4:30 PM - 4:45 PM
[PCG20-11] Hydrated silicate minerals on the surface of evolved comets
Keywords:comets, dust, phyllosilicate
Comets are thought to be the remnants of planetesimals and contain pristine materials formed in the early solar nebula. The materials of periodic comets that have orbited the Sun many times, however, are expected to evolve thermally. The comet nucleus exhibits clues to investigate significant physical and chemical evolution, including the influence of solar heating on cometary nuclei. Thus, conducting observational and theoretical studies on evolved comets is essential.
Ootsubo et al. (2021) conducted the mid-infrared imaging and spectroscopic observations of comet P/2016 BA14 (PANSTARRS)
with Cooled Mid-Infrared Camera and Spectrometer (COMICS) mounted on Subaru telescope. Its gas and dust production rates were notably low, even near the perihelion passage around 1 au from the Sun, and it was expected that the observation obtained the thermal emission from the nucleus. The normalized emissivity spectrum of Comet PANSTARRS in the mid-IR is not reproduced by the anhydrous silicate minerals, including olivine and pyroxene, which are typically found in cometary coma dust. By comparing with the thermal emissivity spectra measured for various minerals in the laboratory, the shape and position of the observed ~10-micron feature observed for Comet PANSTARRS are more similar to those of phyllosilicates rather than anhydrous silicates, which are usually not observed in the mid-infrared comet spectra. Ootsubo et al. (2021) concluded that the prominent absorption-like feature peaked at 9.50 micron in the spectrum of Comet PANSTARRS is associated with dehydroxylated phyllosilicates on the nucleus surface.
Comet PANSTARRS is the first comet that the hydrous silicate mineral is observational;y found on the nucleus surface. It is suggested that the results indicate that one possible end state of comets may be an inactive small body covered with coarse grains of phyllosilicate minerals combined with organic materials. To verify this hypothesis, mid-IR spectroscopic observations of other evolved comets are required. Comet 2P/Encke is one of the evolved comets, which has one of the shortest orbital periods of any known comet (3.3 years) within our solar system and has a cometary dust trail consisting of mm- to cm-sized dust particles. We observed comet Encke with Subaru telescope in the mid-IR on 2003 November 12 UT. Low-resolution (R~250) spectroscopic observations in the N-band and imaging observations in N- and Q-bans were carried out using COMICS. The mid-IR spectrum of comet Encke does not show distinct silicate features from small silicate grains. It looks blackbody-like, but weak negative features from the continuum can be seen. We will discuss the features and the dust properties of Comet Encke in our presentation.
Ootsubo et al. (2021) conducted the mid-infrared imaging and spectroscopic observations of comet P/2016 BA14 (PANSTARRS)
with Cooled Mid-Infrared Camera and Spectrometer (COMICS) mounted on Subaru telescope. Its gas and dust production rates were notably low, even near the perihelion passage around 1 au from the Sun, and it was expected that the observation obtained the thermal emission from the nucleus. The normalized emissivity spectrum of Comet PANSTARRS in the mid-IR is not reproduced by the anhydrous silicate minerals, including olivine and pyroxene, which are typically found in cometary coma dust. By comparing with the thermal emissivity spectra measured for various minerals in the laboratory, the shape and position of the observed ~10-micron feature observed for Comet PANSTARRS are more similar to those of phyllosilicates rather than anhydrous silicates, which are usually not observed in the mid-infrared comet spectra. Ootsubo et al. (2021) concluded that the prominent absorption-like feature peaked at 9.50 micron in the spectrum of Comet PANSTARRS is associated with dehydroxylated phyllosilicates on the nucleus surface.
Comet PANSTARRS is the first comet that the hydrous silicate mineral is observational;y found on the nucleus surface. It is suggested that the results indicate that one possible end state of comets may be an inactive small body covered with coarse grains of phyllosilicate minerals combined with organic materials. To verify this hypothesis, mid-IR spectroscopic observations of other evolved comets are required. Comet 2P/Encke is one of the evolved comets, which has one of the shortest orbital periods of any known comet (3.3 years) within our solar system and has a cometary dust trail consisting of mm- to cm-sized dust particles. We observed comet Encke with Subaru telescope in the mid-IR on 2003 November 12 UT. Low-resolution (R~250) spectroscopic observations in the N-band and imaging observations in N- and Q-bans were carried out using COMICS. The mid-IR spectrum of comet Encke does not show distinct silicate features from small silicate grains. It looks blackbody-like, but weak negative features from the continuum can be seen. We will discuss the features and the dust properties of Comet Encke in our presentation.