Optical Properties of Ices From UV to Infrared

Abstract

Remote sensing of ices at the surfaces and in the atmospheres of system solar objects are the subject of increasing studies in the UV, visible and infrared ranges. The spectra-imagers and spectrophotometers aboard space probes will further expand these studies. One critical problem for the interpretation of the astronomical absorption and emission spectra is the availability of laboratory data on the optical properties of the relevant ices. After a discussion of the different types of observations and their specific spectral ranges, we review the different types of laboratory measurements of the optical properties of ices and discuss the problem of optical constant calculation in each case. The various physical parameters (i. e. phase, crystalline quality, temperature and thermal history, isotopes) that influence the spectra of pure ices are analyzed. Similarly, we discuss the optical properties of mixtures and their dependence on the type of mixture (solid solution, specific compound or multi-phase system) as well as on various physical parameters (temper-ature, composition, phase, thermodynamical state). A brief summary of the available optical properties of ices and mixtures of planetary interest is followed by an assessement of what is still unknown (or poorly known) in the field. Finally, we discuss the use of laboratory data in reflectance and emittance models.