AS101 Lesson 9
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29 Terms
Direct detection
Actual imaging of exoplanet light; very difficult because star is much brighter
Indirect detection
Infer planet from effects on parent star/light
Two main star-motion techniques
Astrometry and Doppler (radial velocity)
Astrometry
Measure tiny side-to-side wobble of star caused by orbiting planet
What astrometry reveals
Planet presence, orbit size, mass estimate (with enough data)
Doppler technique
Measure star moving toward/away from us using spectral shifts
Blueshift in Doppler method
Star moving toward Earth
Redshift in Doppler method
Star moving away from Earth
What Doppler method reveals
Planet presence, orbital period, orbit shape, minimum mass
Why star moves with planet
Star and planet orbit common center of mass (barycenter)
Transit method
Planet passes in front of star causing slight brightness dip
What transit method reveals
Planet size/radius and orbital period
Eclipse/secondary transit
Planet goes behind star causing small light drop
What eclipse data reveals
Planet temperature, emitted light
Why transit method limited
Orbit must be nearly edge-on to our view
Why transit method powerful
Can detect smaller planets than Doppler alone
Best results when transit + Doppler combined
Mass + radius + density + composition estimate
Density meaning for exoplanets
Low density likely gas giant; high density likely rocky planet
Direct imaging best for
Large hot planets far from star
Common early exoplanet bias
Large planets close to stars easier to detect
Hot Jupiter
Jupiter-mass planet orbiting very close to star
Known exoplanet orbit patterns
Many close-in orbits; many more elliptical than solar system planets
Exoplanet characteristics we can determine
Orbit size, orbital period, eccentricity, mass, size, density, temperature, composition clues
Orbital period
Length of exoplanet year
Eccentric orbit
More stretched/elliptical orbit
Massive exoplanets found early because
They create larger stellar wobble/signals
Kepler mission main method
Transit technique
51 Pegasi b importance
First confirmed exoplanet around Sun-like main-sequence star
General conclusion from discoveries
Planets are common around sta