preserved only after significant gas depletion

Critical-mass core:Mp=5Mearth

MyrAU1)(

)0(01.0

23

21

*

g

gImig,

a

M

M

t o

10/30

Dependence on M*

1) J 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 impacts1) Diversity in core mass2) Spin orientation3) Survival of satellites4) Retention of atmosphere

13/30Late bombardment of planetesimals

The period distribution:Type II migration

Disk depletion versus migration14/30

Stellar metallicity, mass loss, & circularization of hot Jupiters

1) Early formation2) Extensive migration3) High mortality rate4) Planetary mass loss5) Tidal circularization

6) Signs of evolution?

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short-period cutoffStopping mechanisms: 1) magnetospheric cavity 2) stellar tidal barrier 3) protoplanetary consumption4) planetary tidal disruption

Prediction: 90% disruption of hot JupitersBimodal Q*: prevalence of 1-day planets

Ogilvie

Tidal inflationBodenheimer

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Transits: atmosphere & structure

29/48

17/30

period cutoffs

depletion vs growth time

Ice giants:Collisions vs ejections

Prediction: period fall-offTest: gravitational lense

18/30

Multiple systems

Diversity in mass distributionResonant system with limited massWhat fraction of Jovian mass planets reside in multiple systems?Is multiplicity more correlated with [Fe/H] or M* than single planets?

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Multiple planets

a) Induced formation of multiple giantsb) Resonant planetsc) Formation time scalecomparable to migration

Bryden

20/30

Post Depletion Dynamical Stability Dynamical filling factor: e excitation & chaos

21/30 Rayleigh distribution

Migration-free sweeping secular resonances

Resonant secularperturbationMdisk ~Mp

(Ward, Ida, Nagasawa)Ups And

Transitional disks

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Sweeping secular resonance in ESP’s

Excitation of e & tidal inflation in HD209458 &disruption in 55 Can Gu, Ogilvie, Bodenheimer, Laughlin

Rotational flattening & precession Nagasawa, Mardling

Triple system around Ups And

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Mean motion resonance capture

Tidal decay out of mean motion resonance(Novak & Lai)

Impact enlargementRejuvenation of gas Giant. HD 209458b(Guillot)

Detection probability of hot Earth Narayan, Cumming

Migration of gas giants can lead To the formation of hot earthImplication for COROT

Zhou

24/30

Dynamical shake up (Nagasawa, Thommes)Bode’s law: dynamically porous terrestrial planetsorbits with low eccentricities with wide separation

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Migration, Collisions, & damping

1. Clearing of the asteroid belt2. Earlier formation of Mars3. Sun ward planetesimals

A. Late formation (10-50 Myr)B. Giant-embryo impacts C. Low eccentricities, stable orbits

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Giant impact & lunar formation1) Lunar material similar to the Earth’s crust.2) Formation after the differentiation (30 Myr)3) Mars-size impactor4) Post impact circular orbit

Formation after 60 Myr

Formation on 30-60 Myr27/30

Last melting events of chondrules

Flash heating:Large : evaporationMedium : meltingSmall : preservation

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Frequency of Earth

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Sequential accretion scenario summary1) Damping & high 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!

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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]?

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Disk evolution

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Protostellar disks:Gas/dust = 100

Dabris disks:Gas/dust = 0.01

only external disk but accreting star

Transitionaldisks

From dust to planetesimals

Retention of heavy elements:growth~dust but decay ~ gas 6a/43

Potential observational signatures

Coexistence of gas and solid phase volatile icesEvolution 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 eccentricityExcitation and damping is Needed!

12/43

Competition: M growth & a decay

Hyper-solar nebulax30

Metal enhancement does not always help! need to slow down migration

10 Myr 1 Myr0.1 Myr

Limiting isolationmass

13a/43

Embryos’ type I migration (10 Mearth)

Cooler and invisic disks

Warmer disks14/43

Accretion onto cores

Challenges:1) Core growth: perturbation slowdown & planetesimal gaps (Ida)2) Radiation transfer efficiencygrain survival & opacity (Podolak)3) Low global dust (Bryden)

Pollack et al

Bodenheimer

Korycansky

18/43

Flow into the Roche lobe

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*

21/43

H/a=0.07

H/a=0.04

Preferred cradles of gas giants: snow line

Limited by:Isolation slow growth

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Effect of type I & II migration

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Habitable planets

M/s accuracy

The mass distribution

Origin of desert:Runaway gas accretion

Bryden

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Metallicity dependence

[Fe/H]

Two determining factors for the slope:1) Heavy element retention efficiency, growth vs accretion2) Growth rate and isolation mass of embryos

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Stellar mass-metallicity

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More data needed for highand low-mass stars

Sweeping clear of planetesimals

Sweeping secularresonance & gas drag Pic:Duncan, Nagasawa

37a/43

Formation of warm Neptunes

Jupiter-Saturn secular interaction& multiple extrasolar systems

Relativistic detuning in Arae39/43

A 2 Mearth “hot rock” planet in a 7-d orbit observed for 6 months with APF @ 1.3 m/s

precision

Easily detected!Easily detected!

But this short-period planet But this short-period planet is is muchmuch too hot for habitability 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!Easy detection!

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Outstanding issues:

1) Frequency of planets for different stellar masses2) Completeness of the mass-period distribution3) Signs of dynamical evolution4) Mass distribution of close-in planets: efficiency of migration5) Halting mechanisms for close-in planets6) Origin of planetary eccentricity7) Formation and dynamical interaction of multiple planetary systems8) Internal and atmospheric structure and dynamics of gas giants9) Satellite formation10) Low-mass terrestrial planets