Laboratory permittivity measurements of icy planetary analogs in the millimeter and submillimeter domains, in relation with JUICE mission.

Abstract:

The European Space Agency's JUpiter ICy moons Explorer (JUICE) spacecraft is planned for launch in 2022 and arrival at Jupiter in 2030. It will observe the planet Jupiter and three of its largest moons, Ganymede, Callisto and Europa. One instrument on the JUICE spacecraft is the Sub-millimeter Wave Instrument (SWI), which will measure brightness temperatures from Jupiter's stratosphere and troposphere, and from subsurfaces of Jupiter’s icy moons. In the baseline configuration SWI consists of two tunable sub-millimeter wave receivers operating from 530 to 625 GHz. As an alternative one of the receivers could cover the range of 1080 and 1275 GHz. Inversion models are strongly dependent on the knowledge of the complex relative permittivity (hereafter permittivity) of the target material to retrieve the physical properties of the subsurface (e.g. [1][2]).

We set up a laboratory experiment allowing us to perform reproducible measurements of the complex scattering parameters S₁₁ and S₂₁ in the ranges of 70 to 110 GHz, of 100 to 160 GHz, of 140 to 220 GHz, of 140 to 220 GHz and of 510 to 715 GHz. These scattering parameters can be used to retrieve the permittivity of icy analogs of the surfaces and subsurfaces of Jupiter's icy moons in order to prepare the data interpretation of SWI [3]. The measurements are performed under laboratory conditions with a quasi-optical bench (Institute of Applied Physics, University of Bern). The icy analogs that we prepare in the Laboratory for Outflow Studies of Sublimating Materials (LOSSy, Physics Institute, University of Bern), include two different porous water ice samples composed of fine-grained ice particles with a size range of 4 to 6 microns and ice particles with a size range of 50 to 100 microns [4][5]; and possibly CO₂ ice. We will present the general experimental set-up and the first results in the context to prepare the data interpretation of SWI.

[1] Ulaby, F. T., Long, D. G., 2014. Microwave radar and radiometric remote sensing. The University Michigan Press.

[2] Brouet Y. et al., 2015. Accepted in Astronomy and Astrophysics, Rosetta special issue.

[3] Zivkovic I., Murk A., 2012. Prof. Sandra Costanzo (Ed.), ISBN: 978-953-51-0848-1, InTech, DOI: 10.5772/51596

[4] Pommerol A. et al., 2011. Planetary and Space Science, 59:1601–1612.

[5] Jost B. et al., 2013. Icarus, 225:352–366.