Airborne and groundbased spectrophotometry of comet P/Halley from 5-13 micrometers

Spectrophotometry from 5-10 micrometers (delta lambda/lambda approximately 0.02) of comet Halley was obtained from the Kuiper Airborne Observatory on 1985 December 12.1 and 1986 April 8.6 and 10.5, UT. 8-13 micrometers data were obtained on 17.2 December 1985 from the Nickel Telescope at Lick Observatory. The spectra show a strong broad emission band at 10 micrometers and a weak feature at 6.8 micrometers. We do not confirm the strong 7.5 micrometers emission feature observed by the Vega 1 spacecraft. The 10 micrometers band, identified with silicate materials, has substructure indicative of crystalline material. The band can be fitted by combining spectra data from a sample of interplanetary dust particles. The primary component of the silicate emission is due to olivine. The 6.8 micrometers emission feature can be due either to carbonates or the C-H deformation mode in organic molecules. The lack of other emission bands is used to place limits on the types of organic molecules responsible for the emission observed by others at 3.4 micrometers. Color temperatures significantly higher than the equilibrium blackbody temperature indicate that small particles are abundant in the coma. Significant spatial and temporal variations in the spectrum have been observed and show trends similar to those observed by the spacecraft and from the ground. Temporal variability of the silicate emission relative to the 5-8 micrometers continuum suggests that there are at least two physically separated components of the dust.