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Extrasolar Planets.I.

Extrasolar Planets.I. What do we know and how do we know it. Basic planetary atmospheres Successful observations and future plans. Planets Orbiting Other Stars. Total: 209 discovered to-date. Statistics: Gas giant planets, like Jupiter & Saturn,

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Extrasolar Planets.I.

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  1. Extrasolar Planets.I. What do we know and how do we know it. Basic planetary atmospheres Successful observations and future plans

  2. Planets Orbiting Other Stars • Total: 209 discovered to-date. • Statistics: • Gas giant planets, like Jupiter & Saturn, exist around >12% of stars (Marcy et al. 2005); • Lower-mass planets (Super-Earths, 3 known to-date) are significantly more common (Rivera et al. 2005; Beaulieu et al. 2006). • No Earth-like planets yet…

  3. Planets Orbiting Other Stars: First ‘Super-Earth’ discovered GJ 876d: -- Mass ~ 7.5 Earths Also HD 69830b: -- Mass ~ 10 Earths NASA Kepler mission: … Radii in this range after Gould et al. (2006) M = Mercury V = Venus E = Earth, etc.

  4. Atmosphere: • In general - outer boundary for planet’s thermal evolution - the extrasolar planets have introduced conditions never imagined • Clouds & (photo)chemistry • Evaporation (very hot & hot Jupiters) Transits allow spectroscopic studies of the planet’s atmosphere

  5. The Close-in Extrasolar Giant Planets Seager & Sasselov 2000 • Type and size of condensate is important • Possibly large reflected light in the optical • Thermal emission in the infrared

  6. Atmosphere: What is special about atomic Na and the alkali metals? Seager & Sasselov (2000)

  7. Atmosphere: Theoretical Transmission Spectra of HD 209458 b Occulted Area (%) Wavelength (nm) Seager & Sasselov (2000)

  8. Transmission Spectra How large is the planet atmosphere signal? It depends on the atmosphere annulus / star area H = kT/gmHscale height sl extinction cross section L path length

  9. Atmosphere: The tricks of transmission spectroscopy: Brown (2001)

  10. The actual detection (with the HST): • a 5s signal • 2x weaker than model expected, but within errors • Might indicate high clouds above terminator Charbonneau et al. (2002)

  11. Rp  a d Reflected Light Planet planet/star flux ratio is: Star Earth p is albedo

  12. Atmospheric Probe • Sudarsky Planet types • I : Ammonia Clouds • II : Water Clouds • III : Clear • IV : Alkali Metal • V : Silicate Clouds • Predicted Albedos: • IV : 0.03 • V : 0.50 Picture of class IV planet generated using Celestia Software Sudarsky et al. 2000

  13. Micromagnitude variability from planet phase changes • Space-based: MOST(~2005), COROT (~2007), Kepler (~2008) Photometric Light Curves Seager et al. 2000 • D m=2.5 (Rp/D)22/3/p(sin(a) + (p-a)cos(a))

  14. Scattered Light • Need to consider: • phase function • multiple scattering

  15. Scattered Light Changes with Phase Seager, Whitney, & Sasselov 2000 51 Peg @ 550 nm

  16. MOST at a glance Mission • Microvariability and Oscillations of STars / Microvariabilité et Oscillations STellaire • First space satellite dedicated to stellar seismology • Small optical telescope & ultraprecise photometer • goal: ~ few ppm = few micromag Canadian Space Agency (CSA)

  17. MOST at a glance MOST CVZ = Continuous Viewing Zone orbit normal vector to Sun Orbit • circular polar orbit • altitudeh = 820 km • periodP = 101 min • inclinationi = 98.6º • Sun-synchronous • stays over terminator • CVZ ~ 54° wide • -18º < Decl. < +36º • stars visible for up to 8 wks • Ground station network • Toronto, Vancouver, Vienna

  18. Lightcurve Model for HD 209458b • Relative depths • transit: 2% • eclipse: 0.005% • Duration • 3 hours • Phase changes of planet Relative Flux Eclipse Transit Phase

  19. The Lightcurve from MOST 2005 observations, 40 minute binned data 0.03 mag 45 days • 2004 data : 14 days, 4 orbital cycles • 2005 data : 45 days, 12 orbital cycles • duty cycle : ~90% • 473 896 observations • 3 mmag point-to-point precision

  20. Albedo Results • Best fit parameters: • Albedo : 0.07 ± 0.05 • stellar radius : 1.346 ± 0.005 RJup • Other Parameters: • stellar mass: 1.101 Msun • inclination: 86.929 • period : 3.52... days see Knutson et al. 2006 1,2,3 sigma error contours Radius (Jupiter) Geometric Albedo Rowe et al. (in prep)

  21. 0.1 mag 0.02 mag 0.8 mmag

  22. Atmospheres MOST bandpass • HD 209458b is darker than Jupiter • Rule out class V planet with bright reflection silicon clouds Geometric Albedo Marley et al. 1999

  23. HD 209458b Albedos New upper limit on Ag (Rowe et al. 2007) Rowe et al.(2006)

  24. Models Constraints Different atmospheres blackbody model Equilibrium Temperature Spitzer Limit best fit 2004 1 sigma limit – or - ~2005 3 sigma limit Rowe et al. 2006 Rowe et al. (in prep)

  25. Direct Spectrophotometry • Proposed NASA Mission • Nulling coronograph • Can image Jupiter-like planets in Earth-like orbits

  26. Direct Spectrophotometry • Could observe changing cloud cover and atmospheric conditions on gas giant planets with highly eccentric orbits, like HD 168443. • Very exciting unique opportunity to study rates for photochemistry & forcing.

  27. More diversity than expected ?... Some of the Hot Jupiters do not match well models based on Jupiter & Saturn: Gaudi (2005) & Charbonneau et al (2006) w Bodenheimer et al.(2003), Laughlin et al. (2005) models; and Burrows et al. (2003)

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