1:45 PM - 2:00 PM
[PPS07-07] Development of 2D FT-MIR spectroscopy for SO2 frost at low temperatures to simulate Io surface environment
Jupiter's moon Io is the most volcanically active body in the solar system. Due to this volcanic activity, a tenuous atmosphere (about 10-3−10-4 Pa) containing sulfur dioxide (SO2) as the main component is formed, and SO2 frost is formed over a wide area on the surface. As the surface temperature changes rapidly from "daytime" (about 130 K) to "nighttime" or during Jupiter's eclipse (about 90 K), SO2 sublimates and deposits repeatedly, and a gas-solid phase circulation is established between the atmosphere and the surface.
Mid-infrared spectroscopic experiments simulating the Io surface environment have been conducted to clarify the relationship between the spectral shape and crystal structure of SO2 frost on the Io surface. Nash and Betts (1995) reported that the reflection absorption spectrum changes with the thickness of the frost. They also reported that frosts of various shapes occur, but only visual sketch observations using a binocular microscope have been made, and the mechanism of frost growth and its relationship to the spectra are unknown.
In this study, we report the development of a two-dimensional mid-infrared spectroscopy system for low temperature solid samples using an imaging Fourier transform mid-infrared spectrometer (2D FT-MIR) based on near-common-path wavefront-division phase-shift interferometry (Qi et al., 2015), which can be directly applied to spacecraft observations, and the results of imaging spectroscopy measurements of SO2 frost using this system. The 2D FT-MIR is based on a different operating principle from that of a general Michelson interferometer, in which a spatial phase difference is given by wavefront splitting and the interfering light component is amplified and detected at an imaging plane. Since it is a common-path interferometer, it is compact and can suppress the contribution of thermal background radiation. In parallel, we designed and fabricated a liquid nitrogen-cooled SO2 solid generation chamber that can simulate the surface temperature of Io (see figure). The SO2 solid is deposited by spraying SO2 gas onto an infrared-transparent cesium iodide (CsI) plate mounted on a cold head at the tip of a liquid nitrogen Dewar condenser in the chamber depressurized to about the atmospheric pressure of Io. Then, the temperature is raised and lowered in the range of 130−90 K corresponding to the Io surface temperature by an electrical resistance heater, and the transmission absorption imaging spectra of the SO2 frost and crystal are measured in-situ by 2D FT-MIR. In addition, by installing a rotation mechanism of the CsI plate, it is possible to measure spectra for various reflection angles.
Mid-infrared spectroscopic experiments simulating the Io surface environment have been conducted to clarify the relationship between the spectral shape and crystal structure of SO2 frost on the Io surface. Nash and Betts (1995) reported that the reflection absorption spectrum changes with the thickness of the frost. They also reported that frosts of various shapes occur, but only visual sketch observations using a binocular microscope have been made, and the mechanism of frost growth and its relationship to the spectra are unknown.
In this study, we report the development of a two-dimensional mid-infrared spectroscopy system for low temperature solid samples using an imaging Fourier transform mid-infrared spectrometer (2D FT-MIR) based on near-common-path wavefront-division phase-shift interferometry (Qi et al., 2015), which can be directly applied to spacecraft observations, and the results of imaging spectroscopy measurements of SO2 frost using this system. The 2D FT-MIR is based on a different operating principle from that of a general Michelson interferometer, in which a spatial phase difference is given by wavefront splitting and the interfering light component is amplified and detected at an imaging plane. Since it is a common-path interferometer, it is compact and can suppress the contribution of thermal background radiation. In parallel, we designed and fabricated a liquid nitrogen-cooled SO2 solid generation chamber that can simulate the surface temperature of Io (see figure). The SO2 solid is deposited by spraying SO2 gas onto an infrared-transparent cesium iodide (CsI) plate mounted on a cold head at the tip of a liquid nitrogen Dewar condenser in the chamber depressurized to about the atmospheric pressure of Io. Then, the temperature is raised and lowered in the range of 130−90 K corresponding to the Io surface temperature by an electrical resistance heater, and the transmission absorption imaging spectra of the SO2 frost and crystal are measured in-situ by 2D FT-MIR. In addition, by installing a rotation mechanism of the CsI plate, it is possible to measure spectra for various reflection angles.