14:45 〜 15:00
[PPS01-05] Elastic wave velocities of laboratory analogs of Titan’s organic materials
キーワード：NASAドラゴンフライミッション、土星衛星タイタン、有機物エアロゾル、地震波探査
Titan’s surface is covered with organic materials, which would be originally formed in the atmosphere via photochemical reactions (e.g., Waite et al., 2007; Vuitton et al., 2019). The goals of NASA’s Dragonfly mission include to understand the chemical compositions of the surface materials and surface processes on Titan. The Dragonfly spacecraft will perform an active seismic survey using an onboarded instrument, DraGMet, to understand shallow subsurface structures of Titan (e.g., Lorenz et al., 2018). To this end, the elastic wave velocities of target materials (e.g., Titan’s organic aerosols) are required.
Here, we report results of measurement of elastic wave (P-wave and S-wave) velocities of laboratory analogs of Titan’s organic materials. Laboratory analogs of Titan’s organic materials (so-called Titan tholin) were produced by cold plasma irradiation onto a CH4/N2 (=1/9) gas mixture (Khare et al., 1984; Imanaka et al., 2004; Hirai et al., 2023). Then, Titan tholin was pressed to form pellet by using a hydraulic press. We applied two methods of inelastic X-ray scattering (IXS) (Baron et al., 2000) and ultrasonic pulse transmittance (Onodera et al., in prep.) to Titan tholin in order to elucidate its elastic wave velocities. The temperature conditions of the measurements are room temperature and ~90 K. The attenuation factor for each elastic wave velocity was also measured.
Our results show that Vp of Titan tholin is measured to be ~3000 m/s at 300 K in both IXS and ultrasonic pulse transmittance methods. The little dependence of Vp on wave frequency result suggests that the measured elastic constants of Titan tholin would be applicable to the active seismic survey by Dragonfly. Based on the measured Vp, Young’s modulus of Titan tholin becomes ~7 Gpa, which is consistent with the values measured with a different method previously (Yu et al., 2018). In the presentation, we will report the temperature dependence of elastic wave velocities of Titan tholin and discuss the conditions for detection of seismic echo reflected from the subsurface boundary during active seismic survey on Titan by Dragonfly.
Here, we report results of measurement of elastic wave (P-wave and S-wave) velocities of laboratory analogs of Titan’s organic materials. Laboratory analogs of Titan’s organic materials (so-called Titan tholin) were produced by cold plasma irradiation onto a CH4/N2 (=1/9) gas mixture (Khare et al., 1984; Imanaka et al., 2004; Hirai et al., 2023). Then, Titan tholin was pressed to form pellet by using a hydraulic press. We applied two methods of inelastic X-ray scattering (IXS) (Baron et al., 2000) and ultrasonic pulse transmittance (Onodera et al., in prep.) to Titan tholin in order to elucidate its elastic wave velocities. The temperature conditions of the measurements are room temperature and ~90 K. The attenuation factor for each elastic wave velocity was also measured.
Our results show that Vp of Titan tholin is measured to be ~3000 m/s at 300 K in both IXS and ultrasonic pulse transmittance methods. The little dependence of Vp on wave frequency result suggests that the measured elastic constants of Titan tholin would be applicable to the active seismic survey by Dragonfly. Based on the measured Vp, Young’s modulus of Titan tholin becomes ~7 Gpa, which is consistent with the values measured with a different method previously (Yu et al., 2018). In the presentation, we will report the temperature dependence of elastic wave velocities of Titan tholin and discuss the conditions for detection of seismic echo reflected from the subsurface boundary during active seismic survey on Titan by Dragonfly.