1. Homework 8 Due: Monday, Nov. 28, 9:00 pm, Exam 2: Weds., Nov. 30

2. Remember: attendance is mandatory next week.

3. Searching for Exoplanets… What have we found?

4. As of November 27, 2011, 704 extrasolar planets have been detected and confirmed (increase of 200 in one year). The Kepler spacecraft has discovered over 1200 candidate objects; estimates are that ~ 50% of these are planets. Discovery techniquePlanets Radial velocity650 Astrometry4 Microlensing13 Imaging29 Transit186 http://exoplanet.eu/ Note that some exoplanets have been discovered/confirmed uasing multiple methods

5. Keep in mind that we are exploring only the nearby neighborhood. would be the size of the United States. Our Milky Way Galaxy where we’ve found new planets would only be the size of Manhattan. And the neighborhood Our whole Solar System would be this big if you shrunk our solar system to the size of a quarter:

6. Extrasolar Planets The rate of discovery is increasing rapidly.

7. Extrasolar Planets Most orbit stars with masses similar to or less than the Sun. http://exoplanet.eu/

8. Extrasolar Planets Most of these planets have masses similar to, or somewhat less than, the Jovian planets. http://exoplanet.eu/ M Earth (x-axis is logarithmic)

9. Extrasolar Planets Most of these planets are close to their central star. http://exoplanet.eu/ Note: x-axis is logarithmic

10. Extrasolar Planets Most have short periods. These are most easily found. http://exoplanet.eu/ Note: x-axis is logarithmic

11. Results consistent with at least 40% of Sun- like stars having at least one low-mass planet. The majority of planets with masses greater than Neptune appear to reside in systems with multiple planets.

12. If the results to date are typical, then there are ~ 15,000,000,000 low mass planets in Milky Way! ~ 3,000,000,000,000,000,000,000 in Universe!

13. If the goal is to find planets with evidence of life, most of those discovered so far are not good candidates.

14. 17 Most are gas giants like Jupiter or Saturn and in the wrong location. The right location in our solar system (habitable zone).

15. Most of them have highly elliptical orbits, or are too close to their parent stars. Many of the new planets get too hot or too cold to support life. Too hot! Too cold!Just right!

16. Kepler and other planned missions will change of of this. Too hot! Too cold!Just right!

17. Habitable Zone Planets 464 known as of November 27, 2011 http://www.hzgallery.org

18. Habitable Zone Planets http://www.hzgallery.org

19. Habitable Zone Planets Known exoplanets that spend at least a portion of their orbit in the Habitable Zone (464 total). Size of points represents the fraction of time spent in the HZ – largest points are planets that reside full time in the HZ. http://www.hzgallery.org

20. “Super-Earths” An extrasolar planet that is somewhat more massive than the Earth but less than ~ 10 Earth masses: ~20 known. Kepler-10b

22. Gliese 581 g  Mass ~ 3 - 4 Earth Masses  Radius ~ 1.5 x Earth  In habitable zone  May have liquid water on surface  Orbits a red dwarf  Period = 37 days  May have magnetosphere  Needs confirming observations  Probably tidally locked  LIFE?

23. How will we know if a planet can support life? Look for evidence of oxygen Look for liquid water Analyze the reflected light from the planet to see if the planet has an atmosphere Look for signs of biological activity (methane) and rule out other explanations. 17

24. 19 Now the hunt for Earth-like planets really blasts off… …on the ground and in space. Keck Interferometer Spitzer Space Telescope SIM PlanetQuest Kepler Large Binocular Telescope Interferometer Terrestrial Planet Finders

25. We shall not cease from exploration And the end of all our exploring Will be to arrive where we started And know the place for the first time. T.S. Eliot Four Quartets

26. Group Activity Organize your groups in the usual manner.

27. Life on a synchronously rotating planet Planets in the Habitable Zone of M stars are likely to rotate synchronously with their orbit. Computer simulations suggest that on a synchronously rotating planet with a thick atmosphere, winds will carry heat from the side constantly facing the star to the back, dark side. If this is correct, there would be a ring-like zone between the light and dark halves of the planet that might be habitable.

28. Life on a synchronously rotating planet What kind of adaptations would you expect for life in this zone? Explain. Speculate on what life might be like on such a planet. Let your imagination run free!