Exoplanets. II
What Have We Found?
1978 planets in 1488 systems as of 11/15/15
(http://exoplanet.eu/ )
1642 planets + 3787 candidates
(http://exoplanets.org)
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Detected by radial velocity/astrometry: 621
Transiting planets: 1230
Detected by microlensing: 41
Detected by imaging: 62
Detected by timing: 27
(some are duplicate entries)
Summary - Techniques
•  Direct imaging
–  Requires large planets far from star
–  Requires nearby systems
–  Best with young systems
–  Bright hot central stars help
Direct Imaging Example:
HR 8799
Why young planets are bright
Beta Pictoris
~9 AU from star
M: ~ 7 MJ
P: ~20 yrs
T: ~1600K
Summary - Techniques
•  Direct imaging
–  Young large planets far from nearby bright star
•  Astrometric Wobble
–  Requires face-on orbit; small mass ratio
–  Depends on distance: φ = a/D
Review: Velocity Wobble
Equal masses
Earth - Moon
Sun - Earth
Objects orbit their mutual center of mass
Center of the Solar System
Summary - Techniques
•  Direct imaging
–  Young large planets far from nearby bright star
•  Astrometric Wobble
–  Requires face-on orbit; small mass ratio; nearby
•  Doppler Wobble
–  Independent of distance
–  Sensitivity depends on inclination, mass ratio
First Extrasolar Planet:
51 Pegasi b
Radial velocity/ Doppler Shift
Upsilon Andromedae
Periods: 4.6, 241, 3848 days
Doppler Wobble: Gliese 876
The three planets of Gl 876:
masses = 2.5 MJ, 0.8 MJ, and 7.5
M⊕
Gliese 876
M4V star
3 planets, including the least massive known (0.75 M⊕)
Summary - Techniques
•  Direct imaging
–  Young large planets far from nearby bright star
•  Astrometric Wobble
–  Requires face-on orbit; small mass ratio; nearby
•  Doppler Wobble
–  Independent of distance
–  Sensitivity depends on inclination, mass ratio
•  Transits
–  Requires edge-on orbit
–  Short periods help
Transit Example - Ground
Transit Example - Kepler
Summary - Techniques
•  Direct imaging
–  Young large planets far from nearby bright star
•  Astrometric Wobble
–  Requires face-on orbit; small mass ratio; nearby
•  Doppler Wobble
–  Independent of distance
–  Sensitivity depends on inclination, mass ratio
•  Transits
–  Requires edge-on orbit, small separation
•  Microlensing
–  Independent of distance
Microlensing Example
OGLE 2005-BLG-390
Sensitivity to Exoplanets
Extrasolar
Planet
Detectability
Orbital Eccentricity
Planetary Densities
Densities
Extrasolar Planet Masses
Earth = 0.005
Extrasolar Planets
Planets are preferentially found around metal-rich stars
- mostly younger than the Sun.
Metallicities updated
Exoplanet Summary
•  No Solar System-like systems found
–  Many systems more compact than SS
•  Dominated by hot Jupiters
–  Densities consistent with gas giants
–  Sodium and Hydrogen have been detected
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Water Worlds
Super-Earths
Many eccentric orbits
Biases are important
Biases
•  Transits: large planets; periods < year
•  Doppler Wobble: large planets very
close to star
•  Direct imaging: large young planets far
from star
Extrasolar Planet Masses
Unbiased Masses
Tatooine
Exoplanet Comparison
How do you make a hot
Jupiter?
Existing picture of SS formation needs some changes
•  Nebular theory predictions formation of other SS
–  Suggests more planets form around metal-rich stars.
–  Jovian planets should be far from star in circular
orbits
•  Revision
–  Jovian planets formed far from star in circular orbits
–  Subsequently migrated inward
Planetary Migration
Occurs in the presence of protoplanetary disk
•  Planet moving through disk creates density waves
•  Waves exert gravitational force on planet
•  Planet loses orbital energy, moves toward star
•  Some stars show evidence of consuming planets.
•  What about Jupiter?
The Planetary Shuffle
•  Gravitational encounters → eccentric orbits
–  Two Jovian planets get close: 1 ejected,
one spirals inward, elliptical orbit
–  Small planetesimals ejected (to Oort
cloud), Jovian planet loses orbital energy
•  Happened in our SS
•  Resonances
–  Lead to eccentric orbits
–  Can yield migration or ejection
A Model for Our Solar System
Series of papers in Nature in 2005
•  Solar System: Sun, planets, debris disk of planetesimals
–  Planets accrete or scatter planetesimals
–  Angular momentum exchange causes planetary migration
•  Jupiter moves in, Saturn, Uranus, and Neptune move out
•  1:2 orbital resonance between Jupiter and Saturn reached
–  Kick in eccentricities, destabilitization of orbits
–  Uranus and Neptune scattered outward, switch positions
–  Small bodies move inward
•  Interactions explain current orbital radii and eccentricities
•  1:2 resonance explains late heavy bombardment period
•  Initial geometry can give resonance (and hence scattering) at
right time.
•  Asteroids will also be perturbed at this time.
Extreme Planets
•  Rare, hence need large numbers to find
•  Opportunity to study the limits of planet
formation and survival
•  One “pathological” case may provide
more information than many “normal”
cases
KIC 8462852
•  F star.
•  Deep aperiodic dips, up to 20% blockage
HD189733b
(a hot Jupiter)
•  T ~ 3000K
•  Winds to 5400
mph
55 Cnc e
Brightness varied factor of 3 in 2 days
Other oddities
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Salt clouds
Iron hydride precipitation
Hot Jupiters
Close-in multiple systems
Extrasolar Planetary Systems
55 Cancri (G5V): 5 planets
• 1 MU 0.4 AU
• 1 MJ 0.15 AU
• 1 Ms 0.25 AU
• 0.5 MJ 0.8 AU
• 4 MJ 5 AU