1. Habitable Planets Astronomy 315 Professor Lee Carkner Special Topic

2. Other Earths   Are there planets in the galaxy like the Earth?  Three questions:  How do planets form?   How do we find them?

3. Solar Nebula  When the Sun was a T Tauri star, it was surrounded by the Solar Nebula   Dust clumps together to form larger and larger objects   Timescale ~ 10 million years

4. Accretion in a Protoplanetary Disk Star Disk High Density Low Density Larger Grains move to center

5. The Solar Nebula  Two basic types of dust in solar nebula:  Volatiles --  Refractory Material -- high boiling point (rock and metal)   Near the Sun the volatiles boiled off leaving only the refractory material behind  Inner solar system –  Outer solar system -- icy planetesimals

6. Forming Planets  In the outer solar system:   Core gravitationally accrete gas  Gas giants  In the inner solar system:   Terrestrial planets  In far outer solar system   Trans-Neptunian objects

7. Regions of Formation Temperature Rocky Icy Gas

8. Habitability  What kinds of planets can support life?  Gas giants?   Trans-Neptunian objects (like Pluto)?   Terrestrial planets? 

9. The Habitable Zone   In the habitable zone   Planets warm up or cool off by adding or subtracting CO 2 to atmosphere  Inner Edge --  Outer Edge -- where CO 2 clouds block sunlight  For our solar system habitable zone is about 0.95- 1.37 AU

10. Hypothetical Habitable Zone Too hot, water is destroyed Too cold, try to warm up with more CO 2 but CO 2 forms clouds and blocks sunlight Just right, temperature kept stable at 273-373 K (water is liquid)

11. Finding Exoplanets  How do you find a planet around another star?   Planets are also lost in the glare of the central star   Both objects orbit the system’s center of mass  The motion of the star is quite small, but can be detected as a slight shift in the spectral lines of the star

12. Inducing Stellar Motion

13. Light Curve of 51 Peg

14. Planetary Properties  From the period you can get the radius of the orbit   Most very small  From the velocity you can get the mass   Most very massive  Most extrasolar planets are larger than Jupiter with orbits smaller than Mercury 

15. Sample Exoplanets Data

16. Transits  A newly popular method of finding exoplanets is transit searches   The planet will block some of the starlight as it transits   By measuring the degree and length of the dimming the size and orbit of the planet can be found  Can find Earth-sized planets (from space)

17. Transit Light Curve

18. Space Interferometry  Another idea to find low mass planets is with an interferometer   A two telescope, Space Interferometry mission (SIM) may be launched in 2015 (?)   Atmosphere:  Most terrestrial planets   Earth  Oxygen and water

19. Planetary Spectra

20. Finding Earths  Planets in the habitable zone around sun-like stars will have periods of about one year  It takes several years of data to confirm them 

21. Next Time  Quiz #2  Same format as Quiz #1  Bring pencil and (real) calculator  Meet back in SC102