Temperature programed desorption of water ice from the surface of amorphous carbon and silicate grains as related to planet-forming disks

Understanding the history and evolution of small bodies, such as dust grains and comets, in planet-forming disks is very important to reveal the architectural laws responsible for the creation of planetary systems. These small bodies in cold regions of the disks are typically considered as mixtures of dust particles with molecular ices, where ices cover the surface of a dust core or are actually physically mixed with dust. Whilst the first case, ice-on-dust, has been intensively studied in the laboratory in recent decades, the second case, ice-mixed-with-dust, present uncharted territory. This work is the first laboratory study of the temperature-programmed desorption (TPD) of water ice mixed with amorphous carbon and silicate grains. We show that the kinetics of desorption of H2O ice depends strongly on the dust/ice mass ratio, probably, due to the desorption of water molecules from a large surface of fractal clusters composed of carbon or silicate grains. In addition, it is shown that water ice molecules are differently bound to silicate grains in contrast to carbon. The results provide a link between the structure and morphology of small cosmic bodies and the kinetics of desorption of water ice included in them.Comment: Submitted to the Astrophysical Journa

Importance of laboratory experimental studies of silicate grains for exoplanet atmosphere characterization

The study of exoplanetary atmospheres extends the frontiers of astronomy, astrophysics, and astrochemistry. Moreover, studies of exoplanets as being linked to the search for extraterrestrial life and other habitable planets are of interest not only for scientists, but for a much wider public audience. There is much evidence that clouds exist and are common in the exoplanetary atmospheres at high temperatures. Their origin can be gas-phase condensation of silicate materials and other refractory materials. Clouds have a major impact on the planets’ observable properties. Models describing atmospheres of exoplanets and brown dwarfs point to the necessity of including nanometer-to micrometer-sized grains of silicates. Observational mid-IR spectra have also provided tentative evidence of silicate grain absorption. Thus, silicates seem to be the first target for future astronomical observations of cloudy atmospheres and for laboratory studies supporting these observations. However, high-temperature laboratory studies of optical and structural properties of refractory materials, including silicates, and of gas-grain and grain surface chemistry needed for the decoding of astronomical spectra and for the development of reliable atmospheric models present practically uncharted territory. The aim of our paper is to review previous studies of optical and chemical properties of silicate materials and to emphasize the importance and perspective of high-temperature measurements of laboratory analogues of atmospheric silicate grains for exoplanet atmosphere characterization. This is particularly important in the light of new advanced astronomical instruments, which, as we expect, will bring comprehensive information on exoplanetary atmospheres