 A neutron <unk> on board the <unk> <unk> spacecraft detected enhanced concentrations of hydrogen close to the northern and southern lunar poles , including the crater <unk> . At the end of this mission in July 1999 , the spacecraft was crashed into the nearby crater Shoemaker in the hope of detecting from Earth @-@ based telescopes an impact @-@ generated plume containing water vapor . The impact event did not produce any detectable water vapor , and this may be an indication that the hydrogen is not in the form of hydrated minerals , or that the impact site did not contain any ice . Alternatively , it is possible that the crash did not excavate deeply enough into the <unk> to liberate significant quantities of water vapor . 
