  Crystalline silicates are found in a large number of comets. These pose a
long-standing conundrum for solar system formation models as they can only be
created in the inner hot disk at temperatures higher than 800 K, and there is
no obvious mechanism to transport them out into the comets formation region.
Here we propose that these particles could have formed inside the hydrostatic
envelopes surrounding young protoplanets still embedded in the protoplanetary
disk. Using a simplified 1D model we investigate the thermal structure of these
envelopes, and find that for core masses ranging from 0.08 to 1.5 M_Earth,
located anywhere between 1 and 30 AU, the temperature and pressure at the base
of the envelopes are high enough to quickly vaporize silicate particles of
various sizes. Moreover, if the grain abundance is at least solar, these
envelopes become fully convective, allowing for dust ejection across the Bondi
radius back into the disk. Amorphous silicates are hence thermally processed
into crystalline particles in these envelopes, and then transported back to
disk through convective diffusion to be finally incorporated into the cometary
building blocks.
