When Deep Impact's copper probe slammed into Comet Borrelly,
one of the unexpected results was the discovery of carbonates and
clays ejected by the impact.
Clays and carbonates shouldn't exist in the bowels of comets, since the
cometary nuclei usually spend their time in deep freeze in the outer reaches
of our solar system.
Clays and carbonates need liquid water to form in and there shouldn't be
any liquid water inside cometary nuclei....or could there be?

Ignoring the [exotic] theory about 'radiological heating' [sorry, Robert Clark]
there is a possibility that liquid water can briefly be created by meteorites
slamming into cometary nuclei.

The heat energy created by such impacts can run quite deep due to compression.
Some meteorite impacts can generate the energy of a nuclear bomb.
So sandwiched layers of ice can for a few minutes or hours melt forming pockets of trapped water, permitting muddy water to be stirred up; allowing mud to settle out of the refreezing water and harden into clays.

Ironic is the fact that the Deep Impact copper probe, crashing into the comet,
may have briefly generated enough heat to melt nearby sandwiched layers of ice
in Comet Borrelly, allowing the formation of fresh samples of clay over a short time span..