In the laboratory, we are preparing and analysing analogues of planetary and cometary surfaces composed of dust-ice or salt-ice mixtures to study their optical properties and dynamic evolution under simulated conditions (sublimation, outflow etc.). This laboratory work gives us the ability to predict photometric properties or to interpret observational data of planetary or cometary surfaces.
Our current laboratory setups consist of:
The preparation of analogues of planetary and cometary surfaces for our measurements requires the use of judiciously chosen and accurately characterised materials including ice, minerals, salts and organic matter. In addition to a collection of mineral and organic materials, we have developed an ice production machine called SPIPA for Setup for Production of Icy Planetary Analogues, capable of producing rapidly a thick layer of water ice particles needed for our measurements. We have developed protocols to prepare various types of mixtures (e.g. intimate or intra- mixtures) of these ice and contaminants in a controlled and reproducible way. The surface texture of the samples is characterised using our OCTOPUS facility, for Optical Coherence Tomography Of Planetary Ultra-cold Samples, capable to image the 3D structure of a 10*10 mm area at a resolution of a few μm and down to depths of few mm. This instrument probes the same layer of the sample that is responsible for the scattering of the light, measured by our PHIRE-2 and SCITEAS setups.
The PHIRE-2 (for Physikalisches Institut Radiometer Experiments) facility is designed to characterise the VIS–NIR Bidirectional Reflectance Distribution Function (BRDF) and some complementary bulk physical properties of planetary analogue samples containing water ice. The central part of the facility is a highly accurate gonio-radiometer (PHIRE-2) operating in the VIS–NIR spectral range (400–1100 nm) installed in a large laboratory freezer to permit operations at sub-zero temperatures. Its development was based on the experience gained on the gonio-radiometer PHIRE-1. The photometric measurements are complemented by a detailed simultaneous characterisation of the physical state and possible temporal evolution of the samples using a combination of macro- and micro-imaging, thermal, electrical and sample mass measurements. PHIRE-2 is designed to support the interpretation of current and future remote sensing and in-situ datasets on icy planetary objects with a special emphasis on cometary nuclei, Martian polar regions and Jovian satellites.
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The SCITEAS (Simulation Chamber for Imaging Temporal Evolution of Analogous Samples) facility is an original simulation chamber aiming at studying the temporal evolution of icy analogues under low temperature and low pressure conditions. The temperature field in the sample as well as its optical properties and surface texture are investigated in situ in the chamber, using sensors and a visible to near-infrared hyperspectral imaging system. Experiments conducted in this facility have provided laboratory support to interpret the investigations on comet Churyumov-Gerasimenko by the ESA Rosetta mission. SCITEAS can also simulate Mars surface temperature and pressure conditions, providing essential laboratory data for the interpretation of VIS-NIR remote sensing datasets of the Martian surface. Now, SCITEAS is also being used together with MEFISTO (link to MEFISTO) to measure the spectral properties of irradiated pure or salty ices.
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The POLICES facility is a spectro-gonio-polarimeter to measure the polarisation of a light reflected by an icy analogue.
Extensive mapping of polygonal fracture patterns on the surface of Mars suggests that polygonal desiccation crack patterns may be a common feature that is present in various size scales ranging from cm scale up to hundreds of meters. Formed by surface evaporation and/or migration of subsurface water, desiccation crack patterns represent key indicators of the past climatic conditions at the surface of Mars. As such, this work has important implications for our understanding of the history of liquid water on Mars. The desiccation experiments performed in our group on wet soil analogues in ambient and Mars-like atmospheric conditions aim to understand the processes involved on the cmscale (i.e., involving only surface evaporation), which may later be extrapolated accordingly to account for larger scales.
We plan to extend our laboratory capabilities to investigate in more detail dust-gas outflows and dust-ice interactions using the illumination of a solar simulator on icy surface samples, analogues of comets, Mercury, Mars and icy outer solar system moons. Currently, an updated version of SCITEAS is being built.
Gas-dynamical interactions with porous dust-ice structures are ubiquitously evoked to explain the formation and evolution of minor bodies in the Solar System. Hydrodynamical interactions between rarefied volatiles and refractory materials form the basis of our understanding of how solid bodies initially formed in the early Solar system and remain important with regard to the surfaces of present-day comets and icy moons. We are in the design phase for a new temperature-controlled flow vessel that will house rarefied gas, with optical access suitable to study both dynamics and light-scattering properties on ice-dust compounds subjected to a gas stream.
Our group actively collaborate to the Center for Space and Habitability (CSH) of the University of Bern by conducting investigations of the spectro-photometric properties of mixtures between ice, minerals and biotic or abiotic organic matter. Taking advantage of the PHIRE-2 and SCITEAS facilities described above, we aim to assess the potential of optical remote-sensing methods to detect living organisms at the surface of various planetary bodies, including exoplanets.