Study: Mars is rocked by asteroids, comets each day

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5. Lunar Impact Monitoring

... On average, 33 metric tons (73,000 lbs) of meteoroids hit Earth every day, the vast majority of which harmlessly ablates ("burns up&quot high in the atmosphere ... The moon, however, has no atmosphere, so meteoroids have nothing to stop them from striking the surface. The slowest of these rocks travels at 20 km/sec (45,000 mph); the fastest travels at over 72 km/sec (160,000 mph). At such speeds even a small meteoroid has incredible energy -- one with a mass of only 5 kg (10 lbs) can excavate a crater over 9 meters (30 ft) across ....

... Current meteoroid models indicate that the moon is struck by a meteoroid with a mass greater than 1 kg (2 lbs) over 260 times per year. This number is very uncertain, however, as observations for objects in this mass range are embarrassingly few -- a single fireball survey conducted by Canadian researchers from 1971 to 1985 ...

... U.S. Space Exploration Policy eventually calls for extended astronaut stays on the lunar surface ... Spacecraft, vehicles, habitats, and EVA suits must all be designed to withstand the stresses posed by the harsh lunar environment ...

... A second part, produced by meteor showers, is also present to varying degrees at certain times of the year. It is well known that the Earth experiences meteor showers when it encounters the debris left behind by comets; so too does the moon, though perhaps at not exactly the same time. On Earth these showers are capable of producing spectacular celestial fireworks displays, delighting the public. On the airless moon, however, these showers are swarms of high energy projectiles, producing fireworks only when they strike the surface with tremendous force. During such times, the rate of shower meteoroids can greatly exceed that of the sporadic background rate ...

http://www.nasa.gov/centers/marshall/news/lunar/program_overview.html