Extrasolar Planets.I.
1. What do we know and how do we know it.
2. Basic planetary atmospheres
3. Successful observations and future plans
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 Stars:
First ‘Super-Earth’
discovered GJ 876d:
-- Mass ~ 7.5 Earths
Also HD 69830b:
-- Mass ~ 10 Earths
NASA Kepler mission:
… Radii in this range
M = Mercury
V = Venus
E = Earth, etc.
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
• Type and size of condensate is important
• Possibly large reflected light in the optical
• Thermal emission in the infrared
Atmosphere:
What is special about atomic Na and the alkali metals?
Seager & Sasselov (2000)
Atmosphere:
Theoretical Transmission Spectra of HD 209458 b
Wavelength (nm)
Seager & Sasselov (2000)
Transmission Spectra
I   I  ,0 exp(   )
L
    n()  d
0
L
I   I  ,0 exp(   exp[ (r  R0 ) / H ]  d)
0
How large is the planet atmosphere
signal? It depends on the
atmosphere annulus / star area
H = kT/gmH scale height
 extinction cross section
L path length
Atmosphere:
The tricks of transmission spectroscopy:
Brown (2001)
The actual detection
(with the HST):
• a 5 signal
• 2x weaker than
model expected,
but within errors
• Might indicate high
clouds above
terminator
Charbonneau et al. (2002)
Reflected Light
Rp
a
planet/star flux ratio is:

Planet
Star
d

fplanet
f*
p
p is albedo
2
p
2
R
a
Earth
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
Sudarsky et al. 2000
Picture of class IV planet generated using
Celestia Software
Photometric Light Curves
Micromagnitude variability from planet phase changes
• Space-based: MOST (~2005), COROT (~2007), Kepler (~2008)
Seager et al. 2000
• D m=2.5 (Rp/D)22/3/p(sin() + (p-)cos())
Scattered Light
Need to consider:
• phase function
• multiple scattering
Scattered Light Changes with Phase
51 Peg @ 550 nm
Seager, Whitney, & Sasselov 2000
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 glance
Orbit
 circular polar orbit
 altitude h = 820 km
 period P = 101 min
 inclination i = 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
CVZ =
Continuous
Viewing
Zone
MOST
●
●
●
Relative depths
 transit: 2%
 eclipse: 0.005%
Duration
 3 hours
Phase changes of
planet
Relative Flux
Lightcurve Model for HD
209458b
Eclipse
Transit
Phase
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
●
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)
0.1 mag
0.02 mag
0.8 mmag
Atmospheres
HD 209458b is
darker than Jupiter
● Rule out class V
planet with bright
reflection silicon
clouds
●
Geometric Albedo
MOST bandpass
Marley et al. 1999
HD 209458b Albedos
New upper
limit on Ag
(Rowe et al. 2007)
Rowe et al.(2006)
Models Constraints
Different atmospheres
Equilibrium Temperature
blackbody
model
Spitzer Limit
best fit
2004 1 sigma limit – or ~2005 3 sigma limit
Rowe et al. 2006
Rowe et al. (in prep)
Direct Spectrophotometry
Proposed NASA
Mission
• Nulling coronograph
• Can image Jupiter-like
planets in Earth-like orbits
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.
Gaudi (2005) &
Charbonneau et al (2006) w
Bodenheimer et al.(2003),
Laughlin et al. (2005) models;
and Burrows et al. (2003)
More diversity than expected ?...
Some of the Hot Jupiters do not match well
models based on Jupiter & Saturn: