The reflectance of ice/dust associations.
Abstract
Association and segregation of volatiles and refractories are among the most important processes in the scenarios of formation and evolution of planets. In this scenario, the H_{2}O molecule plays a unique role because its abundance and unique properties. Also, the H _{2}O molecule interacts with the electromagnetic field over most of the spectrum, making it possible to identify and characterize water -mostly its solid form- on planetary surfaces using different and complementary remote-sensing techniques.Because of the complexity of the interactions between light and the particulate layer (regolith) that covers most planetary objects in the Solar System, the physical models necessary for the quantitative inversion of remote-sensing data must be thoroughly tested to assess the accuracy of the retrieved values of various properties. This is particularly critical in the optical domain where a multitude of physical and chemical parameters influence the reflectance of the surface. Laboratory experiments with macroscopic analogues that reproduce part of the complexity of natural surfaces, but are nevertheless well-characterized quantitatively, are key for the assessment of the qualities and limitations of models. Libraries of reflectance data collected with series of well-characterized samples can also be used for direct comparisons with spacecraft data when model cannot be used. Working with well-characterized icy samples to be used as references is particularly complicated as the samples tend to be prone to fast metamorphism and caution must be taken at all times to keep them pristine.The Laboratory for Outflow Studies of Sublimating icy materials (LOSSy) has been developed for this purpose at the University of Bern since 2010 [1,2]. We have built machines and developed protocols to produce various types of icy analogues in reproducible ways. This includes intimate mixtures of ice and dust, grains of ice with dust embedded into the ice or frost grown onto a dust substrate [3,4]. In addition to H _{2}O ice, we have also started experimenting with CO _{2} ice. In our laboratory, we measure the reflectance properties of these samples as a function of wavelength (spectra) and illumination and measurement geometry (Bidirectional Reflectance Distribution Function, BRDF). We have recently complemented our instrumentation with polarization-sensitive detectors to add this property to our photometric characterizations [5]. Through collaborations, we characterize our samples using other techniques over various spectral domains [6]. We have recently started distributing the spectro-photometric data through online databases [7].We will present different examples of our recent and current investigations that are relevant for comets, Mars polar regions, the permanently shadowed polar craters of Mercury or the surfaces of the icy satellites in the outer Solar System.References: [1] Pommerol, A. et al., PSS 59, 2011. [2] Pommerol, A. et al., PSS 109-110, 2015. [3] Yoldi et al., GRL 42, 2015. [4] Poch et al., Icarus 267, 2016. [5] Poch et al., EPSC, 2017. [6] Brouet et al., JGR 121, 2016. [7] All published BRDF data measured in LOSSy are available on the DACE database (https://dace.unige.ch/lossy/samplesearch/index) and the spectral data are under ingestion in the Bern icY Planetary Analogues Solid Spectroscopy (BYPASS) database (https://www.sshade.eu, use filter Database ="BYPASS").
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E3769Y