Spitzer Space Telescope - Directors Discretionary Time Proposal #261


Thermal Emission from the Newest, Closest, and Brightest Transiting
Planet

Principal Investigator: David Charbonneau
           Institution: Harvard

Co-Investigators: 
Lori Allen, SAO                                                       
Travis Barman, UCLA                                                   
Francois Bouchy, Astrophysical Laboratory of Marseille                
Timothy Brown, High Altitude Obs. NCAR                                
Michel Mayor, Geneva Obs.                                             
Tom Megeath, SAO                                                      
Claire Moutou, Astrophysical Laboratory of Marseille                  
Didier Queloz, Geneva Obs.                                            
Stephane Udry, Geneva Obs.                                            

Science Category: extrasolar planets 
 Observing Modes: IracMap MipsPhot 
  Hours Approved: 10.1 

Abstract:
We propose to observe the newly-discovered transiting-planet system HD
189733 during two times of secondary eclipse, corresponding to the
passage of the planet behind the star.  Of the 4 known transiting
planets accessible to Spitzer, this object offers by far the greatest
signal-to-noise ratio, owing to both the apparent brightness of the
system and the favorable ratio of the planetary flux to that of the
star.  By measuring the planetary flux in 5 band passes (3.6, 4.5,
5.8, 8.0, & 24 um), we will directly constrain models of the planetary
emission, which in turn should allow identification of the molecules
that dominate its spectrum.  Moreover, high-cadence observations with
IRAC during times of ingress and egress may permit us to spatially
resolve the planetary emission over the surface of the planet,
providing an unprecedented probe of the dynamics of these strongly
irradiated exoplanet atmospheres.  These observations will firmly
establish Spitzer as the primary observatory in the nascent field of
comparative exoplanetology.