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PTYS 214 – Spring 2011

Announcements. PTYS 214 – Spring 2011. Review Guide has been uploaded to class website Review Session – Monday May 2 nd ? Thursday May 6 th ? – time?? Class website: http://www.lpl.arizona.edu/undergrad/classes/spring2011/Pierazzo_214 /

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PTYS 214 – Spring 2011

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  1. Announcements PTYS 214 – Spring 2011 • Review Guide has been uploaded to class website • Review Session – Monday May 2nd? Thursday May 6th? –time?? • Class website: http://www.lpl.arizona.edu/undergrad/classes/spring2011/Pierazzo_214/ • Useful Reading:class website  “Reading Material” http://en.wikipedia.org/wiki/Extrasolar_planet http://exoplanet.eu/catalog.php http://www.solstation.com/stars/gl581.htm

  2. Planetary Sciences Graduate Teaching Assistant Excellence Award • Planetary Science Department initiative to promote, recognize and reward exemplary performance among graduate teaching assistants assigned to PTYS undergraduate courses • If you think your PTYS-214 Teaching Assistant qualifies for the award, please fill out a nomination form describing: • Why you are nominating the TA • How the TA has contributed to your learning experience • Nomination forms and the drop box are located on the table outside your classroom, room 308 • The Teaching Assistants for PTYS214-2 are: • LissaOng & Devin Schrader

  3. Extrasolar Planets Also called exoplanets, they are planets that orbit other stars beyond our Sun The existence of other solar systems has been suspected for centuries, but verified only in the 1990s

  4. Detecting Extra-Solar Planets • Problem #1:Planets are not bright objects! • Problem #2:Planets are relatively small and close to a • bright star • (DSun~10 DJupiter~100 DEarth) • Successful detection techniques: • Stellar Radial Velocity, or Doppler Method • Planetary Transit • Direct Imaging • Gravitational microlensing

  5. Radial Velocity Technique Most exoplanets (>300) are detected by radial velocity technique Uses the Doppler Effect to measure changes in the radial velocity of a star caused by the small gravitational force of an unseen orbiting planet ….but it can only measure motion along the line of sight (edge on) Allows to determine the planet’s mass plus shape and size of orbit

  6. Radial Velocity Technique • Observe red-shifting and blue-shifting of the star’s spectral lines caused by Doppler effect • Amount of blue or red shift corresponds to the star’s radial velocity towards or away from us

  7. Planetary Transit Technique Measures dimming of star light as planet passes in front of star Star-light may dim by only 0.000001 (10-6) Over 50 planets have been detected by the transit technique

  8. Planetary Transit Technique Advantages: a) Relatively cheap b) Can determine the size of the planet Disadvantages: a) Bias towards large planets and in short period orbits b) False detections due to stellar variability c) Planet’s orbit must be seen edge-on from the observer point of view (so the planet passes in front of the star)

  9. Direct Imaging Direct detection of planets is extremely difficult Rare cases when direct imaging can work are: Planet is very large (considerably larger than Jupiter) Planet is widely separated from its parent star Planet is young (so that it is hot and emits intense infrared radiation) Few exoplanets are imaged directly 2005; European Southern Observ. Image of a planet around GQ Lupi (early K-type star) The planet is believed to be about twice the mass of Jupiter and to have an orbital radius of about 30 AU (similar to Neptune)

  10. Gravitational Microlensing Use the gravitational effect of large objects that can bend light around them If the object is a star with a planet, the planet can be detected by its effect on the microlensing Less than 10 potential exoplanets detected by this technique

  11. Hertzsprung-Russell (HR) Diagram

  12. Stellar Habitable Zone

  13. Habitable Planets around M dwarf stars • Much less massive than Sun-like stars (G-type stars) • Deeper transits, better RV detection • Very low luminosity  Smaller HZs • Consider an M5 dwarf which has a luminosity • L = 0.0055 x L(solar) • [Recall L(Solar) = 3.84 x 1026 W]. • At what distance (D) from the M5 dwarf would a • planet receive the same total radiation flux of the • Earth? [Recall S0 = 1370 W/m2]

  14. So why looking at M dwarf stars? • More numerous than Sun-like stars • Constitute 20 of the 30 stars nearest to Earth • Much longer life spans than Sun-like stars • Some can live for trillions of years!

  15. Problems with M-dwarfs • Limited Habitable Zone (too cold?) • Tidal locking (only one face of planet facing star, • becomes synchronously rotating) • Stellar variability: lots of flares • HOWEVER: • A study by Joshi et al. 1997 has shown that • atmospheric circulation should help reduce day-night • temperature variations. • Heath et al. 1999 concluded that even during a flare, • radiation received by a planet in the HZ of an M dwarf • is comparable to that received by the Earth. • These planets could still be habitable!

  16. Modeling the habitability of Earth-like exoplanets Use atmospheric circulation models – General Circulation Models (GCMs) GCMs for hot Jupiters are much less complicated than terrestrial GCMs Why? Terrestrial GCMs must consider: • Varying atmospheric compositions • Climate feedback systems!

  17. MEarth Project • Ground-based 2 year survey of ~2000 nearby M dwarfs with masses ~1/3 mass of Sun • Smaller M dwarfs — bigger transits, less noise • Probability to find planets in HZ is only 10%, but the survey produced the discovery of super-Earth GJ1214b!

  18. Observations from Space Avoid distortion introduced by Earth’s atmosphere and provide for much more precise measurements • ESA’s CoRoT (a French-European Space Agency mission) uses the transit method to detect planets around the size of Earth It detected its first extrasolar planet in May 2007! • NASA’s Kepler Space Observatory was launched in March 2009 (similar to CoRoT)

  19. Advantage of avoiding Earth’s atmosphere From the ground From space

  20. NASA’s S(pace) I(nterferometry) M(ission) Lite Currently under development, it will measure the wobble of stars against other stars in the background using optical interferometry (combining light from two or more telescopes) SIM PlanetQuest will determine the positions of stars several hundred times more accurately than anything previously possible, helping to pin-point Earth-sized planets

  21. Other exoplanet searches • HARPS (High Accuracy Radial Velocity Planet Searcher) • TPF (Terrestrial Planet Finder) • JWST (James Webb Space Telescope) • Darwin • TrES (Transatlantic Exoplanet Survey)

  22. Detection Limits Planet closest to Earth-size, discovered so far: • Planet around 2 Earth masses (Gliese 581e) From Gaidos et al., Science (2007)

  23. How Do 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…

  24. An Encouraging Experiment…

  25. Galileo data in the Near-IR Simultaneous presence of O2 or O3 and a reduced gas (CH4 or N2O) is the best evidence for life *Credit Joshua Lederburgand James Lovelock for the idea (1964)

  26. Thermal IR spectra Source: R. Hanel, Goddard Space Flight Center

  27. Quiz Time !

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