Spitzer Space Telescope - General Observer Proposal #80082


Observations of Carbon Dioxide in the Coma of Comet C/2009 P1 Garradd

Principal Investigator: Adam McKay
           Institution: New Mexico State University

     Technical Contact: Adam McKay, New Mexico State University

Co-Investigators: 
William Reach, NASA Ames                                              
Michael Kelley, University of Maryland                                
Michael DiSanti, Goddard Space Flight Center                          
Nancy Chanover, New Mexico State University                           

Science Category: comets 
 Observing Modes: IRAC Post-Cryo Mapping
  Hours Approved: 8.6 

Abstract:
The study of cometary composition is important to understanding the formation
and evolution of our solar system. Comets have undergone very little thermal
evolution in their lifetimes, which results in their near pristine composition.
The nucleus of a comet is very rarely detected directly. Instead, we observe the
coma that surrounds the nucleus. Physical and chemical processes in the coma
affect its composition, and therefore coma composition is not a direct
representation of nuclear composition. An important trend is the observed
variation of coma composition with heliocentric distance, most likely influenced
by the volatility of the main surface ices, H2O, CO2, and CO. Infrared studies
of these molecules are complicated by telluric features, so often daughter
molecules of these species such as OH are observed instead. A potentially
effective tracer for these primary ices is atomic oxygen in the coma. However,
the relationship between these ices and atomic oxygen is only understood at a
qualitative level. We propose to use Spitzer observations in IRAC's 4.5 micron
band pass to observe the CO2 v3 band at 4.26 microns in comet C/2009 P1 Garradd.
These observations will be coordinated with observations of atomic oxygen
obtained at Apache Point Observatory and observations of H2O at NASA's Infrared
Telescope Facility (IRTF). These near simultaneous observations of H2O, CO2, and
atomic oxygen in a cometary coma will increase our understanding of the link
between these primary ices and atomic oxygen. With a complete understanding of
the relationship between atomic oxygen and the primary ices on the nucleus,
observations of atomic oxygen can serve as a powerful proxy for the production
of these primary volatiles and aid our understanding of the variation in coma
composition as a function of heliocentric distance, and therefore the
composition of the nucleus and how our solar system was formed.