ANSWER: Asteroids acting as delivery vehicles
Explanation:
Researchers from Russia have discovered that water reserves on moon are the result of asteroids functioning as delivery vehicles and not falling ice comets as study using computer simulation has found. Scientists have made the discovery that a massive asteroid can deliver greater amounts of water to the lunar surface than cumulative fall of comets over a billion year period. The simulation has also shown that when short period comets fall, most of the water evaporates and less than 1 percent of it remains in impact point. Fall of asteroids containing water can generate deposits of chemically bounded water located within lunar craters.