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Transcript 
Extra-solar planets
(Exoplanets)
Ian Short
Department of Astronomy and Physics
Institute for Computational Astrophysics
Saint Mary’s University
Another star system??
• Nearest star 40 trillion km
away
• Neptune is 4.5 billion km from
Sun
• Planet brightness
< 1/1,000,000 Star brightness
• Glare of host star
Host star “wobble”
Planet and star both orbit centre of mass
Planet and star both orbit centre of
mass
Doppler effect to see “wobble”
Radial velocity (RV) variation
Doppler effect
• Orientation at least somewhat
edge-on
• Radial velocity (RV) change <
1 part in 1/10,000,000
• About 350 planets
• Can get orbital size, shape,
velocity
• Lower limit to planet mass
Transiting exoplanet
Exoplanet transit
• Edge-on orientation
• Brightness change
< 1 in 100
• Measure light curve
• About 50 systems
• Get planet radius and
mass
Exoplanet properties
The known population (so far…)
• 358 found
• Almost all found since
1995
• 10% solar-type stars
have planets
• Most are gas giants
(Jovian) (bias?)
• Most have orbits smaller
than Earth’s (bias?)
Most are Jovian planets
Gas-giants - Jupiter like
May be a bias effect
http://exoplanets.org
Extra slides:
(Not shown during presenatation)
Multi-planet systems
20 known
55 Cancri: 5 planets!
Multi-planet systems
Future: More detections with spacebased instruments
• COROT: launched
Dec 2006
• MOST: launched
2003 (Canada!)
Stellar spectroscopy
Doppler effect to measure motion
of remote object
Doppler shift technique to detect
stellar “wobble”
Orbital plane orientation
• Face-on
• Edge-on
Orbital plane orientation
Intermediate (oblique) orientation
Various types of data from extrasolar planetary
system:
Spectrum, light curve if transiting
Adaptive optics
Laser guide star and Deformable mirror
Direct imaging
Eg. Fomalhaut (α Piscis Austrinis)
Fomalhaut’s planet
(Distance = 25 Light Years)
• Adaptive optics
• Coronograph
• Infrared (IR) band
• “Roll subtraction”
Fomalhaut’s planet
Artist’s conception
Direct imaging of extrasolar planets
Habitable planets?
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