re: I'm here, and thinking...
The said at the press conference that water could have percolated through the rock, that it didn't need to be a lake. Couldn't the impacts have melted the ice below to do this? They are looking in a crater so we know the impact happened there. We also know from THEMIS there is plenty of ice underground. Perhaps the impact heated the ice, produced some steam which forced its way to the surface, and then cooled into water causing the features seen.