부산대학교 도서관

In the next decades, the planetary science community is preparing for the exploration of the Jupiter system with NASA's Europa Clipper mission and ESA's JUICE mission. The main objective of these missions is to characterise the subsurface structure of the Jupiter's icy moons Ganymede, Europa and Callisto. These bodies may harbor shallow saline liquid water reservoirs, and ice/ocean interfaces at depth. Part of the scientific payload of these missions includes the REASON radar sounder on Clipper (which will operate at 9 MHz and 60 MHz) and the RIME radar sounder on JUICE (9 MHz). The effect of dissolved hydrated sulfate salts on the dielectric properties of pure water is not yet well understood, although it is crucial for the interpretation of the RIME and REASON data, in particular for the search and the characterisation of subsurface saline liquid water reservoirs and deep ice/ocean interfaces. In order to provide constrains from laboratory experiments, we set up a programme of dielectric spectroscopy measurements on pure and saline liquid water in the frequency range of 40 MHz to 1 GHz using a coaxial cell adapted for the measurements of liquids. In this paper, we report the first results of these experiments. Namely, ambient temperature measurements of one deionised liquid water sample, five samples consisting of sodium chloride salt dissolved in deionised liquid water, and three samples consisting of magnesium sulfate salt dissolved in purified liquid water. We show that, in the frequency range of the measurements, the effect on the complex permittivity of the dissolved magnesium sulfate salt is smaller than that of the dissolved sodium chloride. Besides, our results suggest to take into account a decrease of the real and the imaginary parts of the complex permittivity from 9 MHz to 60 MHz in radar propagation models involving a dielectric interface with a liquid water reservoir in which hydrated magnesium sulfate salts are dissolved.