Nasa is set to crash two unmanned spacecraft into the Moon in a bid to detect the presence of water-ice.
A 2,200kg rocket stage will be first to collide, hurling debris high above the lunar surface.
A second spacecraft packed with science instruments will analyse the contents of this dusty cloud before meeting a similar fate.
The identification of water-ice in the impact plume would be a major discovery, scientists say.
Not least because a supply of water on the Moon would be a vital resource for future human exploration.