1. (Institute for Advanced Study)
Properties of Extrasolar Planets
Roman Rafikov
(Institute for Advanced Study)
Methods of detection
Characterization
Theoretical ideas
Future prospects

2. Methods of detection
Methods of detection

3. Methods of detection
Pulsar timing
Planetary motion around pulsar causes periodic pulsar displacement around the center of mass by light-seconds for Earth-like planet ( g ) at AU from the neutron star ( ) – well within current detection capabilities.
m sin i degeneracy (broken in PSR by planetary interaction)
First discovered extrasolar system: PSR (Wolszczan and Frail 1992) A B C
Mass, M_Earth
0.015
3.4
2.8
Eccentricity
0.0
0.018
0.026
Period, days
25.3
66.5
98.2
Sem. axis, AU
0.19
0.36
0.47
Second suggested system: PSR (Backer et al. 1993)
Planet NS WD
Similar to Solar System
Recently confirmed (Sigurdsson et al 2003) to have a giant planet in a wide eccentric orbit.
Similar to nearby EGP systems.

4. Radial Velocity Variations
Methods of detection
Radial Velocity Variations
Planetary motion moves star around with velocity Jupiter-mass planet at 1 AU causes stellar motion with velocity 30 m/s.
Searching for periodic Doppler shifts can detect planet (like companion in spectroscopic binary).
Method suffers from m sin i degeneracy
Velocity noise can be pushed down to 1-2 m/s
Up to now the most successful technique – more than 100 planets detected
First detection Peg (Mayor & Queloz 1995)
Butler et al 2004
GL 436
Keck

5. Methods of detection
Planetary Transits
Jupiter-size planet passing in front of the star causes stellar flux drop (eclipse) by for ~ hours.
Transit probability for AU
Combined with RV data gives mass (sin i =1)
The only method which gives planetary size
Expect signal also in reflected light
Systematic effects (blends, etc.)
First transit detection in previously known planetary system HD (Charbonneau et al 2000)
More than 20 transit searches are underway
1 planet detected (4 more – OGLE transits )
Great ancillary science for time-variable phenomena searches (GRB monitoring campaigns, microlensing searches)
TrES-1 (Alonso et al 2004)

6. Methods of detection
Microlensing
Bond et al 2004
Gravitational lensing by binary systems leads to easily recognizable pattern of magnification.
Light curve fitting yields system parameters and may be used for planet searches.
Cannot repeat observation
Usually distance is unknown
Stellar brightness unimportant
Bond et al 2004
OGLE 2003-BLG-235/MOA 2003-BLG-53 (first planet detection by microlensing)
Planetary mass
Stellar mass
Semimajor axis
Distance to the system

7. Methods of detection
Astrometry
Jupiter-mass planet at 1 AU moves its star around by which for AU at 10 pc results in 100 µas displacement on the sky.
Benedict et al (2002) may have detected astrometric signal from previously known planet Gliese 876b (~ 2 M_J, 0.3 AU) using fine guidance sensors on HST.
Sensitive to massive and distant planets – requires long time baseline
In combination with RV data breaks m sin i degeneracy and determines mass and orbit orientation (similar to observations of stars near the Sgr A*)
Requires exquisite astrometric accuracy.
Future missions should revolutionize this field (Keck Interferometer, SIM).

8. Methods of detection

9. Results: characteristics of extrasolar planets
Characterization
Results: characteristics of extrasolar planets

10. Dynamical Characteristics
Characterization
General Statistics
120 planetary systems, 138 planets, 15 multiple systems
5 by transits
4 by pulsar timing
1 by microlensing
110 by radial velocity searches
Dynamical Characteristics
Unusual distribution of semimajor axes – many planets very close to the star
- Incomplete beyond several AU
- Very significant within 1 AU (“Hot Jupiters”)
Predominance of planets with large eccentricities for periods longer than several days
- closest ones are circularized by stellar tides
- e-distribution is close to that of binary stars
Very different from Solar System planets!

11. Characterization
Physical Properties
Planetary sizes consistent with expectations except that
Radius of HD is too large to be accomodated by simple models.
High masses (only recently RV started probing Neptune mass range).
Larger number of lower mass planets.
“Brown dwarf desert” – relative lack of planets heavier than
Clear correlation between the metallicity of the parent main-sequence star and the probability of hosting planet.
Pulsar planet in M4 may have formed in very low-Z environment; planets around PSR may have formed from very high-Z material.

