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:

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First ‘Super-Earth’ discovered GJ 876d:-- Mass ~ 7.5 Earths

Also HD 69830b:-- Mass ~ 10 Earths

NASA Kepler mission:

… Radii in this range

M = MercuryV = VenusE = 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

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Atmosphere:What is special about atomic Na and the alkali metals?

Seager & Sasselov (2000)

Atmosphere:

Theoretical Transmission Spectra of HD 209458 b

Wavelength (nm)

Occ

ulte

d A

rea

(%)

Seager & Sasselov (2000)

Transmission Spectra

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L

dHRrII

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ll

λλλ

λλ

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σ

στ

τ

H = kT/gmH scale height extinction cross section L path length

How large is the planet atmospheresignal? It depends on theatmosphere annulus / star area

Atmosphere:The tricks of transmission spectroscopy:

Brown (2001)

The actual detection (with the HST):

• a 5signal• 2x weaker than

model expected, but within errors

• Might indicate high clouds above terminator

Charbonneau et al. (2002)

planet/star flux ratio is: a

d

Rp

StarPlanet

Earth

ε ≡fplanet

f*

= pRp

2

a2

Reflected Light

p is albedo

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)

• m=2.5 (Rp/D)22/3/(sin() + (-)cos())

Seager et al. 2000

Scattered Light

Need to consider:• phase function• multiple scattering

Scattered Light Changes with Phase

Seager, Whitney, & Sasselov 200051 Peg @ 550 nm

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

MOST at a glance

Canadian Space Agency (CSA)

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

MOST at a glance

MOST

orbit normal vector

to Sun

CVZ = Continuous Viewing Zone

Orbit

Lightcurve Model for HD 209458b

● Relative depths transit: 2% eclipse: 0.005%

● Duration 3 hours

● Phase changes of planet

Phase

Rela

tive F

lux

Eclipse Transit

The Lightcurve from MOST

45 days

0.03 mag

● 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

2005 observations, 40 minute binned data

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

Geometric Albedo

Radiu

s (J

upit

er)

1,2,3 sigmaerror contours

Rowe et al. (in prep)

0.1 mag

0.02 mag

0.8 mmag

Atmospheres

MOST bandpass

Geom

etr

ic A

lbed

o● HD 209458b is darker than Jupiter● Rule out class V planet with bright reflection silicon clouds

Marley et al. 1999

HD 209458b AlbedosHD 209458b Albedos

New upperlimit on Ag

Rowe et al.(2006)(Rowe et al. 2007)

Models Constraints

2004 1 sigma limit – or - ~2005 3 sigma limit

Spitzer Limit

Different atmospheres

blackbody

model

Rowe et al. 2006Rowe et al. (in prep)

best fit

Equili

bri

um

Tem

pera

ture

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.

Some of the Hot Jupiters do not match wellmodels based on Jupiter & Saturn:

More diversity than expected ?...

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