Infrared Spectra of Comets as a Barometer for Their Evolution

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We have found that the fractal dimension of aggregated dust particles in comets determines the strength of peaks characteristic of olivine detected in the infrared spectra of dust in cometary comae, while the volume fraction and carbonization of organic refractory material in the dust aggregates play an important role in the determination of the peak wavelengths. Furthermore, both an increase in the fractal dimension and the carbonization of organic refractory material are associated with the formation of a dust mantle on the surface of a comet. Therefore, the infrared spectra of cometary comae can be regarded as a barometer of the evolution of comets as well as the alteration of comet grain properties. Since the processing of comet dust proceeds with the orbit of the parent-body comet, we expect that a thorough analysis of infrared data will reveal a correlation between the spectral features characteristic of olivine and the orbital semi-major axes of comets.