Exoplanets
Worlds Without End
Copyright Lynette Cook, used with permission
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Goals
• Are there planets around other stars?
• How do we know?
• Are they systems like ours?
Copyright Lynette Cook, used with permission
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Are there other Earths?
Copyright – Tyler Nordgren
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Putting it all together
Copyright Lynette Cook, used with permission
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1. Thermal Emission and Spectral lines
• A star like our Sun has absorption lines.
HOT
You
COOL
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2. Reflex Motion
• The Moon doesn’t orbit the Earth.
• The Earth doesn’t orbit the Sun.
• What do they do?
• They each orbit their combined center of mass.
X
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The “Wobble”
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3. Doppler Shifts
• Movement towards or away yields Doppler shifts.
X
http://www.howstuffworks.com/planet-hunting2.htm
You
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4. Doppler Velocity
• From Doppler shifts we get a velocity and period.
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5. Kepler
• Kepler’s Second Law:
• Kepler’s Third Law:
a( AU )
P( yrs) 
M*
3
2
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Copyright Lynette Cook, used with permission
Result: 51 Pegasi
a = 0.052 AU
Mayor and Queloz
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Concept Test
•
We know of planets around other stars because:
a. We have seen the changing velocity of a star caused
by the pull of a small unseen planet.
b. We have seen the motion of the planet caused by the
wobble of the star.
c. We have seen the changing position of the star caused
by the pull of the small unseen planet.
d. We have seen the changing velocity of the planet
caused by the motion of the star.
e. We have seen the planet reflecting the star’s light.
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Worlds without End?
• Known Planets:
– In our Solar System: 9
– Outside our Solar System: 206
• Known Planetary
Systems:
– Prior Sept. 1995: 1 (ours)
– As of Sept. 2004: 21
Copyright Lynette Cook, used with permission
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Upsilon Andromedae
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But Are They Real?
Copyright Lynette Cook, used with permission
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Planet Shadows
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HD 209458
Based on Doppler curve,
knew when planet might
pass in front of its star.
Greg Henry (Tennessee State Univ.)
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Copyright Lynette Cook, used with permission
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Hubble Space
Telescope
Savage et al. 2001
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Hot Jupiters
Atmosphere evaporation
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Homework #10
• For Friday 26-Sept: Read B13.1-13.2.
• Do: Problems 20, 25, 34, 52,57
• Don’t forget Topic of Confusion
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