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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
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
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…
planets orbiting other stars3
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.

atmosphere
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

the close in extrasolar giant planets
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
atmosphere6
Atmosphere:

What is special about atomic Na and the alkali metals?

Seager & Sasselov (2000)

atmosphere7
Atmosphere:

Theoretical Transmission Spectra of HD 209458 b

Occulted Area (%)

Wavelength (nm)

Seager & Sasselov (2000)

transmission spectra
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

atmosphere9
Atmosphere:

The tricks of transmission spectroscopy:

Brown (2001)

slide10
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)

slide11

Rp

a

d

Reflected Light

Planet

planet/star flux ratio is:

Star

Earth

p is albedo

atmospheric probe
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

photometric light curves

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))
slide14

Scattered Light

  • Need to consider:
    • phase function
    • multiple scattering
slide15

Scattered Light Changes with Phase

Seager, Whitney, & Sasselov 2000

51 Peg @ 550 nm

most at a glance
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)

most at a glance17
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
lightcurve model for hd 209458b
Lightcurve Model for HD 209458b
  • Relative depths
    • transit: 2%
    • eclipse: 0.005%
  • Duration
    • 3 hours
  • Phase changes of planet

Relative Flux

Eclipse

Transit

Phase

the lightcurve from most
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
albedo results
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)

slide21

0.1 mag

0.02 mag

0.8 mmag

atmospheres
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

hd 209458b albedos
HD 209458b Albedos

New upper

limit on Ag

(Rowe et al. 2007)

Rowe et al.(2006)

models constraints
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)

direct spectrophotometry
Direct Spectrophotometry
  • Proposed NASA Mission
  • Nulling coronograph
  • Can image Jupiter-like planets in Earth-like orbits
direct spectrophotometry26
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.
more diversity than expected
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)