Laboratory Simulation of Sublimating Planetary Surface Ices: Experiment Design and Thermal Considerations
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We have constructed a set of experimental apparatus to simulate the thermal environment at the surface of icy moons. Most of these moons, such as Europa, have little or no atmosphere, and therefore no liquid phase of water. This environment can create sublimation-driven surface morphologies, such as ice penitentes, which often exist on high-altitude terrestrial snowfields at scales of 2m or more, and which are highly relevant to potential lander spacecraft. Our experimental devices consist of several 30-cm-scale static testbeds, and a 1-m-scale diurnal testbed. The static testbeds provide an economical means to perform short-duration tests at moderate temperatures and vacuum levels (-40oC to 0oC and 0.1 Torr to atmospheric), with solar illumination up to 1300 W/m2. In this regime, the surface evolves rapidly due to high sublimation rates, and enables a wide range of experiments with varying temperature, pressure, and ice composition to examine surface growth trends. The diurnal testbed provides bulk ice samples of 70K – 200K with background pressure of 10-6 Torr, and an illumination source mounted to a cryogenic mechanical stage to simulate diurnal variation. This apparatus enables long term (~months) tests at relevant planetary surface thermal conditions.