Schematic representation of thermal annealing process of ice mantles in circumstellar regions based on our experimental results for the warm-up of a pre-cometary ice mixture (H₂O:CO:CO₂:CH₃OH:NH₃ = 100:10–20:10–20:5:5). Red lines represent the temperature ranges at which the species used in our pre-cometary ice analogs desorb. Approximate positions of desorption peaks are indicated with vertical red lines. Desorption of NH₃ and CH₃OH prior to volcano desorption takes place when their abundance relative to water is above ~3% in the ice. Blue lines represent the temperature ranges at which structural changes in the ice occur. The top temperature scale corresponds to a heating rate of 1–2 K/min (used in experiments E10 and E11 with our pre-cometary ice mixtures and also suited to the “flash-heating” of dust grains during the periodic radial excursions considered in the fluctuating X-wind model for CAIs and chondrules formation). The bottom temperature scale corresponds to a first approximation to grains at a certain distance heated with a heating rate of 1 K/century, see text for details.