The dust coma of Comet P/Giacobini-Zinner in the infrared

Area of Science:

• Astronomy and Astrophysics
• Cometary Science
• Infrared Astronomy

Background:

• Short-period comets offer insights into early solar system materials.
• Understanding cometary dust composition is crucial for planetary formation studies.
• Previous studies on Comet Halley provide a benchmark for dust properties.

Purpose of the Study:

• To present and analyze infrared photometry of Comet P/Giacobini-Zinner.
• To investigate the dust properties and composition of the comet's inner coma.
• To compare the dust characteristics of P/Giacobini-Zinner with those of Comet Halley.

Main Methods:

• 1-20 micrometer photometry was conducted using the NASA Infrared Telescope Facility.
• Observations spanned from June to September 1985, covering a heliocentric distance range of 1.57-1.03 AU.
• Spectral analysis focused on identifying silicate emission features and fitting thermal emission continua.

Main Results:

• A weak, broad 10 micrometer silicate emission feature was detected on August 26.
• The total dust cross section was significantly lower than Comet Halley's, by factors of 10-100.
• Dust production rates near perihelion were estimated between 10^5 to 10^6 g/s.
• A heterogeneous grain model with excess large particles best fit the observed spectrum.

Conclusions:

• The presence of weak or absent silicate emission does not preclude silicates in cometary dust.
• Comet P/Giacobini-Zinner likely had a lower abundance of silicate particles with radii <= 1 micrometer compared to Comet Halley.
• The dust/gas mass ratio on August 26 was estimated to be approximately 0.1-1.