  Asteroid (16) Psyche, that for long was the largest M-type with no detection
of hydration features in its spectrum, was recently discovered to have a weak 3
micron band and thus it eventually was added to the group of hydrated
asteroids. Its relatively high density in combination with the high radar
albedo, led to classify the asteroid as a metallic object, possibly a core of a
differentiated body, remnant of "hit-and-run" collisions. The detection of
hydration is, in principle, inconsistent with a pure metallic origin of this
body. Here we consider the scenario that the hydration on its surface is
exogenous and was delivered by hydrated impactors. We show that impacting
asteroids that belong to families whose members have the 3 m band can deliver
the hydrated material to Psyche. We developed a collisional model with which we
test all the dark carbonaceous asteroid families, which contain hydrated
members. We find that the major source of hydrated impactors is the family of
Themis, with a total implanted mass on Psyche to be of the order of 10^14 kg.
However, the hydrated fraction could be only a few per cent of the implanted
mass, as the water content in carbonaceous chondrite meteorites, the best
analogue for the Themis asteroid family, is typically a few per cent of their
mass.
