1. Extra-Solar Planets Astronomy 311 Professor Lee Carkner Lecture 24

2. Nelson Lecture Tomorrow Night  7:30 pm, Hanson 102  Dr. Jason Steffen  “Finding Other Earths”  See me to sign in for extra credit

3. Finding Exoplanets   Planets are much too faint to be seen with a telescope   As the planet orbits the star, the star also orbits the planet   The motion of the star is quite small, but can be detected as a slight shift in the spectral lines of the star

4. Finding Exoplanets

5. The Doppler Effect  When you observe a moving object, the wavelengths of light you observe change  Moving away --  Moving towards --  Example: the change in a car’s sound as it moves past you   By measuring the shift of lines in a spectrum, you can determine how fast the object is moving

6. Doppler Effect

7. Searching For Exoplanets   Measurements are made over a long period of time and plotted   As the planet moves around in its orbit, the velocity of the star should go from positive to zero to negative and back to positive again   We find exoplanets by noticing changes in the spectral lines that indicate a planet tugging on the star

8. Orbits of a Star+Planet System Star Planet Center of Mass V star V planet

9. Light Curve of 51 Peg

10. Transits   For orbits seen edge on, the planet passes in front of the star once per orbit   We can measure and time this slight dimming with CCD cameras  By measuring the degree and length of the dimming the size and orbit of the planet can be found  Can find Earth-sized planets

11. Transit Light Curve

12. Planetary Properties   Use Kepler’s 3rd Law (P 2 =a 3 )   Larger planets produce a larger velocity   Large velocities and short periods are easier to measure

13. What is a Planet?  Star --  Mass > 0.08 M Sun (84 M Jupiter )  Brown Dwarf --  Mass > 10 M Jupiter  Planet --  Mass < 10 M Jupiter  Planets and brown dwarfs can be hard to tell apart

14. Known Exoplanets   More are being discovered all the time  Masses range from  Orbits range from  Searches are biased towards large planets in tight orbits

15. Exoplanet Orbits   Most systems have only one known planet but we are starting to find more   Long term observations are needed to see the longer periods  Most orbits are elliptical  Are the nearly circular orbits of our solar system atypical?

16. Velocity Plots for Upsilon And System

17. Orbits in Upsilon And System

18. A Multiple Exoplanet System

19. Orbit Evolution   It should be too hot close to the star to form giant planets (no icy planetesimals)   The best theory holds that large planets form in the outer protoplanetary disk and then move inward due to friction in the disk  The magnetic field of the star may produce a “hole” in the inner disk, stopping the motion before the planet hits the star

20. Exoplanets and Habitability  Are any of the new planets habitable?  No,   They are almost all gas giants with no surface  However,   Example: 47 UMa, R orbit =2.1 AU   The velocities they produce are too small to measured via Doppler shift

21. Planetary Spectra

22. Space Interferometry   Combine the images from many small telescopes to produce the effect of a large telescope   Others with more and larger telescopes may follow  Would be able to detect the movement of a star in the sky as it is being pulled by its planets (astrometry) 

23. Next Time  Read Chapter 16

24. Summary  Recently many planets around other stars have been found  The planets are detected by measuring the motions they induce in the central star  The period and velocity of the motions allows the determination of the mass and orbit of the planet  New missions in the next 20 years will allow for the detection of many new planets, including Earth-like, habitable ones

25. Summary: Exoplanet Properties  Most known exoplanets are large (~M Jupiter ) and in close orbits  They may form further out and then move in  A few are near the habitable zone  We are starting to find additional planets in the systems