INFRARED SPECTROSCOPY OF COMET 73P/SCHWASSMANN-WACHMANN 3 USING THE SPITZER SPACE TELESCOPE
- Space Science Institute, Boulder, CO 80301 (United States)
- Applied Physics Lab, Johns Hopkins University, Laurel, MD 20723 (United States)
- Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
- Department of Physics and Astronomy, University of Wisconsin, Eau Claire, WI 54702 (United States)
- Aerospace Corporation, Los Angeles, CA 90009 (United States)
- Department of Physics, University of Cincinnati, Cincinnati, OH 45221 (United States)
We have used the Spitzer Space Telescope Infrared Spectrograph (IRS) to observe the 5-37 {mu}m thermal emission of comet 73P/Schwassmann-Wachmann 3 (SW3), components B and C. We obtained low spectral resolution (R {approx} 100) data over the entire wavelength interval, along with images at 16 and 22 {mu}m. These observations provided an unprecedented opportunity to study nearly pristine material from the surface and what was until recently the interior of an ecliptic comet-the cometary surface having experienced only two prior perihelion passages, and including material that was totally fresh. The spectra were modeled using a variety of mineral types including both amorphous and crystalline components. We find that the degree of silicate crystallinity, {approx}35%, is somewhat lower than most other comets with strong emission features, while its abundance of amorphous carbon is higher. Both suggest that SW3 is among the most chemically primitive solar system objects yet studied in detail, and that it formed earlier or farther from the Sun than the bulk of the comets studied so far. The similar dust compositions of the two fragments suggest that these are not mineralogically heterogeneous, but rather uniform throughout their volumes. The best-fit particle size distribution for SW3B has a form dn/da {approx} a{sup -3.5}, close to that expected for dust in collisional equilibrium, while that for SW3C has dn/da {approx} a{sup -4.0}, as seen mostly in active comets with strong directed jets, such as C/1995 O1 Hale-Bopp. The total mass of dust in the comae plus nearby tail, extrapolated from the field of view of the IRS peak-up image arrays, is (3-5) x 10{sup 8} kg for B and (7-9) x 10{sup 8} kg for C. Atomic abundances derived from the spectral models indicate a depletion of O compared to solar photospheric values, despite the inclusion of water ice and gas in the models. Atomic C may be solar or slightly sub-solar, but its abundance is complicated by the potential contribution of spectrally featureless mineral species to the portion of the spectra most sensitive to the derivation of the C abundance. We find a relatively high bolometric albedo, {approx}0.13 for the dust, considering the large amount of dark carbonaceous material, but consistent with the presence of abundant small particles and strong emission features.
- OSTI ID:
- 21582926
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Vol. 142, Issue 3; Other Information: DOI: 10.1088/0004-6256/142/3/80; ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ABSORPTION SPECTROSCOPY
ABUNDANCE
ALBEDO
ASTROPHYSICS
BOLOMETERS
CARBON
CARBONACEOUS MATERIALS
COMETS
DATA ANALYSIS
DUSTS
ICE
INFRARED SPECTRA
SILICATES
SOLAR SYSTEM
SUN
TELESCOPES
ELEMENTS
MAIN SEQUENCE STARS
MATERIALS
MEASURING INSTRUMENTS
NONMETALS
OXYGEN COMPOUNDS
PHYSICS
SILICON COMPOUNDS
SPECTRA
SPECTROSCOPY
STARS