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Ultrasonic Propagation in Planetary and Interstellar Ices: An experimental approach

  • Mendonck, Michiel (author)
Publication Date
Apr 08, 2021
TU Delft Repository
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Comets are celestial objects that are thought to have formed at the outer edges of our solar system. The ices they contain is thought to be preserved since their formation in the molecular cloud phase, before the formation of the sun. The formation of ices in the molecular cloud occur via the ice mantle accretion rocess, by condensation of molecules onto the cold dust surfaces. Because of the very cold temperatures, the water molecules accreting onto dust are expected to form highly porous ice, as it occurs in the laboratory simulations. The icy grains encountering each other will form larger bodies, such as comets, and the porous ices plus the coagulation of icy grains leads to a fluffy cometary ice structure. This study explores the feasibility of porosity measurements by means of ultrasonicmeasurements in these ices. A new, small liquid N2 cooled vacuum chamber was used to perform the experiments with different type of ices. strophysical ices were grown on a methacrylate substrate on which an ultrasonic transducer was mounted that sent and received ultrasonic signals. Experiments with H2O (water) and CH3OH (methanol) were done by deposition from a gas phase while also H2O (water) and C2H5OH (ethanol) were frozen on top of the methacrylate from their liquid phase. These two type of experiments required an adapted version of the setup that allowed for experiments that can freeze ice from its liquid state at atmospheric pressure after which the rest of the experiment could take place in the vacuum chamber. From this experiment, the speed of sound in water ice could be determined as a function of temperature. A linear trend for a decreasing temperature in water ice was found with slope 2.5494m/(s°C) and an offset at 0°C of 3616.86m/s for a temperature range from 0°C to -100°C. Results show that propagation of ultrasonic waves in vacuum chamber-grown ice encounters too much attenuation that prevented a distinct signal to be detectable by the transducer. / Aerospace Engineering

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