Ko Ishibashi

Rotational-Temperature Measurements of Chemically Reacting CN Using Band-Tail Spectra

The vibrational state of chemically reacting CN radicals does not necessarily have a Boltzmann distribution because it may be influenced by the chemical reaction leading to the formation of the CN radicals. Here, we develop a new method to measure the rotational temperature of chemically reacting nonequilibrium cyanide radicals using the band tails of their emission spectra. Because of the very short relaxation time scales, both the translational and rotational states reach a thermal equilibrium even when the vibrational state does not have a Boltzmann distribution. The method proposed in this study has two advantages. First, it is not sensitively affected by self-absorption. Second, it does not require as high a wavelength resolution as other methods because it uses the overall shape of the tail part of the CN emission bands. Thus, our method is more suitable for high-speed temperature measurements, where a high-wavelength-resolution measurement is difficult to obtain. To investigate the validity of our method, we carried out laser-ablation experiments within an N 2 - H 2 O - CO 2 - Ar gas mixture using graphite targets and measured the rotational temperature of laser-induced CN and C 2 radicals using the proposed method. The rotational temperatures exhibit reasonable trends as functions of time and beam cross sections, strongly suggesting that our method is useful for translational-rotational-temperature estimation of chemically reacting nonequilibrium CN radicals.

Oxidation of carbon compounds by silica-derived oxygen within impact-induced vapor plumes

Impact-induced vapor plumes produce a variety of chemical species, which may play an important role in the evolution of planetary surface environments. In most previous theoretical studies on chemical reactions within impact-induced vapor plumes, only volatile components are considered. Chemical reactions between silicates and volatile components have been neglected. In particular, silica (SiO2) is important because it is the dominant component of silicates. Reactions between silica and carbon under static and carbon-rich “metallurgic” conditions (C/SiO2 ≫ 1) are known to occur to produce CO and SiC. Actual impact vapor plumes, however, cool dynamically and have carbon-poor “meteoritic” composition (C/SiO2 ≪ 1). Reactions under such conditions have not been investigated, and final products in such reaction systems are not known well. Although CO and SiO are thermodynamically stable at high temperatures under carbon-poor conditions, C and SiO2 are stable at low temperatures. Thus, CO may not be able to survive the rapidly cooling process of vapor plumes. In this study, we conduct laser pulse vaporization (LPV) experiments and thermodynamic calculations to examine whether interactions between carbon and silica occur in rapidly cooling vapor plumes with meteoritic chemical compositions. The experimental results indicate that even in rapidly cooling vapor plumes with meteoritic compounds are rather efficiently oxidized by silica-derived oxygen and that substantial amounts of both CO2 and CO are produced. The calculation results also suggest that those oxidation reactions seen in LPV experiments might occur in planetary-scale vapor plumes regardless of impact velocity as long as silicates vaporize.

Gas recovery experiments to determine the degree of shock-induced devolatilization of calcite

Shock-induced devolatilization of volatile-bearing minerals has played an important role in the formation of the atmosphere and evolution of surface environments of terrestrial planets. The dependence of the degree of devolatilization on ambient pressure has not been investigated in detail before, even though ambient pressure dramatically affects the degree of devolatilization. In this study, we conducted shock recovery experiments on calcite (CaCO3) using newly designed sample containers for released gas analysis, and assessed the dependence of the degree of devolatilization on the partial pressure of CO2. Our results clearly show that the degree of devolatilization increases as the sample container volume increases and the initial mass of calcite decreases.

Optical/mechanical design of the focal plane receiver of the Ganymede Laser Altimeter (GALA) for the Jupiter Icy Moons Explorer (JUICE) mission

The Jupiter Icy Moons Explorer (JUICE) mission of the European Space Agency to be launched in 2022 will provide an opportunity for a dedicated exploration of the Jovian system including its icy moons. The Ganymede Laser Altimeter (GALA) has been selected as one of the ten payloads of JUICE. GALA will enable unique studies of the topography and shape, tidal and rotational state, and geology of primarily Ganymede but also Europa and Callisto. The GALA project is an ongoing international collaboration led by Germany, together with Switzerland, Spain, and Japan. This paper presents the optical and mechanical design of the focal plane receiver, the Japanese part of GALA.