Spitzer Space Telescope - Directors Discretionary Time Proposal #534


CoRoT-Exo-7b: Confirming the first transiting rocky planet

Principal Investigator: Francois Fressin
           Institution: Harvard University

     Technical Contact: Francois Fressin, Harvard 

Co-Investigators: 
Suzanne Aigrain, University of Exeter
David Charbonneau, Harvard University
Malcolm Fridlund, European Space Agency
Tristan Guillot, OCA Nice
Heather Knutson, Harvard University
Tsevi Mazeh, Observatory of Tel-Aviv
Frederic Pont, University of Exeter
Heike Rauer, Berlin DLR
Guillermo Torres, Smithsonian Astrophysical Observatory

Science Category: extrasolar planets
 Observing Modes: IracMap
  Hours Approved: 20.0

Abstract:
Earlier this month CoRoT announced the discovery of a periodic photometric 
signal compatible with a 1.76 REarth planet transiting a bright (V=11.7, K=9.8) 
K0V star. If confirmed, this planet would mark the beginning of a new era in 
exoplanetary science. Unlike Hot Jupiters, low mass planets may have a much 
larger variety of compositions, resembling anything from Earth analogs to 
mini-Neptunes. Transit observations allow us to estimate the planet's radius 
that is required to distinguish between these scenarios.

In the past, transiting planet candidates have been confirmed by the detection 
of a radial velocity signal. Due to stellar activity, radial velocities from 
the HARPS spectrograph did not yield a clear measurement of the planetary mass. 
However the HARPS RVs do show a signal at the same period (0.853 days), compatible 
with a 2 to 9 Earth mass planet, although we can not entirely rule out an alternate 
scenario, in which the light curve results from the blended light of an eclipsing 
binary star system. The CoRoT team has pursued all possible ground-based follow-up 
observations, which have rejected most of these scenarios, and we have now reached 
the limits of what can be done with ground-based facilities. We propose to use 
Spitzer in channels 2 and 4 to rule out the few remaining cases. We show that the 
most likely remaining scenario would present an eclipse that is 2.5 times deeper 
in the Spitzer IRAC channel 2 than in the CoRoT bandpass. We propose to observe 
4 transits of CoRoT-Exo-7 in order to obtain an independent detection at infrared 
wavelengths and to definitely rule out these blends scenarios.