Spitzer Space Telescope - General Observer Proposal #50650


The Temperatures of Large Dust Grains emitted from 67P/Churyumov-Gerasimenko

Principal Investigator: Jessica Agarwal
           Institution: ESTEC, European Space Agency

     Technical Contact: Jessica Agarwal, ESTEC, European Space Agency

Co-Investigators: 
Eberhard Gruen, LASP, Boulder                                         
William Reach, IPAC/SSC/Caltech                                       
John Stansberry, Steward Observatory, Tucson                          
Mark Sykes, Planetary Science Institute, Tucson                       

Science Category: comets 
 Observing Modes: MipsPhot 
  Hours Approved: 13.5 

Abstract:
We propose to observe the coma and specific sections of the dust trail of
Rosetta target comet 67P/Churyumov-Gerasimenko (CG) using MIPS Photometry mode
at 24 and 70 micron under two different viewing geometries (visibility windows
in June/July 2008 and November 2008 to January 2009). Dust trails consist of
mm-cm sized particles that trace out a portion of their parent comet's orbit and
comprise a record of the continuous history of emission of these large
particles. The proposed observations will extend earlier Spitzer programs on the
CG dust trail (PIDs 210 and 20235) to the 70 micron range, rendering the first
two-colour data of a cometary dust trail since IRAS. They will also provide the
first mid-infrared images of the coma and young tail of comet CG. They will
allow us to derive the temperature of the trail particles under two different
insolation angles and thereby to probe if these particles are able to sustain a
temperature gradient, which will provide information on their porosity and heat
conductivity. The measured surface brightness of the trail as a function of
distance from the nucleus and time will - together with the temperature
information - allow us to refine our existing models of the emission history and
dynamical properties (sensitivity to radiation pressure) of the grains. The
modelling results will be used to predict the large particle environment that
Rosetta will face on approach to the comet and during operations. Complementary
to modelling of the dust trail, the production of large particles will be
directly observable in the developing coma of the comet that during Cycle 5
approaches its perihelion in February 2009.