  We report the detection of the 62 micron feature of crystalline water ice in
emission towards the bow-shaped Herbig-Haro object HH 7. Significant amounts of
far infrared continuum emission are also detected between 10 and 200 micron, so
that Herbig-Haro objects cease to be pure emission-line objects at FIR
wavelengths. The formation of crystalline water ice mantles requires grain
temperatures T > 100 K at the time of mantle formation, suggesting that we are
seeing material processed by the HH 7 shock front. The deduced ice mass is
\~2e-5 solar masses corresponding to a water column density N~ 1e18 cm-3; an
estimate of the [H2O]/[H] abundance yields values close to the interstellar
gas-phase oxygen abundance. The relatively high dust temperature and the
copious amounts of gas-phase water needed to produce the observed quantity of
crystalline water ice, suggest a scenario where both dissociative and
non-dissociative shocks co-exist. The timescale for ice mantle formation is of
the order of ~400 years, so that the importance of gas-phase water cooling as a
shock diagnostic may be greatly diminished.
