C. Santonja

New experimental sublimation energy measurements for some relevant astrophysical ices

Context. The knowledge of the sublimation energy of ices allows us to better understand the dynamics between surfaces and atmospheres of different environments of astrophysical interest where ices are present. Aims. This work is intended to provide sublimation energy values for a set of pure ices (CO, CH4 ,C O 2 ,N 2 ,a nd NH 3 )u sing an ew experimental procedure. The results were compared to some values obtained by other authors under different conditions and/or methods, to check the reliability of this new method. Methods. We used the frequency variation obtained from a quartz crystal microbalance to calculate the sublimation energy from the Polany-Wigner equation for the first time. Results. The results obtained are relevant since there are few previous values of sublimation energy reported on these molecules in these conditions of pressure and temperature, which are representative of astrophysical regions. These values are needed in models used to interpret dynamics of icy surfaces. In general, our results compare well to other ones obtained by different methods and complement those previously available.

Experimental studies of sublimation of highly volatile ices in relevance to the ices of the solar system

Studies of sublimation of complex ices prepared by deposition of gaseous CO, CH4, N2, and NH3 molecules on a cold plate have been performed. The low pressure and low temperature system was used: 10−9–10−5 mbar and the lowermost temperature 10 K. Diagnostic of composition of evaporates (at an actual temperature) was done by means of the mass spectrometer. The latter allowed following simultaneously the partial pressure of five different ions or radicals escaping from the substrate. It has been found that highly volatile molecules that were used simultaneously with the low volatile ones to form the complex ices (mixtures or clathrates) present a different sublimation pattern than the sublimation of pure high-volatile ices. In particular, the high-volatile component sublimes at two or even three different temperature regimes: At low temperature that is typical for sublimation of this component, as well as at much higher temperatures. This effect seems to be important when degassing and outbursts from cometary nuclei are considered. It can be also important for modeling of cryovolcanic processes on the icy satellites.

Density of Ices of Astrophysical Interest

Density plays an important role in the understanding of chemical and physical evolution of ices in space. It is related with abundances, energetic processing, porosity, buoyancy, etc.