ner_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
tokens: of the material. At the surface of silicates, either hydrophilic silanol groups (Si–OH) or hydrophobic Si–O–Si groups are present. The ratio of these groups depends on the production process, the thermal treatment of the silicates, and on a possible processing of silicate surfaces. In silicates produced by laser ablation, the amount of Si–OH groups is small. However, reactions between water molecules and grains have probably increased the number of silanol groups on the surface of the grains. Consequently, the number of hydrophilic surface sites was increased. Thus, with our results, we demonstrate a principal difference between the surface properties of two classes of interstellar grains, namely, the finding of differently bound water ice molecules to silicate grains in contrast to fullerene-like carbon grains. However, this is not a general statement for carbon because carbon surfaces can be very different. For example, oxygenation of C-atoms can produce hydrophilic surface sites. 4.3. Astrophysical Implication The knowledge of the desorption properties of water ice mixed with dust is very important for the understanding of astronomical observations of water vapor in planet-forming regions and for the revealing of the architecture and evolution of planet-forming disks. The desorption of water ice triggering the release of other volatiles trapped in the ice influences the chemistry of the gas phase of disks by feeding it with molecules. In addition, the formation efficiency of larger bodies depends on the ice coverage of dust grains. Knowing the amount of ice relative to dust in a planet-forming disk and the kinetics of desorption of the ice, the structure and morphology of grains and larger bodies can be modeled. It will help to trace back the thermal history of the disk. Conversely, knowing the thermal history of a cosmic body seeded with molecular ice and the kinetics of desorption of ice, the abundance of molecules stayed in the ice and released into the gas phase can be estimated. It will improve our understanding of astrochemical processes in the gas phase and on surfaces. However, more systematic studies on the thermal desorption of molecular ices mixed with different dust analogs are needed. This work represents the first small step in this challenging direction. 5. Summary We measured the TPD of water ice, which had been premixed with amorphous carbon or silicate dust grains, and demonstrate the dependence of the kinetics of desorption of water ice on the dust/ice ratio. The desorption order increases with an increase of the dust/ice mass ratio and reaches 1, indicating the desorption of ice molecules from the large surface of dust grains. This result shows an important link between the structure and morphology of icy dust grains in planet-forming disks and the amount and the desorption properties of seeded ice. If more information on the thermal history of dust grains was known, more information about the structure and