Permanently shadowed polar craters can remain cold enough to trap waterice and other volatiles for long periods. LCROSS used an impact plume to expose and spectroscopically sample material from such acold trap, testing the interpretation of polar hydrogen signatures and the availability/history of lunar volatiles. Shadow was therefore a physical target-selection criterion, not merely an observational inconvenience.[ref]
LCROSS by NASA. Mission objective and the 9 October 2009 Cabeus impacts