12. Simulation from (Vidal-Madjar et al 2003)
Characterization
HD (a.k.a. “Osiris”)
HST transit curve (Brown et al 2001)
Mass , period 3.5 d, AU
Parent star (G0 V) at a distance of 47 pc
Radius of is a challenge for theory
Direct probe of planetary atmosphere
Na absorption detected in transit – atmospheric signature (Charbonneau et al 2002)
Extended absorbing region in H-alpha – envelope of escaping hydrogen (Vidal-Madjar et al 2003)
Evidence for oxygen and carbon in this escaping envelope
Gas loss rate g/s
Evaporation time is more than a Hubble time
Simulation from (Vidal-Madjar et al 2003)
(Vidal-Madjar et al 2004)
Planet is safe from evaporation!

13. Theoretical ideas
Theoretical Ideas

14. Dynamical peculiarities
Theoretical ideas
Dynamical peculiarities
Tight planetary orbits
Evidence for planet migration – planets did not form where we observe them
They moved there as a result of the tidal interaction with the gaseous disk
Why did they stop? What is the parking mechanism?
Bryden
Large orbital eccentricities
Possible signature of planet-planet gravitational scattering
Could have also been caused by the tidal planet-disk interaction
Resonant interaction of migrating planets
Rasio & Ford 1996
We don’t really know these things very well

15. 1 M_J planet (Lubow et a al 2003)
Theoretical ideas
Peculiarities of physical structure
Mass distribution
Mass distribution arises from interplay of gas accretion and gravitational interaction of growing planet with surrounding gas disk
Formation of “gap” can probably explain the “brown dwarf desert”
Current observed overabundance of high mass planets can be purely a selection effect
Metallicity dependence
Can be accounted for assuming that giant planets form via the gas accretion onto the rocky cores
Could be a signature of stellar pollution by accreting planetary material (e.g. migrating planets which failed to hit the brake)
1 M_J planet (Lubow et a al 2003)

16. Future prospects
Future Prospects

17. Kepler Space-based Photometer ( 0.95-m aperture )
Future prospects
Kepler
Space-based Photometer ( 0.95-m aperture )
Photometric One-Sigma Noise <2x10-5
Monitor 100,000 main-sequence stars for planets.
Mission lifetime of 4 years.
Launch date – October 2007
Transits of terrestrial planets:
- About 50 planets if most have R ~ R_Earth,
Modulation of the reflected light from giant inner planets:
- About 870 planets with periods less than one week.
Transits of giant planets:
- About 135 inner-orbit planet detections along with albedos for about 100 of them.

18. SIM (Space Interferometry Mission)
Future prospects
SIM
(Space Interferometry Mission)
Precision astrometry on stars to V=20
Optical interferometer on a 10-m structure
Global astrometric accuracy: 4 microarcseconds (µas)
Typical observations take ~1 minute; ~ 5 million observations in 5 years
Launch date - February 2010
Search for terrestrial planets around the nearest stars
(1 µas)
“Broad survey" for Neptune-size planets around stars (3 µas)
Giant planets around young stars

19. Future prospects
TPF
(Terrestrial Planet Finder)
Two complementary space observatories: a visible-light coronagraph and a mid-infrared formation-flying interferometer.
TPF coronagraph launch is anticipated around 2014.
TPF interferometer launch is anticipated before 2020.
- Survey nearby stars looking for terrestrial-size planets in the "habitable zone“.
- Follow up brightest candidates with spectroscopy, looking for atmospheric signatures, habitability or life itself.
- Will detect and characterize Earth-like planets around as many as 150 stars up to 15 pc away.
Goals:

20. Conclusions
More than 100 planets are now known around main sequence stars and neutron stars, among them 15 multiple systems.
They are detected by 4 different methods:
- Radial velocity searches
- Pulsar timing
- Transits
- Microlensing
Most extrasolar planets exhibit unusual dynamical characteristic: small orbits and high eccentricities.
Their physical properties are similar to those of giant planets in the Solar System (Jupiter and Saturn).
In the next 10 years at least 3 space borne missions will open up new horizons in this field. More than 30 are currently underway.