Mid-infrared spectroscopic observations of comet 17P/Holmes immediately after its great outburst in October 2007

TL;DR

This study uses mid-infrared spectroscopy to analyze the mineral composition of comet 17P/Holmes after its 2007 outburst, revealing a significant crystalline silicate presence and suggesting formation via non-equilibrium condensation in the solar nebula.

Contribution

It provides the first detailed mineral abundance analysis of comet 17P/Holmes using thermal emission modeling of mid-infrared spectra, offering insights into its formation process.

Findings

Crystalline silicate mass fraction is approximately 0.31.

Olivine-to-pyroxene ratio is about 1.20.

Mineral formation consistent with non-equilibrium condensation in the solar nebula.

Abstract

Dust grains of crystalline silicate, which are rarely presented in interstellar space, were found in cometary nuclei. These crystalline silicates are thought to have formed by annealing of amorphous silicate grains or direct condensation of gaseous materials near the Sun in the solar nebula, and incorporated into cometary nuclei in the cold comet-forming region after radial transportation of grains in the solar nebula. Abundances of the crystalline silicate dust grains were therefore expected to be smaller farther from the Sun. We aim to better understand the formation mechanism of minerals incorporated into comet 17P/Holmes based on its mineral abundances. To derive the mineral composition of comet 17P/Holmes, we applied a thermal emission model for cometary dust grains to mid-infrared spectra of comet 17P/Holmes taken with the Cooled Mid-Infrared Camera and Spectrograph (COMICS) mounted on the Subaru Telescope a few days later the great outburst in October 2007. The resulting mass fraction of crystalline silicate, f_ cry, and an olivine-to-pyroxene abundance ratio, f_OP, are f_cry = 0.31 +/- 0.03 and f_OP = 1.20 +0.16/-0.12, respectively. Based on a simple consideration of the mixing of dust grains originating in both the interstellar medium and solar nebula, the minerals of 17P/Holmes formed by non-equilibrium condensation. This result is consistent with theoretical and experimental predictions for vaporization and condensation of olivine in the solar nebula.