Spitzer Space Telescope - Archive Research Proposal #40571


Mining the Deep Impact Spitzer Archive for Crystalline Silicates

Principal Investigator: Diane Wooden
           Institution: NASA Ames Research Center

     Technical Contact: Diane Wooden, NASA Ames Research Center

Co-Investigators: 
David Harker, University of California, San Diego                     
Charles Woodward, University of Minnesota                             
Mike Kelley, University of Central Florida                            

Science Category: Comets 
Dollars Approved: 86378 

Abstract:
The Deep Impact Mission hit comet Jupiter Family 9P/Tempel 1 on 2005 July 4 and
expelled surface and subsurface nuclear materials into its coma. To our
surprise, the dust grains and the volatile gases were more similar in
composition and abundance to Oort cloud (long-period) comet Hale-Bopp than to
any previously observed Jupiter Family (short-period) comet. Crystalline
silicate features are much more pronounced in the Deep Impact-induced coma
compared to the normal coma. We propose to investigate whether the silicate
feature and the crystalline silicate features are stronger because the grain
structure is different (e.g., more porous), or whether the grains are of
different composition. If the subsurface and surface grains are of different
composition, this has implications for the `aging' of Jupiter Family comets in
the inner solar system or implies the nucleus is inhomogeneous on even smaller
scales than suggested by the TALPS model (Belton et al. 2007). Our program will
utilize the Spitzer (+IRS) archive data obtained over a 164 hr duration, as well
as observations of the pre-impact coma and the coma weeks after impact. The Deep
Impact Spitzer data set is of unparalleled signal-to-noise: the 10''-wide IRS
slit samples the low-surface brightness pre-impact coma and reveals crystalline
silicate emission features that are not discernible in 8-m class telescope
spectra of the inner coma.