1. 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

2. High-precision spectroscopy
2/30

3. 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

4. Avenues of planet formation
4/30

5. 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

6. 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

7. 7/30

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

9. 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

10. (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

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

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

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

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

15. 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

16. 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

17. Transits: atmosphere & structure
17/30
29/48

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

19. 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

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

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

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

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

24. 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 b
(Guillot)
24/30
Detection probability of hot Earth Narayan, Cumming

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

26. 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

27. 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 Myr
27/30

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

29. Frequency of Earth
29/30

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

33. 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

34. 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

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

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

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

38. Signs of Crystalline grains
Bouwman
Apai
8a/43

39. 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

40. 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

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

42. 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

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

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

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

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

47. 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

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

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

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

51. 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

52. 1 Mearth planet in a 35-d habitable-zone orbit around a nearby M dwarf – observed for 6 months with a 9-telescope global 2.0 m/s precision
Easy detection!
42/43

53. 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