Icy Moon Ice-Salt Measurements for Dielectric and Thermal Properties

The REASON ground penetrating radar (GPR) on Europa Clipper and the RIME GPR on JUICE will produce radargrams for Europa to determine the nature and depth of the ice overlying a putative ocean. The REASON radar is dual frequency, 9 MHz and 60 MHz, and the RIME frequency is 9 MHz. The surface temperature of Europa is between 50 and 100 Kelvin. At 9 MHz, the REASON GPR could map relative permittivity to about 30 km with a resolution of 150 m. These two GPRs may be able to spot pockets of water within the ice shell that could serve as a passageway for chemicals between the surface and the ocean below. The upper ice crust is expected to contain magnesium and sodium sulfates, and perhaps calcium sulfate [J. Moore, 1999].

To fill this gap in knowledge about the properties of the ice crust on Europa, we will make laboratory measurements of the relative permittivity (complex dielectric coefficient using impedance spectroscopy) and thermal properties (thermal conductivity and specific heat) of ice-salt mixtures at 9 and 60 MHz, over the temperature range 50 to 100 Kelvin, for the ice-salt mixtures given in Table X. This Table was provided by Kevin Collins (UCF). We do not plan to include any dust content in these ice-salt mixtures. These laboratory data may assist in the interpretation of future radargrams from RESSON and RIME

 

   TABLE 1, Europan ice-salt specimens for electrical and thermal property measurements.

Experiment NumberSalt SpeciesSalt Concentration (wt. %)Physical Texture1Sulfuric acid hydrate5Dispersed in particulate ice2Magnesium sulfate5Dispersed in particulate ice3Magnesium chloride5Dispersed in particulate ice4Sodium chloride5Dispersed in particulate ice5Magnesium sulfate1Dispersed in particulate ice6Magnesium sulfate10Dispersed in particulate ice7Magnesium sulfate25Dispersed in particulate ice8Magnesium sulfate + sulfuric acid hydrate5 (each)Dispersed in particulate ice9Magnesium sulfate5Solid block10Magnesium sulfate5Layered structure

 

We are planning also to make similar measurements of the electrical and thermal properties of ice on Titania (moon of Uramus), over temperature range of 60 to 90 Kelvin, and at 9 MHz. The surface of Titania is mainly water ice, with some frozen carbon dioxide and possibly salts. We will devise a table of salt-ice mixtures that is appropriate for Titania, based on available information on surface content.